Teach drag start behaviors to DragGestureRecognizer (#23424)

* Adds start behavior option to the drag gesture recognizer and makes it the default option when a drag gesture recognizer is created. Also fixes all the tests to work correctly with the new default behavior.

examples/flutter_gallery/lib/demo/material/drawer_demo.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../../gallery/demo.dart';
 
@@ -79,6 +80,7 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
+      drawerDragStartBehavior: DragStartBehavior.down,
       key: _scaffoldKey,
       appBar: AppBar(
         leading: IconButton(
@@ -106,6 +108,7 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
               ),
               otherAccountsPictures: <Widget>[
                 GestureDetector(
+                  dragStartBehavior: DragStartBehavior.down,
                   onTap: () {
                     _onOtherAccountsTap(context);
                   },
@@ -120,6 +123,7 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
                   ),
                 ),
                 GestureDetector(
+                  dragStartBehavior: DragStartBehavior.down,
                   onTap: () {
                     _onOtherAccountsTap(context);
                   },
@@ -149,6 +153,7 @@ class _DrawerDemoState extends State<DrawerDemo> with TickerProviderStateMixin {
               removeTop: true,
               child: Expanded(
                 child: ListView(
+                  dragStartBehavior: DragStartBehavior.down,
                   padding: const EdgeInsets.only(top: 8.0),
                   children: <Widget>[
                     Stack(

examples/flutter_gallery/lib/demo/material/text_form_field_demo.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../../gallery/demo.dart';
 
@@ -67,6 +68,7 @@ class _PasswordFieldState extends State<PasswordField> {
         labelText: widget.labelText,
         helperText: widget.helperText,
         suffixIcon: GestureDetector(
+          dragStartBehavior: DragStartBehavior.down,
           onTap: () {
             setState(() {
               _obscureText = !_obscureText;
@@ -167,6 +169,7 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
+      drawerDragStartBehavior: DragStartBehavior.down,
       key: _scaffoldKey,
       appBar: AppBar(
         title: const Text('Text fields'),
@@ -180,6 +183,7 @@ class TextFormFieldDemoState extends State<TextFormFieldDemo> {
           autovalidate: _autovalidate,
           onWillPop: _warnUserAboutInvalidData,
           child: SingleChildScrollView(
+            dragStartBehavior: DragStartBehavior.down,
             padding: const EdgeInsets.symmetric(horizontal: 16.0),
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.stretch,

examples/stocks/lib/stock_home.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart' show debugDumpRenderTree, debugDumpLayerTree, debugDumpSemanticsTree, DebugSemanticsDumpOrder;
 import 'package:flutter/scheduler.dart' show timeDilation;
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 import 'stock_data.dart';
 import 'stock_list.dart';
 import 'stock_strings.dart';
@@ -110,6 +111,7 @@ class StockHomeState extends State<StockHome> {
   Widget _buildDrawer(BuildContext context) {
     return Drawer(
       child: ListView(
+        dragStartBehavior: DragStartBehavior.down,
         children: <Widget>[
           const DrawerHeader(child: Center(child: Text('Stocks'))),
           const ListTile(
@@ -317,11 +319,13 @@ class StockHomeState extends State<StockHome> {
     return DefaultTabController(
       length: 2,
       child: Scaffold(
+        drawerDragStartBehavior: DragStartBehavior.down,
         key: _scaffoldKey,
         appBar: _isSearching ? buildSearchBar() : buildAppBar(),
         floatingActionButton: buildFloatingActionButton(),
         drawer: _buildDrawer(context),
         body: TabBarView(
+          dragStartBehavior: DragStartBehavior.down,
           children: <Widget>[
             _buildStockTab(context, StockHomeTab.market, widget.stocks.allSymbols),
             _buildStockTab(context, StockHomeTab.portfolio, portfolioSymbols),

packages/flutter/lib/src/cupertino/switch.dart

@@ -52,12 +52,16 @@ import 'thumb_painter.dart';
 ///  * <https://developer.apple.com/ios/human-interface-guidelines/controls/switches/>
 class CupertinoSwitch extends StatefulWidget {
   /// Creates an iOS-style switch.
+  ///
+  /// [dragStartBehavior] must not be null.
   const CupertinoSwitch({
     Key key,
     @required this.value,
     @required this.onChanged,
     this.activeColor,
-  }) : super(key: key);
+    this.dragStartBehavior = DragStartBehavior.start,
+  }) : assert(dragStartBehavior != null),
+       super(key: key);
 
   /// Whether this switch is on or off.
   final bool value;
@@ -92,6 +96,26 @@ class CupertinoSwitch extends StatefulWidget {
   /// [CupertinoTheme] in accordance to native iOS behavior.
   final Color activeColor;
 
+  /// {@template flutter.cupertino.switch.dragStartBehavior}
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], the drag behavior used to move the
+  /// switch from on to off will begin upon the detection of a drag gesture. If
+  /// set to [DragStartBehavior.down] it will begin when a down event is first
+  /// detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  /// {@endtemplate}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _CupertinoSwitchState createState() => _CupertinoSwitchState();
 
@@ -111,6 +135,7 @@ class _CupertinoSwitchState extends State<CupertinoSwitch> with TickerProviderSt
       activeColor: widget.activeColor ?? CupertinoColors.activeGreen,
       onChanged: widget.onChanged,
       vsync: this,
+      dragStartBehavior: widget.dragStartBehavior,
     );
   }
 }
@@ -122,12 +147,14 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
     this.activeColor,
     this.onChanged,
     this.vsync,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : super(key: key);
 
   final bool value;
   final Color activeColor;
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;
+  final DragStartBehavior dragStartBehavior;
 
   @override
   _RenderCupertinoSwitch createRenderObject(BuildContext context) {
@@ -137,6 +164,7 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       onChanged: onChanged,
       textDirection: Directionality.of(context),
       vsync: vsync,
+      dragStartBehavior: dragStartBehavior
     );
   }
 
@@ -147,7 +175,8 @@ class _CupertinoSwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..activeColor = activeColor
       ..onChanged = onChanged
       ..textDirection = Directionality.of(context)
-      ..vsync = vsync;
+      ..vsync = vsync
+      ..dragStartBehavior = dragStartBehavior;
   }
 }
 
@@ -171,6 +200,7 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     ValueChanged<bool> onChanged,
     @required TextDirection textDirection,
     @required TickerProvider vsync,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : assert(value != null),
        assert(activeColor != null),
        assert(vsync != null),
@@ -188,7 +218,8 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     _drag = HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
-      ..onEnd = _handleDragEnd;
+      ..onEnd = _handleDragEnd
+      ..dragStartBehavior = dragStartBehavior;
     _positionController = AnimationController(
       duration: _kToggleDuration,
       value: value ? 1.0 : 0.0,
@@ -276,6 +307,14 @@ class _RenderCupertinoSwitch extends RenderConstrainedBox {
     markNeedsPaint();
   }
 
+  DragStartBehavior get dragStartBehavior => _drag.dragStartBehavior;
+  set dragStartBehavior(DragStartBehavior value) {
+    assert(value != null);
+    if (_drag.dragStartBehavior == value)
+      return;
+    _drag.dragStartBehavior = value;
+  }
+
   bool get isInteractive => onChanged != null;
 
   TapGestureRecognizer _tap;

packages/flutter/lib/src/gestures/monodrag.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/foundation.dart';
+
 import 'arena.dart';
 import 'constants.dart';
 import 'drag_details.dart';
@@ -48,7 +50,36 @@ typedef GestureDragCancelCallback = void Function();
 ///  * [PanGestureRecognizer], for drags that are not locked to a single axis.
 abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   /// Initialize the object.
-  DragGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);
+  ///
+  /// [dragStartBehavior] must not be null.
+  DragGestureRecognizer({
+    Object debugOwner,
+    this.dragStartBehavior = DragStartBehavior.start,
+  }) : assert(dragStartBehavior != null),
+       super(debugOwner: debugOwner);
+
+  /// Configure the behavior of offsets sent to [onStart].
+  ///
+  /// If set to [DragStartBehavior.start], the [onStart] callback will be called at the time and
+  /// position when the gesture detector wins the arena. If [DragStartBehavior.down],
+  /// [onStart] will be called at the time and position when a down event was
+  /// first detected.
+  ///
+  /// For more information about the gesture arena:
+  /// https://flutter.io/docs/development/ui/advanced/gestures#gesture-disambiguation
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// ## Example:
+  ///
+  /// A finger presses down on the screen with offset (500.0, 500.0),
+  /// and then moves to position (510.0, 500.0) before winning the arena.
+  /// With [dragStartBehavior] set to [DragStartBehavior.down], the [onStart]
+  /// callback will be called at the time corresponding to the touch's position
+  /// at (500.0, 500.0). If it is instead set to [DragStartBehavior.start],
+  /// [onStart] will be called at the time corresponding to the touch's position
+  /// at (510.0, 500.0).
+  DragStartBehavior dragStartBehavior;
 
   /// A pointer has contacted the screen and might begin to move.
   ///
@@ -60,6 +91,11 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
   ///
   /// The position of the pointer is provided in the callback's `details`
   /// argument, which is a [DragStartDetails] object.
+  ///
+  /// Depending on the value of [dragStartBehavior], this function will be
+  /// called on the initial touch down, if set to [DragStartBehavior.down] or
+  /// when the drag gesture is first detected, if set to
+  /// [DragStartBehavior.start].
   GestureDragStartCallback onStart;
 
   /// A pointer that is in contact with the screen and moving has moved again.
@@ -163,6 +199,16 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
       _state = _DragState.accepted;
       final Offset delta = _pendingDragOffset;
       final Duration timestamp = _lastPendingEventTimestamp;
+      Offset updateDelta;
+      switch (dragStartBehavior) {
+        case DragStartBehavior.start:
+          _initialPosition = _initialPosition + delta;
+          updateDelta = Offset.zero;
+          break;
+        case DragStartBehavior.down:
+          updateDelta = _getDeltaForDetails(delta);
+          break;
+      }
       _pendingDragOffset = Offset.zero;
       _lastPendingEventTimestamp = null;
       if (onStart != null) {
@@ -171,13 +217,12 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
           globalPosition: _initialPosition,
         )));
       }
-      if (delta != Offset.zero && onUpdate != null) {
+      if (updateDelta != Offset.zero && onUpdate != null) {
-        final Offset deltaForDetails = _getDeltaForDetails(delta);
         invokeCallback<void>('onUpdate', () => onUpdate(DragUpdateDetails(
           sourceTimeStamp: timestamp,
-          delta: deltaForDetails,
+          delta: updateDelta,
-          primaryDelta: _getPrimaryValueFromOffset(delta),
+          primaryDelta: _getPrimaryValueFromOffset(updateDelta),
-          globalPosition: _initialPosition + deltaForDetails,
+          globalPosition: _initialPosition + updateDelta, // Only adds delta for down behaviour
         )));
       }
     }
@@ -232,6 +277,11 @@ abstract class DragGestureRecognizer extends OneSequenceGestureRecognizer {
     _velocityTrackers.clear();
     super.dispose();
   }
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(EnumProperty<DragStartBehavior>('Start Behavior', dragStartBehavior));
+  }
 }
 
 /// Recognizes movement in the vertical direction.
@@ -280,7 +330,8 @@ class VerticalDragGestureRecognizer extends DragGestureRecognizer {
 ///    track each touch point independently.
 class HorizontalDragGestureRecognizer extends DragGestureRecognizer {
   /// Create a gesture recognizer for interactions in the horizontal axis.
-  HorizontalDragGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);
+  HorizontalDragGestureRecognizer({ Object debugOwner }) :
+        super(debugOwner: debugOwner);
 
   @override
   bool _isFlingGesture(VelocityEstimate estimate) {

packages/flutter/lib/src/gestures/recognizer.dart

@@ -24,6 +24,24 @@ export 'pointer_router.dart' show PointerRouter;
 /// anonymous functions that return objects of particular types.
 typedef RecognizerCallback<T> = T Function();
 
+/// Configuration of offset passed to [DragStartDetails].
+///
+/// The settings determines when a drag formally starts when the user
+/// initiates a drag.
+///
+/// See also:
+///
+///   * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+enum DragStartBehavior {
+  /// Set the initial offset, at the position where the first down even was
+  /// detected.
+  down,
+
+  /// Set the initial position at the position where the drag start event was
+  /// detected.
+  start,
+}
+
 /// The base class that all gesture recognizers inherit from.
 ///
 /// Provides a basic API that can be used by classes that work with

packages/flutter/lib/src/material/date_picker.dart

@@ -8,6 +8,7 @@ import 'dart:math' as math;
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'button_bar.dart';
 import 'button_theme.dart';
@@ -250,10 +251,12 @@ class DayPicker extends StatelessWidget {
     @required this.lastDate,
     @required this.displayedMonth,
     this.selectableDayPredicate,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(selectedDate != null),
        assert(currentDate != null),
        assert(onChanged != null),
        assert(displayedMonth != null),
+       assert(dragStartBehavior != null),
        assert(!firstDate.isAfter(lastDate)),
        assert(selectedDate.isAfter(firstDate) || selectedDate.isAtSameMomentAs(firstDate)),
        super(key: key);
@@ -281,6 +284,13 @@ class DayPicker extends StatelessWidget {
   /// Optional user supplied predicate function to customize selectable days.
   final SelectableDayPredicate selectableDayPredicate;
 
+  /// The initial drag behavior of the date picker wheel.
+  ///
+  /// If set to [DragStartBehavior.start], picker drag behavior will begin upon the
+  /// drag gesture winning the arena. If set to [DragStartBehavior.down] it will
+  /// begin when a down event is first detected.
+  final DragStartBehavior dragStartBehavior;
+
   /// Builds widgets showing abbreviated days of week. The first widget in the
   /// returned list corresponds to the first day of week for the current locale.
   ///
@@ -442,6 +452,7 @@ class DayPicker extends StatelessWidget {
               onChanged(dayToBuild);
             },
             child: dayWidget,
+            dragStartBehavior: dragStartBehavior,
           );
         }
 
@@ -502,6 +513,7 @@ class MonthPicker extends StatefulWidget {
     @required this.firstDate,
     @required this.lastDate,
     this.selectableDayPredicate,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(selectedDate != null),
        assert(onChanged != null),
        assert(!firstDate.isAfter(lastDate)),
@@ -525,6 +537,9 @@ class MonthPicker extends StatefulWidget {
   /// Optional user supplied predicate function to customize selectable days.
   final SelectableDayPredicate selectableDayPredicate;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _MonthPickerState createState() => _MonthPickerState();
 }
@@ -609,6 +624,7 @@ class _MonthPickerState extends State<MonthPicker> with SingleTickerProviderStat
       lastDate: widget.lastDate,
       displayedMonth: month,
       selectableDayPredicate: widget.selectableDayPredicate,
+      dragStartBehavior: widget.dragStartBehavior,
     );
   }
 
@@ -669,6 +685,7 @@ class _MonthPickerState extends State<MonthPicker> with SingleTickerProviderStat
                   return false;
                 },
                 child: PageView.builder(
+                  dragStartBehavior: widget.dragStartBehavior,
                   key: ValueKey<DateTime>(widget.selectedDate),
                   controller: _dayPickerController,
                   scrollDirection: Axis.horizontal,
@@ -759,6 +776,7 @@ class YearPicker extends StatefulWidget {
     @required this.onChanged,
     @required this.firstDate,
     @required this.lastDate,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(selectedDate != null),
        assert(onChanged != null),
        assert(!firstDate.isAfter(lastDate)),
@@ -778,6 +796,9 @@ class YearPicker extends StatefulWidget {
   /// The latest date the user is permitted to pick.
   final DateTime lastDate;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _YearPickerState createState() => _YearPickerState();
 }
@@ -801,6 +822,7 @@ class _YearPickerState extends State<YearPicker> {
     final ThemeData themeData = Theme.of(context);
     final TextStyle style = themeData.textTheme.body1;
     return ListView.builder(
+      dragStartBehavior: widget.dragStartBehavior,
       controller: scrollController,
       itemExtent: _itemExtent,
       itemCount: widget.lastDate.year - widget.firstDate.year + 1,

packages/flutter/lib/src/material/drawer.dart

@@ -6,6 +6,7 @@ import 'dart:math';
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'colors.dart';
 import 'debug.dart';
@@ -179,7 +180,9 @@ class DrawerController extends StatefulWidget {
     @required this.child,
     @required this.alignment,
     this.drawerCallback,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(child != null),
+       assert(dragStartBehavior != null),
        assert(alignment != null),
        super(key: key);
 
@@ -197,6 +200,26 @@ class DrawerController extends StatefulWidget {
   /// Optional callback that is called when a [Drawer] is opened or closed.
   final DrawerCallback drawerCallback;
 
+  /// {@template flutter.material.drawer.dragStartBehavior}
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], the drag behavior used for opening
+  /// and closing a drawer will begin upon the detection of a drag gesture. If
+  /// set to [DragStartBehavior.down] it will begin when a down event is first
+  /// detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  /// {@endtemplate}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   DrawerControllerState createState() => DrawerControllerState();
 }
@@ -399,6 +422,7 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
           onHorizontalDragEnd: _settle,
           behavior: HitTestBehavior.translucent,
           excludeFromSemantics: true,
+          dragStartBehavior: widget.dragStartBehavior,
           child: Container(width: dragAreaWidth),
         ),
       );
@@ -410,6 +434,7 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
         onHorizontalDragEnd: _settle,
         onHorizontalDragCancel: _handleDragCancel,
         excludeFromSemantics: true,
+        dragStartBehavior: widget.dragStartBehavior,
         child: RepaintBoundary(
           child: Stack(
             children: <Widget>[

packages/flutter/lib/src/material/paginated_data_table.dart

@@ -6,6 +6,7 @@ import 'dart:math' as math;
 
 import 'package:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'button_bar.dart';
 import 'button_theme.dart';
@@ -74,9 +75,11 @@ class PaginatedDataTable extends StatefulWidget {
     this.rowsPerPage = defaultRowsPerPage,
     this.availableRowsPerPage = const <int>[defaultRowsPerPage, defaultRowsPerPage * 2, defaultRowsPerPage * 5, defaultRowsPerPage * 10],
     this.onRowsPerPageChanged,
+    this.dragStartBehavior = DragStartBehavior.start,
     @required this.source
   }) : assert(header != null),
        assert(columns != null),
+       assert(dragStartBehavior != null),
        assert(columns.isNotEmpty),
        assert(sortColumnIndex == null || (sortColumnIndex >= 0 && sortColumnIndex < columns.length)),
        assert(sortAscending != null),
@@ -170,6 +173,9 @@ class PaginatedDataTable extends StatefulWidget {
   /// [PaginatedDataTable] constructor is called.
   final DataTableSource source;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   PaginatedDataTableState createState() => PaginatedDataTableState();
 }
@@ -417,6 +423,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
           ),
           SingleChildScrollView(
             scrollDirection: Axis.horizontal,
+            dragStartBehavior: widget.dragStartBehavior,
             child: DataTable(
               key: _tableKey,
               columns: widget.columns,
@@ -435,6 +442,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
               child: Container(
                 height: 56.0,
                 child: SingleChildScrollView(
+                  dragStartBehavior: widget.dragStartBehavior,
                   scrollDirection: Axis.horizontal,
                   reverse: true,
                   child: Row(

packages/flutter/lib/src/material/scaffold.dart

@@ -10,6 +10,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'app_bar.dart';
 import 'bottom_sheet.dart';
@@ -732,7 +733,10 @@ class Scaffold extends StatefulWidget {
     this.backgroundColor,
     this.resizeToAvoidBottomPadding = true,
     this.primary = true,
-  }) : assert(primary != null), super(key: key);
+    this.drawerDragStartBehavior = DragStartBehavior.start,
+  }) : assert(primary != null),
+       assert(drawerDragStartBehavior != null),
+       super(key: key);
 
   /// An app bar to display at the top of the scaffold.
   final PreferredSizeWidget appBar;
@@ -865,6 +869,9 @@ class Scaffold extends StatefulWidget {
   /// [AppBar.primary], is true.
   final bool primary;
 
+  /// {@macro flutter.material.drawer.dragStartBehavior}
+  final DragStartBehavior drawerDragStartBehavior;
+
   /// The state from the closest instance of this class that encloses the given context.
   ///
   /// Typical usage is as follows:
@@ -1500,6 +1507,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
           alignment: DrawerAlignment.end,
           child: widget.endDrawer,
           drawerCallback: _endDrawerOpenedCallback,
+          dragStartBehavior: widget.drawerDragStartBehavior,
         ),
         _ScaffoldSlot.endDrawer,
         // remove the side padding from the side we're not touching
@@ -1521,6 +1529,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
           alignment: DrawerAlignment.start,
           child: widget.drawer,
           drawerCallback: _drawerOpenedCallback,
+          dragStartBehavior: widget.drawerDragStartBehavior,
         ),
         _ScaffoldSlot.drawer,
         // remove the side padding from the side we're not touching

packages/flutter/lib/src/material/switch.dart

@@ -73,7 +73,9 @@ class Switch extends StatefulWidget {
     this.activeThumbImage,
     this.inactiveThumbImage,
     this.materialTapTargetSize,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : _switchType = _SwitchType.material,
+       assert(dragStartBehavior != null),
        super(key: key);
 
   /// Creates a [CupertinoSwitch] if the target platform is iOS, creates a
@@ -95,6 +97,7 @@ class Switch extends StatefulWidget {
     this.activeThumbImage,
     this.inactiveThumbImage,
     this.materialTapTargetSize,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : _switchType = _SwitchType.adaptive,
        super(key: key);
 
@@ -174,6 +177,9 @@ class Switch extends StatefulWidget {
 
   final _SwitchType _switchType;
 
+  /// {@macro flutter.cupertino.switch.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _SwitchState createState() => _SwitchState();
 
@@ -219,6 +225,7 @@ class _SwitchState extends State<Switch> with TickerProviderStateMixin {
     }
 
     return _SwitchRenderObjectWidget(
+      dragStartBehavior: widget.dragStartBehavior,
       value: widget.value,
       activeColor: activeThumbColor,
       inactiveColor: inactiveThumbColor,
@@ -240,6 +247,7 @@ class _SwitchState extends State<Switch> with TickerProviderStateMixin {
       height: size.height,
       alignment: Alignment.center,
       child: CupertinoSwitch(
+        dragStartBehavior: widget.dragStartBehavior,
         value: widget.value,
         onChanged: widget.onChanged,
         activeColor: widget.activeColor,
@@ -284,6 +292,7 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
     this.onChanged,
     this.vsync,
     this.additionalConstraints,
+    this.dragStartBehavior,
   }) : super(key: key);
 
   final bool value;
@@ -297,10 +306,12 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
   final ValueChanged<bool> onChanged;
   final TickerProvider vsync;
   final BoxConstraints additionalConstraints;
+  final DragStartBehavior dragStartBehavior;
 
   @override
   _RenderSwitch createRenderObject(BuildContext context) {
     return _RenderSwitch(
+      dragStartBehavior: dragStartBehavior,
       value: value,
       activeColor: activeColor,
       inactiveColor: inactiveColor,
@@ -330,6 +341,7 @@ class _SwitchRenderObjectWidget extends LeafRenderObjectWidget {
       ..onChanged = onChanged
       ..textDirection = Directionality.of(context)
       ..additionalConstraints = additionalConstraints
+      ..dragStartBehavior = dragStartBehavior
       ..vsync = vsync;
   }
 }
@@ -348,6 +360,7 @@ class _RenderSwitch extends RenderToggleable {
     @required TextDirection textDirection,
     ValueChanged<bool> onChanged,
     @required TickerProvider vsync,
+    DragStartBehavior dragStartBehavior,
   }) : assert(textDirection != null),
        _activeThumbImage = activeThumbImage,
        _inactiveThumbImage = inactiveThumbImage,
@@ -367,7 +380,8 @@ class _RenderSwitch extends RenderToggleable {
     _drag = HorizontalDragGestureRecognizer()
       ..onStart = _handleDragStart
       ..onUpdate = _handleDragUpdate
-      ..onEnd = _handleDragEnd;
+      ..onEnd = _handleDragEnd
+      ..dragStartBehavior = dragStartBehavior;
   }
 
   ImageProvider get activeThumbImage => _activeThumbImage;
@@ -428,6 +442,14 @@ class _RenderSwitch extends RenderToggleable {
     markNeedsPaint();
   }
 
+  DragStartBehavior get dragStartBehavior => _drag.dragStartBehavior;
+  set dragStartBehavior(DragStartBehavior value) {
+    assert(value != null);
+    if(_drag.dragStartBehavior == value)
+      return;
+    _drag.dragStartBehavior = value;
+  }
+
   @override
   void detach() {
     _cachedThumbPainter?.dispose();

packages/flutter/lib/src/material/tabs.dart

@@ -7,6 +7,7 @@ import 'dart:ui' show lerpDouble;
 
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'app_bar.dart';
 import 'colors.dart';
@@ -549,9 +550,11 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
     this.labelPadding,
     this.unselectedLabelColor,
     this.unselectedLabelStyle,
+    this.dragStartBehavior = DragStartBehavior.start,
     this.onTap,
   }) : assert(tabs != null),
        assert(isScrollable != null),
+       assert(dragStartBehavior != null),
        assert(indicator != null || (indicatorWeight != null && indicatorWeight > 0.0)),
        assert(indicator != null || (indicatorPadding != null)),
        super(key: key);
@@ -662,6 +665,9 @@ class TabBar extends StatefulWidget implements PreferredSizeWidget {
   /// is null then the text style of the theme's body2 definition is used.
   final TextStyle unselectedLabelStyle;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   /// An optional callback that's called when the [TabBar] is tapped.
   ///
   /// The callback is applied to the index of the tab where the tap occurred.
@@ -1011,6 +1017,7 @@ class _TabBarState extends State<TabBar> {
     if (widget.isScrollable) {
       _scrollController ??= _TabBarScrollController(this);
       tabBar = SingleChildScrollView(
+        dragStartBehavior: widget.dragStartBehavior,
         scrollDirection: Axis.horizontal,
         controller: _scrollController,
         child: tabBar,
@@ -1035,7 +1042,10 @@ class TabBarView extends StatefulWidget {
     @required this.children,
     this.controller,
     this.physics,
-  }) : assert(children != null), super(key: key);
+    this.dragStartBehavior = DragStartBehavior.start,
+  }) : assert(children != null),
+       assert(dragStartBehavior != null),
+       super(key: key);
 
   /// This widget's selection and animation state.
   ///
@@ -1057,6 +1067,9 @@ class TabBarView extends StatefulWidget {
   /// Defaults to matching platform conventions.
   final ScrollPhysics physics;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _TabBarViewState createState() => _TabBarViewState();
 }
@@ -1201,6 +1214,7 @@ class _TabBarViewState extends State<TabBarView> {
     return NotificationListener<ScrollNotification>(
       onNotification: _handleScrollNotification,
       child: PageView(
+        dragStartBehavior: widget.dragStartBehavior,
         controller: _pageController,
         physics: widget.physics == null ? _kTabBarViewPhysics : _kTabBarViewPhysics.applyTo(widget.physics),
         children: _children,

packages/flutter/lib/src/material/text_field.dart

@@ -8,6 +8,7 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart';
 
 import 'debug.dart';
 import 'feedback.dart';
@@ -127,6 +128,7 @@ class TextField extends StatefulWidget {
     this.cursorColor,
     this.keyboardAppearance,
     this.scrollPadding = const EdgeInsets.all(20.0),
+    this.dragStartBehavior = DragStartBehavior.start,
     this.enableInteractiveSelection,
     this.onTap,
   }) : assert(textAlign != null),
@@ -135,6 +137,7 @@ class TextField extends StatefulWidget {
        assert(autocorrect != null),
        assert(maxLengthEnforced != null),
        assert(scrollPadding != null),
+       assert(dragStartBehavior != null),
        assert(maxLines == null || maxLines > 0),
        assert(maxLength == null || maxLength == TextField.noMaxLength || maxLength > 0),
        keyboardType = keyboardType ?? (maxLines == 1 ? TextInputType.text : TextInputType.multiline),
@@ -346,6 +349,9 @@ class TextField extends StatefulWidget {
   /// {@macro flutter.widgets.editableText.enableInteractiveSelection}
   final bool enableInteractiveSelection;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   /// {@macro flutter.rendering.editable.selectionEnabled}
   bool get selectionEnabled {
     return enableInteractiveSelection ?? !obscureText;
@@ -669,6 +675,7 @@ class _TextFieldState extends State<TextField> with AutomaticKeepAliveClientMixi
         scrollPadding: widget.scrollPadding,
         keyboardAppearance: keyboardAppearance,
         enableInteractiveSelection: widget.enableInteractiveSelection,
+        dragStartBehavior: widget.dragStartBehavior,
       ),
     );
 

packages/flutter/lib/src/widgets/dismissible.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/gestures.dart';
+
 import 'automatic_keep_alive.dart';
 import 'basic.dart';
 import 'debug.dart';
@@ -82,8 +84,10 @@ class Dismissible extends StatefulWidget {
     this.dismissThresholds = const <DismissDirection, double>{},
     this.movementDuration = const Duration(milliseconds: 200),
     this.crossAxisEndOffset = 0.0,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(key != null),
        assert(secondaryBackground != null ? background != null : true),
+       assert(dragStartBehavior != null),
        super(key: key);
 
   /// The widget below this widget in the tree.
@@ -142,6 +146,23 @@ class Dismissible extends StatefulWidget {
   /// it is positive or negative.
   final double crossAxisEndOffset;
 
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], the drag gesture used to dismiss a
+  /// dismissible will begin upon the detection of a drag gesture. If set to
+  /// [DragStartBehavior.down] it will begin when a down event is first detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _DismissibleState createState() => _DismissibleState();
 }
@@ -327,8 +348,8 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
       Tween<Offset>(
         begin: Offset.zero,
         end: _directionIsXAxis
-               ? Offset(end, widget.crossAxisEndOffset)
+            ? Offset(end, widget.crossAxisEndOffset)
-               : Offset(widget.crossAxisEndOffset, end),
+            : Offset(widget.crossAxisEndOffset, end),
       ),
     );
   }
@@ -514,7 +535,6 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
       children.add(content);
       content = Stack(children: children);
     }
-
     // We are not resizing but we may be being dragging in widget.direction.
     return GestureDetector(
       onHorizontalDragStart: _directionIsXAxis ? _handleDragStart : null,
@@ -524,7 +544,8 @@ class _DismissibleState extends State<Dismissible> with TickerProviderStateMixin
       onVerticalDragUpdate: _directionIsXAxis ? null : _handleDragUpdate,
       onVerticalDragEnd: _directionIsXAxis ? null : _handleDragEnd,
       behavior: HitTestBehavior.opaque,
-      child: content
+      child: content,
+      dragStartBehavior: widget.dragStartBehavior,
     );
   }
 }

packages/flutter/lib/src/widgets/editable_text.dart

@@ -8,6 +8,7 @@ import 'dart:ui' as ui;
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'automatic_keep_alive.dart';
 import 'basic.dart';
@@ -184,7 +185,8 @@ class EditableText extends StatefulWidget {
   /// default to [TextInputType.multiline].
   ///
   /// The [controller], [focusNode], [style], [cursorColor], [backgroundCursorColor],
-  /// [textAlign], and [rendererIgnoresPointer] arguments must not be null.
+  /// [textAlign], [dragStartBehavior] and [rendererIgnoresPointer] arguments
+  /// must not be null.
   EditableText({
     Key key,
     @required this.controller,
@@ -215,6 +217,7 @@ class EditableText extends StatefulWidget {
     this.cursorRadius,
     this.scrollPadding = const EdgeInsets.all(20.0),
     this.keyboardAppearance = Brightness.light,
+    this.dragStartBehavior = DragStartBehavior.start,
     this.enableInteractiveSelection,
   }) : assert(controller != null),
        assert(focusNode != null),
@@ -228,6 +231,7 @@ class EditableText extends StatefulWidget {
        assert(autofocus != null),
        assert(rendererIgnoresPointer != null),
        assert(scrollPadding != null),
+       assert(dragStartBehavior != null),
        keyboardType = keyboardType ?? (maxLines == 1 ? TextInputType.text : TextInputType.multiline),
        inputFormatters = maxLines == 1
            ? (
@@ -284,6 +288,10 @@ class EditableText extends StatefulWidget {
   /// its left.
   ///
   /// Defaults to the ambient [Directionality], if any.
+  ///
+  /// See also:
+  ///
+  ///   * {@macro flutter.gestures.monodrag.dragStartExample}
   /// {@endtemplate}
   final TextDirection textDirection;
 
@@ -494,6 +502,9 @@ class EditableText extends StatefulWidget {
   /// Defaults to false, resulting in a typical blinking cursor.
   static bool debugDeterministicCursor = false;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   /// {@macro flutter.rendering.editable.selectionEnabled}
   bool get selectionEnabled {
     return enableInteractiveSelection ?? !obscureText;
@@ -840,6 +851,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
         renderObject: renderObject,
         selectionControls: widget.selectionControls,
         selectionDelegate: this,
+        dragStartBehavior: widget.dragStartBehavior,
       );
       final bool longPress = cause == SelectionChangedCause.longPress;
       if (cause != SelectionChangedCause.keyboard && (_value.text.isNotEmpty || longPress))
@@ -1061,6 +1073,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       axisDirection: _isMultiline ? AxisDirection.down : AxisDirection.right,
       controller: _scrollController,
       physics: const ClampingScrollPhysics(),
+      dragStartBehavior: widget.dragStartBehavior,
       viewportBuilder: (BuildContext context, ViewportOffset offset) {
         return CompositedTransformTarget(
           link: _layerLink,

packages/flutter/lib/src/widgets/gesture_detector.dart

@@ -184,8 +184,10 @@ class GestureDetector extends StatelessWidget {
     this.onScaleUpdate,
     this.onScaleEnd,
     this.behavior,
-    this.excludeFromSemantics = false
+    this.excludeFromSemantics = false,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(excludeFromSemantics != null),
+       assert(dragStartBehavior != null),
        assert(() {
          final bool haveVerticalDrag = onVerticalDragStart != null || onVerticalDragUpdate != null || onVerticalDragEnd != null;
          final bool haveHorizontalDrag = onHorizontalDragStart != null || onHorizontalDragUpdate != null || onHorizontalDragEnd != null;
@@ -370,6 +372,23 @@ class GestureDetector extends StatelessWidget {
   /// duplication of information.
   final bool excludeFromSemantics;
 
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], gesture drag behavior will
+  /// begin upon the detection of a drag gesture. If set to
+  /// [DragStartBehavior.down] it will begin when a down event is first detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  final DragStartBehavior dragStartBehavior;
+
   @override
   Widget build(BuildContext context) {
     final Map<Type, GestureRecognizerFactory> gestures = <Type, GestureRecognizerFactory>{};
@@ -421,7 +440,8 @@ class GestureDetector extends StatelessWidget {
             ..onStart = onVerticalDragStart
             ..onUpdate = onVerticalDragUpdate
             ..onEnd = onVerticalDragEnd
-            ..onCancel = onVerticalDragCancel;
+            ..onCancel = onVerticalDragCancel
+            ..dragStartBehavior = dragStartBehavior;
         },
       );
     }
@@ -439,7 +459,8 @@ class GestureDetector extends StatelessWidget {
             ..onStart = onHorizontalDragStart
             ..onUpdate = onHorizontalDragUpdate
             ..onEnd = onHorizontalDragEnd
-            ..onCancel = onHorizontalDragCancel;
+            ..onCancel = onHorizontalDragCancel
+            ..dragStartBehavior = dragStartBehavior;
         },
       );
     }
@@ -457,7 +478,8 @@ class GestureDetector extends StatelessWidget {
             ..onStart = onPanStart
             ..onUpdate = onPanUpdate
             ..onEnd = onPanEnd
-            ..onCancel = onPanCancel;
+            ..onCancel = onPanCancel
+            ..dragStartBehavior = dragStartBehavior;
         },
       );
     }
@@ -497,6 +519,11 @@ class GestureDetector extends StatelessWidget {
       child: child,
     );
   }
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+    super.debugFillProperties(properties);
+    properties.add(EnumProperty<DragStartBehavior>('startBehavior', dragStartBehavior));
+  }
 }
 
 /// A widget that detects gestures described by the given gesture
@@ -550,7 +577,7 @@ class RawGestureDetector extends StatefulWidget {
     this.child,
     this.gestures = const <Type, GestureRecognizerFactory>{},
     this.behavior,
-    this.excludeFromSemantics = false
+    this.excludeFromSemantics = false,
   }) : assert(gestures != null),
        assert(excludeFromSemantics != null),
        super(key: key);

packages/flutter/lib/src/widgets/nested_scroll_view.dart

@@ -10,6 +10,7 @@ import 'package:flutter/painting.dart';
 import 'package:flutter/physics.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'basic.dart';
 import 'framework.dart';
@@ -51,7 +52,7 @@ typedef NestedScrollViewHeaderSliversBuilder = List<Widget> Function(BuildContex
 /// in the opposite direction (e.g. allowing the user to swipe horizontally
 /// between the pages represented by the tabs, while the list scrolls
 /// vertically), then any list inside that [TabBarView] would not interact with
-/// the outer [ScrollView]. For example, flinging the inner list to scroll to
+/// the outer [ScrollView]. For example, flinginsg the inner list to scroll to
 /// the top would not cause a collapsed [SliverAppBar] in the outer [ScrollView]
 /// to expand.
 ///
@@ -188,6 +189,7 @@ class NestedScrollView extends StatefulWidget {
     this.physics,
     @required this.headerSliverBuilder,
     @required this.body,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(scrollDirection != null),
        assert(reverse != null),
        assert(headerSliverBuilder != null),
@@ -252,6 +254,9 @@ class NestedScrollView extends StatefulWidget {
   /// the [PrimaryScrollController] provided by the [NestedScrollView].
   final Widget body;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   /// Returns the [SliverOverlapAbsorberHandle] of the nearest ancestor
   /// [NestedScrollView].
   ///
@@ -338,6 +343,7 @@ class _NestedScrollViewState extends State<NestedScrollView> {
         builder: (BuildContext context) {
           _lastHasScrolledBody = _coordinator.hasScrolledBody;
           return _NestedScrollViewCustomScrollView(
+            dragStartBehavior: widget.dragStartBehavior,
             scrollDirection: widget.scrollDirection,
             reverse: widget.reverse,
             physics: widget.physics != null
@@ -365,12 +371,14 @@ class _NestedScrollViewCustomScrollView extends CustomScrollView {
     @required ScrollController controller,
     @required List<Widget> slivers,
     @required this.handle,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : super(
          scrollDirection: scrollDirection,
          reverse: reverse,
          physics: physics,
          controller: controller,
          slivers: slivers,
+         dragStartBehavior: dragStartBehavior,
        );
 
   final SliverOverlapAbsorberHandle handle;

packages/flutter/lib/src/widgets/page_view.dart

@@ -7,6 +7,7 @@ import 'dart:math' as math;
 
 import 'package:flutter/physics.dart';
 import 'package:flutter/rendering.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'basic.dart';
 import 'debug.dart';
@@ -423,6 +424,7 @@ class PageView extends StatefulWidget {
     this.pageSnapping = true,
     this.onPageChanged,
     List<Widget> children = const <Widget>[],
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : controller = controller ?? _defaultPageController,
        childrenDelegate = SliverChildListDelegate(children),
        super(key: key);
@@ -449,6 +451,7 @@ class PageView extends StatefulWidget {
     this.onPageChanged,
     @required IndexedWidgetBuilder itemBuilder,
     int itemCount,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : controller = controller ?? _defaultPageController,
        childrenDelegate = SliverChildBuilderDelegate(itemBuilder, childCount: itemCount),
        super(key: key);
@@ -464,6 +467,7 @@ class PageView extends StatefulWidget {
     this.pageSnapping = true,
     this.onPageChanged,
     @required this.childrenDelegate,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(childrenDelegate != null),
        controller = controller ?? _defaultPageController,
        super(key: key);
@@ -516,6 +520,9 @@ class PageView extends StatefulWidget {
   /// respectively.
   final SliverChildDelegate childrenDelegate;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   @override
   _PageViewState createState() => _PageViewState();
 }
@@ -562,6 +569,7 @@ class _PageViewState extends State<PageView> {
         return false;
       },
       child: Scrollable(
+        dragStartBehavior: widget.dragStartBehavior,
         axisDirection: axisDirection,
         controller: widget.controller,
         physics: physics,

packages/flutter/lib/src/widgets/scroll_view.dart

@@ -5,6 +5,7 @@
 import 'dart:math' as math;
 
 import 'package:flutter/rendering.dart';
+import 'package:flutter/gestures.dart';
 
 import 'basic.dart';
 import 'framework.dart';
@@ -60,8 +61,10 @@ abstract class ScrollView extends StatelessWidget {
     this.shrinkWrap = false,
     this.cacheExtent,
     this.semanticChildCount,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(reverse != null),
        assert(shrinkWrap != null),
+       assert(dragStartBehavior != null),
        assert(!(controller != null && primary == true),
            'Primary ScrollViews obtain their ScrollController via inheritance from a PrimaryScrollController widget. '
            'You cannot both set primary to true and pass an explicit controller.'
@@ -187,6 +190,9 @@ abstract class ScrollView extends StatelessWidget {
   ///  * [SemanticsConfiguration.scrollChildCount], the corresponding semantics property.
   final int semanticChildCount;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   /// Returns the [AxisDirection] in which the scroll view scrolls.
   ///
   /// Combines the [scrollDirection] with the [reverse] boolean to obtain the
@@ -246,6 +252,7 @@ abstract class ScrollView extends StatelessWidget {
       ? PrimaryScrollController.of(context)
       : controller;
     final Scrollable scrollable = Scrollable(
+      dragStartBehavior: dragStartBehavior,
       axisDirection: axisDirection,
       controller: scrollController,
       physics: physics,
@@ -397,6 +404,7 @@ class CustomScrollView extends ScrollView {
     double cacheExtent,
     this.slivers = const <Widget>[],
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : super(
     key: key,
     scrollDirection: scrollDirection,
@@ -407,6 +415,7 @@ class CustomScrollView extends ScrollView {
     shrinkWrap: shrinkWrap,
     cacheExtent: cacheExtent,
     semanticChildCount: semanticChildCount,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// The slivers to place inside the viewport.
@@ -439,6 +448,7 @@ abstract class BoxScrollView extends ScrollView {
     this.padding,
     double cacheExtent,
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : super(
     key: key,
     scrollDirection: scrollDirection,
@@ -449,6 +459,7 @@ abstract class BoxScrollView extends ScrollView {
     shrinkWrap: shrinkWrap,
     cacheExtent: cacheExtent,
     semanticChildCount: semanticChildCount,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// The amount of space by which to inset the children.
@@ -739,6 +750,7 @@ class ListView extends BoxScrollView {
     double cacheExtent,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : childrenDelegate = SliverChildListDelegate(
          children,
          addAutomaticKeepAlives: addAutomaticKeepAlives,
@@ -755,6 +767,7 @@ class ListView extends BoxScrollView {
     padding: padding,
     cacheExtent: cacheExtent,
     semanticChildCount: semanticChildCount ?? children.length,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// Creates a scrollable, linear array of widgets that are created on demand.
@@ -800,6 +813,7 @@ class ListView extends BoxScrollView {
     bool addSemanticIndexes = true,
     double cacheExtent,
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : childrenDelegate = SliverChildBuilderDelegate(
          itemBuilder,
          childCount: itemCount,
@@ -817,6 +831,7 @@ class ListView extends BoxScrollView {
     padding: padding,
     cacheExtent: cacheExtent,
     semanticChildCount: semanticChildCount ?? itemCount,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// Creates a fixed-length scrollable linear array of list "items" separated
@@ -1250,6 +1265,7 @@ class GridView extends BoxScrollView {
     @required this.childrenDelegate,
     double cacheExtent,
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : assert(gridDelegate != null),
        assert(childrenDelegate != null),
        super(
@@ -1263,6 +1279,7 @@ class GridView extends BoxScrollView {
          padding: padding,
          cacheExtent: cacheExtent,
          semanticChildCount: semanticChildCount,
+         dragStartBehavior: dragStartBehavior,
        );
 
   /// Creates a scrollable, 2D array of widgets with a fixed number of tiles in
@@ -1298,6 +1315,7 @@ class GridView extends BoxScrollView {
     double cacheExtent,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : gridDelegate = SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: crossAxisCount,
          mainAxisSpacing: mainAxisSpacing,
@@ -1320,6 +1338,7 @@ class GridView extends BoxScrollView {
     padding: padding,
     cacheExtent: cacheExtent,
     semanticChildCount: semanticChildCount ?? children.length,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// Creates a scrollable, 2D array of widgets with tiles that each have a
@@ -1354,6 +1373,7 @@ class GridView extends BoxScrollView {
     bool addSemanticIndexes = true,
     List<Widget> children = const <Widget>[],
     int semanticChildCount,
+    DragStartBehavior dragStartBehavior = DragStartBehavior.start,
   }) : gridDelegate = SliverGridDelegateWithMaxCrossAxisExtent(
          maxCrossAxisExtent: maxCrossAxisExtent,
          mainAxisSpacing: mainAxisSpacing,
@@ -1375,6 +1395,7 @@ class GridView extends BoxScrollView {
     shrinkWrap: shrinkWrap,
     padding: padding,
     semanticChildCount: semanticChildCount ?? children.length,
+    dragStartBehavior: dragStartBehavior,
   );
 
   /// A delegate that controls the layout of the children within the [GridView].

packages/flutter/lib/src/widgets/scrollable.dart

@@ -81,7 +81,9 @@ class Scrollable extends StatefulWidget {
     @required this.viewportBuilder,
     this.excludeFromSemantics = false,
     this.semanticChildCount,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(axisDirection != null),
+       assert(dragStartBehavior != null),
        assert(viewportBuilder != null),
        assert(excludeFromSemantics != null),
        super (key: key);
@@ -180,6 +182,25 @@ class Scrollable extends StatefulWidget {
   ///  * [SemanticsConfiguration.scrollChildCount], the corresponding semantics property.
   final int semanticChildCount;
 
+  /// {@template flutter.widgets.scrollable.dragStartBehavior}
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], scrolling drag behavior will
+  /// begin upon the detection of a drag gesture. If set to
+  /// [DragStartBehavior.down] it will begin when a down event is first detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  /// {@endtemplate}
+  final DragStartBehavior dragStartBehavior;
+
   /// The axis along which the scroll view scrolls.
   ///
   /// Determined by the [axisDirection].
@@ -391,7 +412,8 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
                   ..onCancel = _handleDragCancel
                   ..minFlingDistance = _physics?.minFlingDistance
                   ..minFlingVelocity = _physics?.minFlingVelocity
-                  ..maxFlingVelocity = _physics?.maxFlingVelocity;
+                  ..maxFlingVelocity = _physics?.maxFlingVelocity
+                  ..dragStartBehavior = widget.dragStartBehavior;
               },
             ),
           };
@@ -409,7 +431,8 @@ class ScrollableState extends State<Scrollable> with TickerProviderStateMixin
                   ..onCancel = _handleDragCancel
                   ..minFlingDistance = _physics?.minFlingDistance
                   ..minFlingVelocity = _physics?.minFlingVelocity
-                  ..maxFlingVelocity = _physics?.maxFlingVelocity;
+                  ..maxFlingVelocity = _physics?.maxFlingVelocity
+                  ..dragStartBehavior = widget.dragStartBehavior;
               },
             ),
           };

packages/flutter/lib/src/widgets/single_child_scroll_view.dart

@@ -5,6 +5,7 @@
 import 'dart:math' as math;
 
 import 'package:flutter/rendering.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'basic.dart';
 import 'framework.dart';
@@ -192,7 +193,9 @@ class SingleChildScrollView extends StatelessWidget {
     this.physics,
     this.controller,
     this.child,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : assert(scrollDirection != null),
+       assert(dragStartBehavior != null),
        assert(!(controller != null && primary == true),
           'Primary ScrollViews obtain their ScrollController via inheritance from a PrimaryScrollController widget. '
           'You cannot both set primary to true and pass an explicit controller.'
@@ -259,6 +262,9 @@ class SingleChildScrollView extends StatelessWidget {
   /// {@macro flutter.widgets.child}
   final Widget child;
 
+  /// {@macro flutter.widgets.scrollable.dragStartBehavior}
+  final DragStartBehavior dragStartBehavior;
+
   AxisDirection _getDirection(BuildContext context) {
     return getAxisDirectionFromAxisReverseAndDirectionality(context, scrollDirection, reverse);
   }
@@ -273,6 +279,7 @@ class SingleChildScrollView extends StatelessWidget {
         ? PrimaryScrollController.of(context)
         : controller;
     final Scrollable scrollable = Scrollable(
+      dragStartBehavior: dragStartBehavior,
       axisDirection: axisDirection,
       controller: scrollController,
       physics: physics,

packages/flutter/lib/src/widgets/text_selection.dart

@@ -8,6 +8,7 @@ import 'package:flutter/gestures.dart' show kDoubleTapTimeout, kDoubleTapSlop;
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'basic.dart';
 import 'container.dart';
@@ -229,6 +230,7 @@ class TextSelectionOverlay {
     @required this.renderObject,
     this.selectionControls,
     this.selectionDelegate,
+    this.dragStartBehavior = DragStartBehavior.start,
   }): assert(value != null),
       assert(context != null),
       _value = value {
@@ -263,6 +265,23 @@ class TextSelectionOverlay {
   /// text field.
   final TextSelectionDelegate selectionDelegate;
 
+  /// Determines the way that drag start behavior is handled.
+  ///
+  /// If set to [DragStartBehavior.start], handle drag behavior will
+  /// begin upon the detection of a drag gesture. If set to
+  /// [DragStartBehavior.down] it will begin when a down event is first detected.
+  ///
+  /// In general, setting this to [DragStartBehavior.start] will make drag
+  /// animation smoother and setting it to [DragStartBehavior.down] will make
+  /// drag behavior feel slightly more reactive.
+  ///
+  /// By default, the drag start behavior is [DragStartBehavior.start].
+  ///
+  /// See also:
+  ///
+  ///  * [DragGestureRecognizer.dragStartBehavior], which gives an example for the different behaviors.
+  final DragStartBehavior dragStartBehavior;
+
   /// Controls the fade-in animations.
   static const Duration _fadeDuration = Duration(milliseconds: 150);
   AnimationController _handleController;
@@ -365,9 +384,8 @@ class TextSelectionOverlay {
 
   Widget _buildHandle(BuildContext context, _TextSelectionHandlePosition position) {
     if ((_selection.isCollapsed && position == _TextSelectionHandlePosition.end) ||
-        selectionControls == null)
+         selectionControls == null)
       return Container(); // hide the second handle when collapsed
-
     return FadeTransition(
       opacity: _handleOpacity,
       child: _TextSelectionHandleOverlay(
@@ -378,6 +396,7 @@ class TextSelectionOverlay {
         selection: _selection,
         selectionControls: selectionControls,
         position: position,
+        dragStartBehavior: dragStartBehavior,
       )
     );
   }
@@ -447,7 +466,8 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
     @required this.renderObject,
     @required this.onSelectionHandleChanged,
     @required this.onSelectionHandleTapped,
-    @required this.selectionControls
+    @required this.selectionControls,
+    this.dragStartBehavior = DragStartBehavior.start,
   }) : super(key: key);
 
   final TextSelection selection;
@@ -457,6 +477,7 @@ class _TextSelectionHandleOverlay extends StatefulWidget {
   final ValueChanged<TextSelection> onSelectionHandleChanged;
   final VoidCallback onSelectionHandleTapped;
   final TextSelectionControls selectionControls;
+  final DragStartBehavior dragStartBehavior;
 
   @override
   _TextSelectionHandleOverlayState createState() => _TextSelectionHandleOverlayState();
@@ -528,6 +549,7 @@ class _TextSelectionHandleOverlayState extends State<_TextSelectionHandleOverlay
       link: widget.layerLink,
       showWhenUnlinked: false,
       child: GestureDetector(
+        dragStartBehavior: widget.dragStartBehavior,
         onPanStart: _handleDragStart,
         onPanUpdate: _handleDragUpdate,
         onTap: _handleTap,

packages/flutter/test/cupertino/switch_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/cupertino.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart';
 
 void main() {
   testWidgets('Switch can toggle on tap', (WidgetTester tester) async {
@@ -18,6 +19,7 @@ void main() {
               child: CupertinoSwitch(
                 key: switchKey,
                 value: value,
+                dragStartBehavior: DragStartBehavior.down,
                 onChanged: (bool newValue) {
                   setState(() {
                     value = newValue;
@@ -46,6 +48,7 @@ void main() {
             return Center(
               child: CupertinoSwitch(
                 value: value,
+                dragStartBehavior: DragStartBehavior.down,
                 onChanged: (bool newValue) {
                   setState(() {
                     value = newValue;
@@ -79,6 +82,88 @@ void main() {
     expect(value, isFalse);
   });
 
+  testWidgets('Switch can drag with dragStartBehavior', (WidgetTester tester) async {
+    bool value = false;
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Center(
+              child: CupertinoSwitch(
+                value: value,
+                dragStartBehavior: DragStartBehavior.down,
+                onChanged: (bool newValue) {
+                  setState(() {
+                    value = newValue;
+                  });
+                },
+              ),
+            );
+          },
+        ),
+      ),
+    );
+
+    expect(value, isFalse);
+    await tester.drag(find.byType(CupertinoSwitch), const Offset(-30.0, 0.0));
+    expect(value, isFalse);
+
+    await tester.drag(find.byType(CupertinoSwitch), const Offset(30.0, 0.0));
+    expect(value, isTrue);
+    await tester.pump();
+    await tester.drag(find.byType(CupertinoSwitch), const Offset(30.0, 0.0));
+    expect(value, isTrue);
+    await tester.pump();
+    await tester.drag(find.byType(CupertinoSwitch), const Offset(-30.0, 0.0));
+    expect(value, isFalse);
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Center(
+              child: CupertinoSwitch(
+                value: value,
+                dragStartBehavior: DragStartBehavior.start,
+                onChanged: (bool newValue) {
+                  setState(() {
+                    value = newValue;
+                  });
+                },
+              ),
+            );
+          },
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    final Rect switchRect = tester.getRect(find.byType(CupertinoSwitch));
+
+    TestGesture gesture = await tester.startGesture(switchRect.center);
+    // We have to execute the drag in two frames because the first update will
+    // just set the start position.
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    expect(value, isTrue);
+    await gesture.up();
+    await tester.pump();
+
+    gesture = await tester.startGesture(switchRect.center);
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    expect(value, isTrue);
+    await gesture.up();
+    await tester.pump();
+
+    gesture = await tester.startGesture(switchRect.center);
+    await gesture.moveBy(const Offset(-20.0, 0.0));
+    await gesture.moveBy(const Offset(-20.0, 0.0));
+    expect(value, isFalse);
+  });
+
   testWidgets('Switch can drag (RTL)', (WidgetTester tester) async {
     bool value = false;
 
@@ -90,6 +175,7 @@ void main() {
             return Center(
               child: CupertinoSwitch(
                 value: value,
+                dragStartBehavior: DragStartBehavior.down,
                 onChanged: (bool newValue) {
                   setState(() {
                     value = newValue;

packages/flutter/test/gestures/drag_test.dart

@@ -58,8 +58,7 @@ void main() {
     tester.route(pointer.move(const Offset(20.0, 30.0))); // moved 10 horizontally and 20 vertically which is 22 total
     expect(didStartPan, isTrue); // 22 > 18
     didStartPan = false;
-    expect(updatedScrollDelta, const Offset(10.0, 20.0));
+    expect(updatedScrollDelta, null);
-    updatedScrollDelta = null;
     expect(didEndPan, isFalse);
     expect(didTap, isFalse);
 
@@ -82,7 +81,7 @@ void main() {
   });
 
   testGesture('Should recognize drag', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     bool didStartDrag = false;
     drag.onStart = (_) {
@@ -135,7 +134,7 @@ void main() {
   });
 
   testGesture('Should report original timestamps', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     Duration startTimestamp;
     drag.onStart = (DragStartDetails details) {
@@ -165,9 +164,98 @@ void main() {
     drag.dispose();
   });
 
-  testGesture('Drag with multiple pointers', (GestureTester tester) {
+  testGesture('Should report most recent point to onStart by default', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag1 = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
-    final VerticalDragGestureRecognizer drag2 = VerticalDragGestureRecognizer();
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer();
+
+    Offset positionAtOnStart;
+    drag.onStart = (DragStartDetails details) {
+      positionAtOnStart = details.globalPosition;
+    };
+
+    final TestPointer pointer = TestPointer(5);
+    final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
+    drag.addPointer(down);
+    competingDrag.addPointer(down);
+    tester.closeArena(5);
+    tester.route(down);
+
+    tester.route(pointer.move(const Offset(30.0, 0.0)));
+    drag.dispose();
+    competingDrag.dispose();
+
+    expect(positionAtOnStart, const Offset(30.0, 00.0));
+  });
+
+  testGesture('Should report most recent point to onStart with a start configuration', (GestureTester tester) {
+    final HorizontalDragGestureRecognizer drag =
+    HorizontalDragGestureRecognizer();
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer();
+
+    Offset positionAtOnStart;
+    drag.onStart = (DragStartDetails details) {
+      positionAtOnStart = details.globalPosition;
+    };
+    Offset updateOffset;
+    drag.onUpdate = (DragUpdateDetails details) {
+      updateOffset = details.globalPosition;
+    };
+
+    final TestPointer pointer = TestPointer(5);
+    final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
+    drag.addPointer(down);
+    competingDrag.addPointer(down);
+    tester.closeArena(5);
+    tester.route(down);
+
+    tester.route(pointer.move(const Offset(30.0, 0.0)));
+    drag.dispose();
+    competingDrag.dispose();
+
+    expect(positionAtOnStart, const Offset(30.0, 0.0));
+    expect(updateOffset, null);
+  });
+
+  testGesture('Should report initial down point to onStart with a down configuration', (GestureTester tester) {
+    final HorizontalDragGestureRecognizer drag =
+    HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
+
+    Offset positionAtOnStart;
+    drag.onStart = (DragStartDetails details) {
+      positionAtOnStart = details.globalPosition;
+    };
+    Offset updateOffset;
+    Offset updateDelta;
+    drag.onUpdate = (DragUpdateDetails details) {
+      updateOffset = details.globalPosition;
+      updateDelta = details.delta;
+    };
+
+    final TestPointer pointer = TestPointer(5);
+    final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
+    drag.addPointer(down);
+    competingDrag.addPointer(down);
+    tester.closeArena(5);
+    tester.route(down);
+
+    tester.route(pointer.move(const Offset(30.0, 0.0)));
+    drag.dispose();
+    competingDrag.dispose();
+
+    expect(positionAtOnStart, const Offset(10.0, 10.0));
+
+    // The drag is horizontal so we're going to ignore the vertical delta position
+    // when calculating the new global position.
+    expect(updateOffset, const Offset(30.0, 10.0));
+    expect(updateDelta, const Offset(20.0, 0.0));
+  });
+
+  testGesture('Drag with multiple pointers in down behavior', (GestureTester tester) {
+    final HorizontalDragGestureRecognizer drag1 =
+    HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
+    final VerticalDragGestureRecognizer drag2 =
+    VerticalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     final List<String> log = <String>[];
     drag1.onDown = (_) { log.add('drag1-down'); };
@@ -235,7 +323,7 @@ void main() {
   });
 
   testGesture('Clamp max velocity', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     Velocity velocity;
     double primaryVelocity;
@@ -269,7 +357,7 @@ void main() {
   });
 
   testGesture('Synthesized pointer events are ignored for velocity tracking', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     Velocity velocity;
     drag.onEnd = (DragEndDetails details) {
@@ -303,7 +391,7 @@ void main() {
   /// Checks that quick flick gestures with 1 down, 2 move and 1 up pointer
   /// events still have a velocity
   testGesture('Quick flicks have velocity', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     Velocity velocity;
     drag.onEnd = (DragEndDetails details) {
@@ -333,16 +421,18 @@ void main() {
   });
 
   testGesture('Should recognize drag', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
     bool didStartDrag = false;
     drag.onStart = (_) {
       didStartDrag = true;
     };
 
-    double updatedDelta;
+    Offset updateDelta;
+    double updatePrimaryDelta;
     drag.onUpdate = (DragUpdateDetails details) {
-      updatedDelta = details.primaryDelta;
+      updateDelta = details.delta;
+      updatePrimaryDelta = details.primaryDelta;
     };
 
     bool didEndDrag = false;
@@ -354,31 +444,39 @@ void main() {
     final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
     drag.addPointer(down);
     tester.closeArena(5);
+
     expect(didStartDrag, isFalse);
-    expect(updatedDelta, isNull);
+    expect(updateDelta, isNull);
+    expect(updatePrimaryDelta, isNull);
     expect(didEndDrag, isFalse);
 
     tester.route(down);
     expect(didStartDrag, isTrue);
-    expect(updatedDelta, isNull);
+    expect(updateDelta, isNull);
+    expect(updatePrimaryDelta, isNull);
     expect(didEndDrag, isFalse);
-
-    tester.route(pointer.move(const Offset(20.0, 25.0)));
-    expect(didStartDrag, isTrue);
     didStartDrag = false;
-    expect(updatedDelta, 10.0);
-    updatedDelta = null;
-    expect(didEndDrag, isFalse);
 
     tester.route(pointer.move(const Offset(20.0, 25.0)));
     expect(didStartDrag, isFalse);
-    expect(updatedDelta, 0.0);
+    expect(updateDelta, const Offset(10.0, 0.0));
-    updatedDelta = null;
+    expect(updatePrimaryDelta, 10.0);
     expect(didEndDrag, isFalse);
+    updateDelta = null;
+    updatePrimaryDelta = null;
+
+    tester.route(pointer.move(const Offset(20.0, 25.0)));
+    expect(didStartDrag, isFalse);
+    expect(updateDelta, const Offset(0.0, 0.0));
+    expect(updatePrimaryDelta, 0.0);
+    expect(didEndDrag, isFalse);
+    updateDelta = null;
+    updatePrimaryDelta = null;
 
     tester.route(pointer.up());
     expect(didStartDrag, isFalse);
-    expect(updatedDelta, isNull);
+    expect(updateDelta, isNull);
+    expect(updatePrimaryDelta, isNull);
     expect(didEndDrag, isTrue);
     didEndDrag = false;
 
@@ -386,21 +484,36 @@ void main() {
   });
 
   testGesture('Should recognize drag', (GestureTester tester) {
-    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
 
-    Offset newGlobalPosition;
+    Offset latestGlobalPosition;
+    drag.onStart = (DragStartDetails details) {
+      latestGlobalPosition = details.globalPosition;
+    };
+    Offset latestDelta;
     drag.onUpdate = (DragUpdateDetails details) {
-      newGlobalPosition = details.globalPosition;
+      latestGlobalPosition = details.globalPosition;
+      latestDelta = details.delta;
     };
 
     final TestPointer pointer = TestPointer(5);
     final PointerDownEvent down = pointer.down(const Offset(10.0, 10.0));
     drag.addPointer(down);
-    tester.route(pointer.move(const Offset(20.0, 25.0)));
     tester.closeArena(5);
+
     tester.route(down);
-    expect(newGlobalPosition, const Offset(20.0, 10.0));
+    expect(latestGlobalPosition, const Offset(10.0, 10.0));
+    expect(latestDelta, isNull);
+
+    tester.route(pointer.move(const Offset(20.0, 25.0)));
+    expect(latestGlobalPosition, const Offset(20.0, 25.0));
+    expect(latestDelta, const Offset(10.0, 0.0));
+
+    tester.route(pointer.move(const Offset(0.0, 45.0)));
+    expect(latestGlobalPosition, const Offset(0.0, 45.0));
+    expect(latestDelta, const Offset(-20.0, 0.0));
+
     tester.route(pointer.up());
     drag.dispose();
   });
-}
+}

packages/flutter/test/material/date_picker_test.dart

@@ -8,6 +8,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../widgets/semantics_tester.dart';
 import 'feedback_tester.dart';
@@ -46,8 +47,10 @@ void _tests() {
             return Container(
               width: 400.0,
               child: SingleChildScrollView(
+                dragStartBehavior: DragStartBehavior.down,
                 child: Material(
                   child: MonthPicker(
+                    dragStartBehavior: DragStartBehavior.down,
                     firstDate: DateTime(0),
                     lastDate: DateTime(9999),
                     key: _datePickerKey,
@@ -63,7 +66,7 @@ void _tests() {
             );
           },
         ),
-      )
+      ),
     );
 
     expect(_selectedDate, equals(DateTime(2016, DateTime.july, 26)));

packages/flutter/test/material/ink_well_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart';
 
 import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
@@ -164,6 +165,7 @@ void main() {
               link: LayerLink(),
               child: ListView(
                 addAutomaticKeepAlives: keepAlive,
+                dragStartBehavior: DragStartBehavior.down,
                 children: <Widget>[
                   Container(height: 500.0, child: InkWell(onTap: () { }, child: const Placeholder())),
                   Container(height: 500.0),

packages/flutter/test/material/paginated_data_table_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'data_table_test_utils.dart';
 
@@ -248,26 +249,29 @@ void main() {
 
   testWidgets('PaginatedDataTable footer scrolls', (WidgetTester tester) async {
     final TestDataSource source = TestDataSource();
-    await tester.pumpWidget(MaterialApp(
+    await tester.pumpWidget(
-      home: Align(
+      MaterialApp(
-        alignment: Alignment.topLeft,
+        home: Align(
-        child: SizedBox(
+          alignment: Alignment.topLeft,
-          width: 100.0,
+          child: SizedBox(
-          child: PaginatedDataTable(
+            width: 100.0,
-            header: const Text('HEADER'),
+            child: PaginatedDataTable(
-            source: source,
+              header: const Text('HEADER'),
-            rowsPerPage: 5,
+              source: source,
-            availableRowsPerPage: const <int>[ 5 ],
+              rowsPerPage: 5,
-            onRowsPerPageChanged: (int rowsPerPage) { },
+              dragStartBehavior: DragStartBehavior.down,
-            columns: const <DataColumn>[
+              availableRowsPerPage: const <int>[ 5 ],
-              DataColumn(label: Text('COL1')),
+              onRowsPerPageChanged: (int rowsPerPage) { },
-              DataColumn(label: Text('COL2')),
+              columns: const <DataColumn>[
-              DataColumn(label: Text('COL3')),
+                DataColumn(label: Text('COL1')),
-            ],
+                DataColumn(label: Text('COL2')),
+                DataColumn(label: Text('COL3')),
+              ],
+            ),
           ),
         ),
       ),
-    ));
+    );
     expect(find.text('Rows per page:'), findsOneWidget);
     expect(tester.getTopLeft(find.text('Rows per page:')).dx, lessThan(0.0)); // off screen
     await tester.dragFrom(

packages/flutter/test/material/scaffold_test.dart

@@ -6,6 +6,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../widgets/semantics_tester.dart';
 
@@ -201,6 +202,7 @@ void main() {
           drawer: Drawer(
             key: drawerKey,
             child: ListView(
+              dragStartBehavior: DragStartBehavior.down,
               controller: scrollOffset,
               children: List<Widget>.generate(10,
                 (int index) => SizedBox(height: 100.0, child: Text('D$index'))
@@ -630,6 +632,7 @@ void main() {
               viewInsets: EdgeInsets.only(bottom: 200.0),
             ),
             child: Scaffold(
+              drawerDragStartBehavior: DragStartBehavior.down,
               appBar: PreferredSize(
                 preferredSize: const Size(11.0, 13.0),
                 child: Container(

packages/flutter/test/material/switch_test.dart

@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart';
 
 import '../rendering/mock_canvas.dart';
 import '../widgets/semantics_tester.dart';
@@ -25,6 +25,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   key: switchKey,
                   value: value,
                   onChanged: (bool newValue) {
@@ -54,6 +55,7 @@ void main() {
           child: Material(
             child: Center(
               child: Switch(
+                dragStartBehavior: DragStartBehavior.down,
                 value: true,
                 onChanged: (bool newValue) {},
               ),
@@ -73,6 +75,7 @@ void main() {
           child: Material(
             child: Center(
               child: Switch(
+                dragStartBehavior: DragStartBehavior.down,
                 value: true,
                 onChanged: (bool newValue) {},
               ),
@@ -96,6 +99,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   value: value,
                   onChanged: (bool newValue) {
                     setState(() {
@@ -131,6 +135,93 @@ void main() {
     expect(value, isFalse);
   });
 
+  testWidgets('Switch can drag with dragStartBehavior', (WidgetTester tester) async {
+    bool value = false;
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Material(
+              child: Center(
+                child: Switch(
+                    dragStartBehavior: DragStartBehavior.down,
+                    value: value,
+                    onChanged: (bool newValue) {
+                      setState(() {
+                        value = newValue;
+                      }
+                    );
+                  }
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+
+    expect(value, isFalse);
+    await tester.drag(find.byType(Switch), const Offset(-30.0, 0.0));
+    expect(value, isFalse);
+
+    await tester.drag(find.byType(Switch), const Offset(30.0, 0.0));
+    expect(value, isTrue);
+    await tester.pump();
+    await tester.drag(find.byType(Switch), const Offset(30.0, 0.0));
+    expect(value, isTrue);
+    await tester.pump();
+    await tester.drag(find.byType(Switch), const Offset(-30.0, 0.0));
+    expect(value, isFalse);
+
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Material(
+              child: Center(
+                child: Switch(
+                    dragStartBehavior: DragStartBehavior.start,
+                    value: value,
+                    onChanged: (bool newValue) {
+                      setState(() {
+                        value = newValue;
+                      });
+                    }
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+    await tester.pumpAndSettle();
+    final Rect switchRect = tester.getRect(find.byType(Switch));
+
+    TestGesture gesture = await tester.startGesture(switchRect.center);
+    // We have to execute the drag in two frames because the first update will
+    // just set the start position.
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    expect(value, isTrue);
+    await gesture.up();
+    await tester.pump();
+
+    gesture = await tester.startGesture(switchRect.center);
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    expect(value, isTrue);
+    await gesture.up();
+    await tester.pump();
+
+    gesture = await tester.startGesture(switchRect.center);
+    await gesture.moveBy(const Offset(-20.0, 0.0));
+    await gesture.moveBy(const Offset(-20.0, 0.0));
+    expect(value, isFalse);
+  });
+
   testWidgets('Switch can drag (RTL)', (WidgetTester tester) async {
     bool value = false;
 
@@ -142,6 +233,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   value: value,
                   onChanged: (bool newValue) {
                     setState(() {
@@ -185,6 +277,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   value: value,
                   onChanged: (bool newValue) {
                     setState(() {
@@ -306,6 +399,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   value: value,
                   onChanged: (bool newValue) {
                     setState(() {
@@ -365,6 +459,7 @@ void main() {
             return Material(
               child: Center(
                 child: Switch(
+                  dragStartBehavior: DragStartBehavior.down,
                   value: value,
                   onChanged: (bool newValue) {
                     setState(() {

packages/flutter/test/material/text_field_test.dart

@@ -12,6 +12,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../widgets/semantics_tester.dart';
 import 'feedback_tester.dart';
@@ -501,9 +502,12 @@ void main() {
     final TextEditingController controller = TextEditingController();
 
     await tester.pumpWidget(
-      overlay(
+      MaterialApp(
-        child: TextField(
+        home: Material(
-          controller: controller,
+          child: TextField(
+            dragStartBehavior: DragStartBehavior.down,
+            controller: controller,
+          ),
         ),
       ),
     );
@@ -542,7 +546,7 @@ void main() {
     await tester.pump();
 
     expect(controller.selection.baseOffset, selection.baseOffset);
-    expect(controller.selection.extentOffset, selection.extentOffset+2);
+    expect(controller.selection.extentOffset, selection.extentOffset);
 
     // Drag the left handle 2 letters to the left.
     handlePos = endpoints[0].point + const Offset(-1.0, 1.0);
@@ -554,8 +558,8 @@ void main() {
     await gesture.up();
     await tester.pump();
 
-    expect(controller.selection.baseOffset, selection.baseOffset-2);
+    expect(controller.selection.baseOffset, selection.baseOffset);
-    expect(controller.selection.extentOffset, selection.extentOffset+2);
+    expect(controller.selection.extentOffset, selection.extentOffset);
   });
 
   testWidgets('Can use selection toolbar', (WidgetTester tester) async {
@@ -826,6 +830,7 @@ void main() {
     await tester.pumpWidget(
       overlay(
         child: TextField(
+          dragStartBehavior: DragStartBehavior.down,
           controller: controller,
           style: const TextStyle(color: Colors.black, fontSize: 34.0),
           maxLines: 3,
@@ -909,6 +914,7 @@ void main() {
     await tester.pumpWidget(
       overlay(
         child: TextField(
+          dragStartBehavior: DragStartBehavior.down,
           key: textFieldKey,
           controller: controller,
           style: const TextStyle(color: Colors.black, fontSize: 34.0),

packages/flutter/test/widgets/automatic_keep_alive_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 class Leaf extends StatefulWidget {
   const Leaf({ Key key, this.child }) : super(key: key);
@@ -476,6 +477,7 @@ void main() {
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: ListView.builder(
+        dragStartBehavior: DragStartBehavior.down,
         addSemanticIndexes: false,
         itemCount: 50,
         itemBuilder: (BuildContext context, int index){

packages/flutter/test/widgets/dismissible_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 const double itemExtent = 100.0;
 Axis scrollDirection = Axis.vertical;
@@ -21,6 +22,7 @@ Widget buildTest({ double startToEndThreshold, TextDirection textDirection = Tex
       builder: (BuildContext context, StateSetter setState) {
         Widget buildDismissibleItem(int item) {
           return Dismissible(
+            dragStartBehavior: DragStartBehavior.down,
             key: ValueKey<int>(item),
             direction: dismissDirection,
             onDismissed: (DismissDirection direction) {
@@ -49,6 +51,7 @@ Widget buildTest({ double startToEndThreshold, TextDirection textDirection = Tex
         return Container(
           padding: const EdgeInsets.all(10.0),
           child: ListView(
+            dragStartBehavior: DragStartBehavior.down,
             scrollDirection: scrollDirection,
             itemExtent: itemExtent,
             children: <int>[0, 1, 2, 3, 4]
@@ -199,6 +202,7 @@ class Test1215DismissibleWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Dismissible(
+      dragStartBehavior: DragStartBehavior.down,
       key: ObjectKey(text),
       child: AspectRatio(
         aspectRatio: 1.0,

packages/flutter/test/widgets/draggable_test.dart

@@ -383,6 +383,7 @@ void main() {
 
     await tester.pumpWidget(MaterialApp(
       home: ListView(
+        dragStartBehavior: DragStartBehavior.down,
         children: <Widget>[
           DragTarget<int>(
             builder: (BuildContext context, List<int> data, List<dynamic> rejects) {
@@ -489,6 +490,7 @@ void main() {
 
     await tester.pumpWidget(MaterialApp(
       home: ListView(
+        dragStartBehavior: DragStartBehavior.down,
         scrollDirection: Axis.horizontal,
         children: <Widget>[
           DragTarget<int>(

packages/flutter/test/widgets/drawer_test.dart

@@ -9,6 +9,7 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'semantics_tester.dart';
 
@@ -82,6 +83,7 @@ void main() {
     await tester.pumpWidget(
       MaterialApp(
         home: Scaffold(
+          drawerDragStartBehavior: DragStartBehavior.down,
           key: scaffoldKey,
           drawer: Drawer(
             child: ListView(
@@ -134,6 +136,7 @@ void main() {
         home: Directionality(
           textDirection: TextDirection.rtl,
           child: Scaffold(
+            drawerDragStartBehavior: DragStartBehavior.down,
             key: scaffoldKey,
             drawer: Drawer(
               child: ListView(

packages/flutter/test/widgets/gesture_detector_test.dart

@@ -64,6 +64,7 @@ void main() {
     const Offset upLocation = Offset(10.0, 50.0); // must be far enough to be more than kTouchSlop
 
     final Widget widget = GestureDetector(
+      dragStartBehavior: DragStartBehavior.down,
       onVerticalDragUpdate: (DragUpdateDetails details) { dragDistance += details.primaryDelta; },
       onVerticalDragEnd: (DragEndDetails details) { gestureCount += 1; },
       onHorizontalDragUpdate: (DragUpdateDetails details) { fail('gesture should not match'); },

packages/flutter/test/widgets/grid_view_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../rendering/mock_canvas.dart';
 import 'states.dart';
@@ -14,6 +15,7 @@ void main() {
       Directionality(
         textDirection: TextDirection.ltr,
         child: GridView.count(
+          dragStartBehavior: DragStartBehavior.down,
           crossAxisCount: 4,
           children: const <Widget>[],
         ),
@@ -28,9 +30,11 @@ void main() {
       Directionality(
         textDirection: TextDirection.ltr,
         child: GridView.count(
+          dragStartBehavior: DragStartBehavior.down,
           crossAxisCount: 4,
           children: kStates.map<Widget>((String state) {
             return GestureDetector(
+              dragStartBehavior: DragStartBehavior.down,
               onTap: () {
                 log.add(state);
               },
@@ -99,9 +103,11 @@ void main() {
       Directionality(
         textDirection: TextDirection.ltr,
         child: GridView.extent(
+          dragStartBehavior: DragStartBehavior.down,
           maxCrossAxisExtent: 200.0,
           children: kStates.map<Widget>((String state) {
             return GestureDetector(
+              dragStartBehavior: DragStartBehavior.down,
               onTap: () {
                 log.add(state);
               },

packages/flutter/test/widgets/heroes_test.dart

@@ -1373,8 +1373,11 @@ void main() {
     expect(find.byKey(secondKey), isOnstage);
     expect(find.byKey(secondKey), isInCard);
 
-    final TestGesture gesture = await tester.startGesture(const Offset(5.0, 200.0));
+    final TestGesture  gesture = await tester.startGesture(const Offset(5.0, 200.0));
-    await gesture.moveBy(const Offset(200.0, 0.0));
+    await gesture.moveBy(const Offset(20.0, 0.0));
+    await gesture.moveBy(const Offset(180.0, 0.0));
+    await gesture.up();
+    await tester.pump();
 
     await tester.pump();
 

packages/flutter/test/widgets/listview_end_append_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 void main() {
   testWidgets('ListView.builder() fixed itemExtent, scroll to end, append, scroll', (WidgetTester tester) async {
@@ -13,6 +14,7 @@ void main() {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: ListView.builder(
+          dragStartBehavior: DragStartBehavior.down,
           itemExtent: 200.0,
           itemCount: itemCount,
           itemBuilder: (BuildContext context, int index) => Text('item $index'),
@@ -40,6 +42,7 @@ void main() {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: ListView.builder(
+          dragStartBehavior: DragStartBehavior.down,
           itemCount: itemCount,
           itemBuilder: (BuildContext context, int index) {
             return SizedBox(

packages/flutter/test/widgets/nested_scroll_view_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import '../rendering/mock_canvas.dart';
 
@@ -34,9 +35,11 @@ Widget buildTest({ ScrollController controller, String title ='TTTTTTTT' }) {
       child: MediaQuery(
         data: const MediaQueryData(),
         child: Scaffold(
+          drawerDragStartBehavior: DragStartBehavior.down,
           body: DefaultTabController(
             length: 4,
             child: NestedScrollView(
+              dragStartBehavior: DragStartBehavior.down,
               controller: controller,
               headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
                 return <Widget>[
@@ -79,6 +82,7 @@ Widget buildTest({ ScrollController controller, String title ='TTTTTTTT' }) {
                     ],
                   ),
                   ListView(
+                    dragStartBehavior: DragStartBehavior.down,
                     children: <Widget>[
                       Container(
                         height: 100.0,
@@ -90,6 +94,7 @@ Widget buildTest({ ScrollController controller, String title ='TTTTTTTT' }) {
                     child: const Center(child: Text('ccc1')),
                   ),
                   ListView(
+                    dragStartBehavior: DragStartBehavior.down,
                     children: <Widget>[
                       Container(
                         height: 10000.0,
@@ -361,6 +366,7 @@ void main() {
         DefaultTabController(
           length: _tabs.length, // This is the number of tabs.
           child: NestedScrollView(
+            dragStartBehavior: DragStartBehavior.down,
             headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
               buildCount += 1; // THIS LINE IS NOT IN THE ORIGINAL -- ADDED FOR TEST
               // These are the slivers that show up in the "outer" scroll view.
@@ -390,12 +396,14 @@ void main() {
                     bottom: TabBar(
                       // These are the widgets to put in each tab in the tab bar.
                       tabs: _tabs.map<Widget>((String name) => Tab(text: name)).toList(),
+                      dragStartBehavior: DragStartBehavior.down,
                     ),
                   ),
                 ),
               ];
             },
             body: TabBarView(
+              dragStartBehavior: DragStartBehavior.down,
               // These are the contents of the tab views, below the tabs.
               children: _tabs.map<Widget>((String name) {
                 return SafeArea(
@@ -416,6 +424,7 @@ void main() {
                         // it allows the list to remember its scroll position when
                         // the tab view is not on the screen.
                         key: PageStorageKey<String>(name),
+                        dragStartBehavior: DragStartBehavior.down,
                         slivers: <Widget>[
                           SliverOverlapInjector(
                             // This is the flip side of the SliverOverlapAbsorber above.
@@ -590,6 +599,7 @@ void main() {
           child: DefaultTabController(
             length: 1,
             child: NestedScrollView(
+              dragStartBehavior: DragStartBehavior.down,
               headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
                 return <Widget>[
                   const SliverPersistentHeader(
@@ -598,6 +608,7 @@ void main() {
                 ];
               },
               body: SingleChildScrollView(
+                dragStartBehavior: DragStartBehavior.down,
                 child: Container(
                   height: 1000.0,
                   child: const Placeholder(key: key2),

packages/flutter/test/widgets/page_view_test.dart

@@ -6,6 +6,7 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'semantics_tester.dart';
 import 'states.dart';
@@ -19,8 +20,10 @@ void main() {
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: PageView(
+        dragStartBehavior: DragStartBehavior.down,
         children: kStates.map<Widget>((String state) {
           return GestureDetector(
+            dragStartBehavior: DragStartBehavior.down,
             onTap: () {
               log.add(state);
             },

packages/flutter/test/widgets/scroll_notification_test.dart

@@ -60,6 +60,7 @@ void main() {
         return false;
       },
       child: SingleChildScrollView(
+        dragStartBehavior: DragStartBehavior.down,
         child: SizedBox(
           height: 1200.0,
           child: NotificationListener<ScrollNotification>(
@@ -70,11 +71,14 @@ void main() {
             },
             child: Container(
               padding: const EdgeInsets.all(50.0),
-              child: const SingleChildScrollView(child: SizedBox(height: 1200.0))
+              child: const SingleChildScrollView(
-            )
+                child: SizedBox(height: 1200.0),
-          )
+                dragStartBehavior: DragStartBehavior.down,
-        )
+              ),
-      )
+            ),
+          ),
+        ),
+      ),
     ));
 
     final TestGesture gesture = await tester.startGesture(const Offset(100.0, 100.0));

packages/flutter/test/widgets/scroll_view_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 import 'package:flutter/material.dart';
 
 import 'states.dart';
@@ -16,6 +17,7 @@ void main() {
       Directionality(
         textDirection: TextDirection.ltr,
         child: ListView(
+          dragStartBehavior: DragStartBehavior.down,
           children: kStates.map<Widget>((String state) {
             return GestureDetector(
               onTap: () {
@@ -26,6 +28,7 @@ void main() {
                 color: const Color(0xFF0000FF),
                 child: Text(state),
               ),
+              dragStartBehavior: DragStartBehavior.down,
             );
           }).toList(),
         ),
@@ -54,6 +57,7 @@ void main() {
       return Directionality(
         textDirection: TextDirection.ltr,
         child: ListView(
+          dragStartBehavior: DragStartBehavior.down,
           children: kStates.take(n).map<Widget>((String state) {
             return Container(
               height: 200.0,
@@ -85,11 +89,13 @@ void main() {
       Directionality(
         textDirection: TextDirection.ltr,
         child: CustomScrollView(
+          dragStartBehavior: DragStartBehavior.down,
           slivers: <Widget>[
             SliverList(
               delegate: SliverChildListDelegate(
                 kStates.map<Widget>((String state) {
                   return GestureDetector(
+                    dragStartBehavior: DragStartBehavior.down,
                     onTap: () {
                       log.add(state);
                     },

packages/flutter/test/widgets/scrollable_fling_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 const TextStyle testFont = TextStyle(
   color: Color(0xFF00FF00),
@@ -19,6 +20,7 @@ Future<void> pumpTest(WidgetTester tester, TargetPlatform platform) async {
     home: Container(
       color: const Color(0xFF111111),
       child: ListView.builder(
+        dragStartBehavior: DragStartBehavior.down,
         itemBuilder: (BuildContext context, int index) {
           return Text('$index', style: testFont);
         },
@@ -64,7 +66,7 @@ void main() {
     await tester.pumpWidget(
       Directionality(
         textDirection: TextDirection.ltr,
-        child: ListView(children: textWidgets)
+        child: ListView(children: textWidgets, dragStartBehavior: DragStartBehavior.down)
       ),
     );
 
@@ -92,7 +94,7 @@ void main() {
     await tester.pumpWidget(
       Directionality(
         textDirection: TextDirection.ltr,
-        child: ListView(children: textWidgets)
+        child: ListView(children: textWidgets, dragStartBehavior: DragStartBehavior.down)
       ),
     );
 

packages/flutter/test/widgets/scrollable_list_hit_testing_test.dart

@@ -5,6 +5,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 const List<int> items = <int>[0, 1, 2, 3, 4, 5];
 
@@ -18,6 +19,7 @@ void main() {
           child: Container(
             height: 50.0,
             child: ListView(
+              dragStartBehavior: DragStartBehavior.down,
               itemExtent: 290.0,
               scrollDirection: Axis.horizontal,
               children: items.map<Widget>((int item) {
@@ -25,6 +27,7 @@ void main() {
                   child: GestureDetector(
                     onTap: () { tapped.add(item); },
                     child: Text('$item'),
+                    dragStartBehavior: DragStartBehavior.down,
                   ),
                 );
               }).toList(),
@@ -60,6 +63,7 @@ void main() {
           child: Container(
             width: 50.0,
             child: ListView(
+              dragStartBehavior: DragStartBehavior.down,
               itemExtent: 290.0,
               scrollDirection: Axis.vertical,
               children: items.map<Widget>((int item) {
@@ -67,6 +71,7 @@ void main() {
                   child: GestureDetector(
                     onTap: () { tapped.add(item); },
                     child: Text('$item'),
+                    dragStartBehavior: DragStartBehavior.down,
                   ),
                 );
               }).toList(),

packages/flutter/test/widgets/scrollable_semantics_test.dart

@@ -8,6 +8,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 import 'semantics_tester.dart';
 
@@ -266,6 +267,7 @@ void main() {
     await tester.pumpWidget(Directionality(
       textDirection: TextDirection.ltr,
       child: ListView.builder(
+        dragStartBehavior: DragStartBehavior.down,
         itemExtent: 20.0,
         itemBuilder: (BuildContext context, int index) {
           return Text('entry $index');

packages/flutter/test/widgets/widget_inspector_test.dart

@@ -12,6 +12,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/gestures.dart' show DragStartBehavior;
 
 // Start of block of code where widget creation location line numbers and
 // columns will impact whether tests pass.
@@ -396,6 +397,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
             key: inspectorKey,
             selectButtonBuilder: selectButtonBuilder,
             child: ListView(
+              dragStartBehavior: DragStartBehavior.down,
               children: <Widget>[
                 Container(
                   key: childKey,
@@ -1509,7 +1511,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       _CreationLocation location = knownLocations[id];
       expect(location.file, equals(file));
       // ClockText widget.
-      expect(location.line, equals(49));
+      expect(location.line, equals(50));
       expect(location.column, equals(9));
       expect(count, equals(1));
 
@@ -1518,7 +1520,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       location = knownLocations[id];
       expect(location.file, equals(file));
       // Text widget in _ClockTextState build method.
-      expect(location.line, equals(87));
+      expect(location.line, equals(88));
       expect(location.column, equals(12));
       expect(count, equals(1));
 
@@ -1543,7 +1545,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       location = knownLocations[id];
       expect(location.file, equals(file));
       // ClockText widget.
-      expect(location.line, equals(49));
+      expect(location.line, equals(50));
       expect(location.column, equals(9));
       expect(count, equals(3)); // 3 clock widget instances rebuilt.
 
@@ -1552,7 +1554,7 @@ class TestWidgetInspectorService extends Object with WidgetInspectorService {
       location = knownLocations[id];
       expect(location.file, equals(file));
       // Text widget in _ClockTextState build method.
-      expect(location.line, equals(87));
+      expect(location.line, equals(88));
       expect(location.column, equals(12));
       expect(count, equals(3)); // 3 clock widget instances rebuilt.