Added support for a pinned floating SliverAppBar (#8345)

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

@@ -96,6 +96,29 @@ class _ToolbarLayout extends MultiChildLayoutDelegate {
   bool shouldRelayout(_ToolbarLayout oldDelegate) => centerTitle != oldDelegate.centerTitle;
 }
 
+// Bottom justify the kToolbarHeight child which may overflow the top.
+class _ToolbarContainerLayout extends SingleChildLayoutDelegate {
+  const _ToolbarContainerLayout();
+
+  @override
+  BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
+    return constraints.tighten(height: kToolbarHeight);
+  }
+
+  @override
+  Size getSize(BoxConstraints constraints) {
+    return new Size(constraints.maxWidth, kToolbarHeight);
+  }
+
+  @override
+  Offset getPositionForChild(Size size, Size childSize) {
+    return new Offset(0.0, size.height - childSize.height);
+  }
+
+  @override
+  bool shouldRelayout(_ToolbarContainerLayout oldDelegate) => false;
+}
+
 // TODO(eseidel) Toolbar needs to change size based on orientation:
 // http://material.google.com/layout/structure.html#structure-app-bar
 // Mobile Landscape: 48dp
@@ -425,8 +448,11 @@ class _AppBarState extends State<AppBar> {
       ),
     );
 
-    Widget appBar = new SizedBox(
+    // If the toolbar is allocated less than kToolbarHeight make it
-      height: kToolbarHeight,
+    // appear to scroll upwards within its shrinking container.
+    Widget appBar = new ClipRect(
+      child: new CustomSingleChildLayout(
+        delegate: const _ToolbarContainerLayout(),
         child: new IconTheme.merge(
           context: context,
           data: appBarIconTheme,
@@ -435,14 +461,19 @@ class _AppBarState extends State<AppBar> {
             child: toolbar,
           ),
         ),
+      ),
     );
 
-
     if (config.bottom != null) {
       appBar = new Column(
         mainAxisAlignment: MainAxisAlignment.spaceBetween,
         children: <Widget>[
-          appBar,
+          new Flexible(
+            child: new ConstrainedBox(
+              constraints: new BoxConstraints(maxHeight: kToolbarHeight),
+              child: appBar,
+            ),
+          ),
           config.bottomOpacity == 1.0 ? config.bottom : new Opacity(
             opacity: const Interval(0.25, 1.0, curve: Curves.fastOutSlowIn).transform(config.bottomOpacity),
             child: config.bottom,
@@ -494,7 +525,9 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
     @required this.primary,
     @required this.centerTitle,
     @required this.expandedHeight,
+    @required this.collapsedHeight,
     @required this.topPadding,
+    @required this.floating,
     @required this.pinned,
   }) : bottom = bottom,
       _bottomHeight = bottom?.bottomHeight ?? 0.0 {
@@ -514,21 +547,24 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
   final bool primary;
   final bool centerTitle;
   final double expandedHeight;
+  final double collapsedHeight;
   final double topPadding;
+  final bool floating;
   final bool pinned;
 
   final double _bottomHeight;
 
   @override
-  double get minExtent => topPadding + kToolbarHeight + _bottomHeight;
+  double get minExtent => collapsedHeight ?? (topPadding + kToolbarHeight + _bottomHeight);
 
   @override
-  double get maxExtent => math.max(topPadding + (expandedHeight ?? kToolbarHeight), minExtent);
+  double get maxExtent => math.max(topPadding + (expandedHeight ?? kToolbarHeight + _bottomHeight), minExtent);
 
   @override
   Widget build(BuildContext context, double shrinkOffset, bool overlapsContent) {
-    double visibleMainHeight = maxExtent - shrinkOffset - topPadding;
+    final double visibleMainHeight = maxExtent - shrinkOffset - topPadding;
-    double toolbarOpacity = pinned ? 1.0 : ((visibleMainHeight - _bottomHeight) / kToolbarHeight).clamp(0.0, 1.0);
+    final double toolbarOpacity = pinned && !floating ? 1.0
+      : ((visibleMainHeight - _bottomHeight) / kToolbarHeight).clamp(0.0, 1.0);
     return FlexibleSpaceBar.createSettings(
       minExtent: minExtent,
       maxExtent: maxExtent,
@@ -569,7 +605,9 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
         || primary != oldDelegate.primary
         || centerTitle != oldDelegate.centerTitle
         || expandedHeight != oldDelegate.expandedHeight
-        || topPadding != oldDelegate.topPadding;
+        || topPadding != oldDelegate.topPadding
+        || pinned != oldDelegate.pinned
+        || floating != oldDelegate.floating;
   }
 
   @override
@@ -630,7 +668,7 @@ class SliverAppBar extends StatelessWidget {
     assert(primary != null);
     assert(floating != null);
     assert(pinned != null);
-    assert(!floating || !pinned);
+    assert(pinned && floating ? bottom != null : true);
   }
 
   /// A widget to display before the [title].
@@ -763,6 +801,10 @@ class SliverAppBar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    final double topPadding = primary ? MediaQuery.of(context).padding.top : 0.0;
+    final double collapsedHeight = (pinned && floating && bottom != null)
+      ? bottom.bottomHeight + topPadding : null;
+
     return new SliverPersistentHeader(
       floating: floating,
       pinned: pinned,
@@ -780,7 +822,9 @@ class SliverAppBar extends StatelessWidget {
         primary: primary,
         centerTitle: centerTitle,
         expandedHeight: expandedHeight,
-        topPadding: primary ? MediaQuery.of(context).padding.top : 0.0,
+        collapsedHeight: collapsedHeight,
+        topPadding: topPadding,
+        floating: floating,
         pinned: pinned,
       ),
     );

packages/flutter/lib/src/rendering/shifted_box.dart

@@ -700,6 +700,10 @@ class RenderFractionallySizedOverflowBox extends RenderAligningShiftedBox {
 
 /// A delegate for computing the layout of a render object with a single child.
 abstract class SingleChildLayoutDelegate {
+  /// Abstract const constructor. This constructor enables subclasses to provide
+  /// const constructors so that they can be used in const expressions.
+  const SingleChildLayoutDelegate();
+
   // TODO(abarth): This class should take a Listenable to drive relayout.
 
   /// The size of this object given the incoming constraints.

packages/flutter/lib/src/rendering/sliver_persistent_header.dart

@@ -265,6 +265,23 @@ abstract class RenderSliverFloatingPersistentHeader extends RenderSliverPersiste
   // direction. Negative if we're scrolled off the top.
   double _childPosition;
 
+  // Update [geometry] and return the new value for [childMainAxisPosition].
+  @protected
+  double updateGeometry() {
+    final double maxExtent = this.maxExtent;
+    final double paintExtent = maxExtent - _effectiveScrollOffset;
+    final double layoutExtent = maxExtent - constraints.scrollOffset;
+    geometry = new SliverGeometry(
+      scrollExtent: maxExtent,
+      paintExtent: paintExtent.clamp(0.0, constraints.remainingPaintExtent),
+      layoutExtent: layoutExtent.clamp(0.0, constraints.remainingPaintExtent),
+      maxPaintExtent: maxExtent,
+      hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.
+    );
+    return math.min(0.0, paintExtent - childExtent);
+  }
+
+
   @override
   void performLayout() {
     final double maxExtent = this.maxExtent;
@@ -285,16 +302,7 @@ abstract class RenderSliverFloatingPersistentHeader extends RenderSliverPersiste
       _effectiveScrollOffset = constraints.scrollOffset;
     }
     layoutChild(_effectiveScrollOffset, maxExtent, overlapsContent: _effectiveScrollOffset < constraints.scrollOffset);
-    final double paintExtent = maxExtent - _effectiveScrollOffset;
+    _childPosition = updateGeometry();
-    final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
-    geometry = new SliverGeometry(
-      scrollExtent: maxExtent,
-      paintExtent: paintExtent.clamp(0.0, constraints.remainingPaintExtent),
-      layoutExtent: layoutExtent,
-      maxPaintExtent: maxExtent,
-      hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.
-    );
-    _childPosition = math.min(0.0, paintExtent - childExtent);
     _lastActualScrollOffset = constraints.scrollOffset;
   }
 
@@ -310,3 +318,25 @@ abstract class RenderSliverFloatingPersistentHeader extends RenderSliverPersiste
     description.add('effective scroll offset: ${_effectiveScrollOffset?.toStringAsFixed(1)}');
   }
 }
+
+abstract class RenderSliverFloatingPinnedPersistentHeader extends RenderSliverFloatingPersistentHeader {
+  RenderSliverFloatingPinnedPersistentHeader({
+    RenderBox child,
+  }) : super(child: child);
+
+  @override
+  double updateGeometry() {
+    final double minExtent = this.maxExtent;
+    final double maxExtent = this.maxExtent;
+    final double paintExtent = (maxExtent - _effectiveScrollOffset);
+    final double layoutExtent = (maxExtent - constraints.scrollOffset);
+    geometry = new SliverGeometry(
+      scrollExtent: maxExtent,
+      paintExtent: paintExtent.clamp(minExtent, constraints.remainingPaintExtent),
+      layoutExtent: layoutExtent.clamp(0.0, constraints.remainingPaintExtent - minExtent),
+      maxPaintExtent: maxExtent,
+      hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.
+    );
+    return 0.0;
+  }
+}

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

@@ -31,7 +31,6 @@ class SliverPersistentHeader extends StatelessWidget {
     assert(delegate != null);
     assert(pinned != null);
     assert(floating != null);
-    assert(!pinned || !floating);
   }
 
   final SliverPersistentHeaderDelegate delegate;
@@ -42,6 +41,8 @@ class SliverPersistentHeader extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    if (floating && pinned)
+      return new _SliverFloatingPinnedPersistentHeader(delegate: delegate);
     if (pinned)
       return new _SliverPinnedPersistentHeader(delegate: delegate);
     if (floating)
@@ -227,6 +228,23 @@ class _SliverFloatingPersistentHeader extends _SliverPersistentHeaderRenderObjec
   }
 }
 
+// This class exists to work around https://github.com/dart-lang/sdk/issues/15101
+abstract class _RenderSliverFloatingPinnedPersistentHeader extends RenderSliverFloatingPinnedPersistentHeader { }
+
+class _RenderSliverFloatingPinnedPersistentHeaderForWidgets extends _RenderSliverFloatingPinnedPersistentHeader with _RenderSliverPersistentHeaderForWidgetsMixin { }
+
+class _SliverFloatingPinnedPersistentHeader extends _SliverPersistentHeaderRenderObjectWidget {
+  _SliverFloatingPinnedPersistentHeader({
+    Key key,
+    @required SliverPersistentHeaderDelegate delegate,
+  }) : super(key: key, delegate: delegate);
+
+  @override
+  _RenderSliverPersistentHeaderForWidgetsMixin createRenderObject(BuildContext context) {
+    return new _RenderSliverFloatingPinnedPersistentHeaderForWidgets();
+  }
+}
+
 // This class exists to work around https://github.com/dart-lang/sdk/issues/15101
 abstract class _RenderSliverFloatingPersistentHeader extends RenderSliverFloatingPersistentHeader { }
 

packages/flutter/test/material/app_bar_test.dart

@@ -4,8 +4,55 @@
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/rendering.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+Widget buildSliverAppBarApp({ bool floating, bool pinned, double expandedHeight }) {
+  return new Scaffold(
+    body: new CustomScrollView(
+      primary: true,
+      slivers: <Widget>[
+        new SliverAppBar(
+          title: new Text('AppBar Title'),
+          floating: floating,
+          pinned: pinned,
+          expandedHeight: expandedHeight,
+          bottom: new TabBar(
+            tabs: <String>['A','B','C'].map((String t) => new Tab(text: 'TAB $t')).toList(),
+          ),
+        ),
+        new SliverToBoxAdapter(
+          child: new Container(
+            height: 1200.0,
+            decoration: new BoxDecoration(backgroundColor: Colors.orange[400]),
+          ),
+        ),
+      ],
+    ),
+  );
+}
+
+ScrollController primaryScrollController(WidgetTester tester) {
+  return PrimaryScrollController.of(tester.element(find.byType(CustomScrollView)));
+}
+
+bool appBarIsVisible(WidgetTester tester) {
+  final RenderSliver sliver = tester.element(find.byType(SliverAppBar)).findRenderObject();
+  return sliver.geometry.visible;
+}
+
+double appBarHeight(WidgetTester tester) {
+  final Element element = tester.element(find.byType(AppBar));
+  final RenderBox box = element.findRenderObject();
+  return box.size.height;
+}
+
+double tabBarHeight(WidgetTester tester) {
+  final Element element = tester.element(find.byType(TabBar));
+  final RenderBox box = element.findRenderObject();
+  return box.size.height;
+}
+
 void main() {
   testWidgets('AppBar centers title on iOS', (WidgetTester tester) async {
     await tester.pumpWidget(
@@ -305,4 +352,105 @@ void main() {
     expect(tester.getSize(shareButton), new Size(48.0, 56.0));
   });
 
+  testWidgets('SliverAppBar default configuration', (WidgetTester tester) async {
+    await tester.pumpWidget(buildSliverAppBarApp(
+      floating: false,
+      pinned: false,
+      expandedHeight: null,
+    ));
+
+    ScrollController controller = primaryScrollController(tester);
+    expect(controller.offset, 0.0);
+    expect(appBarIsVisible(tester), true);
+
+    final double initialAppBarHeight = appBarHeight(tester);
+    final double initialTabBarHeight = tabBarHeight(tester);
+
+    // Scroll the not-pinned appbar partially out of view
+    controller.jumpTo(50.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), initialAppBarHeight);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+
+    // Scroll the not-pinned appbar out of view
+    controller.jumpTo(600.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), false);
+    expect(appBarHeight(tester), initialAppBarHeight);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+
+    // Scroll the not-pinned appbar back into view
+    controller.jumpTo(0.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), initialAppBarHeight);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+  });
+
+  testWidgets('SliverAppBar expandedHeight, pinned', (WidgetTester tester) async {
+
+    await tester.pumpWidget(buildSliverAppBarApp(
+      floating: false,
+      pinned: true,
+      expandedHeight: 128.0,
+    ));
+
+    ScrollController controller = primaryScrollController(tester);
+    expect(controller.offset, 0.0);
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), 128.0);
+
+    final double initialAppBarHeight = 128.0;
+    final double initialTabBarHeight = tabBarHeight(tester);
+
+    // Scroll the not-pinned appbar, collapsing the expanded height. At this
+    // point both the toolbar and the tabbar are visible.
+    controller.jumpTo(600.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+    expect(appBarHeight(tester), lessThan(initialAppBarHeight));
+    expect(appBarHeight(tester), greaterThan(initialTabBarHeight));
+
+    // Scroll the not-pinned appbar back into view
+    controller.jumpTo(0.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), initialAppBarHeight);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+  });
+
+  testWidgets('SliverAppBar expandedHeight, pinned and floating', (WidgetTester tester) async {
+
+    await tester.pumpWidget(buildSliverAppBarApp(
+      floating: true,
+      pinned: true,
+      expandedHeight: 128.0,
+    ));
+
+    ScrollController controller = primaryScrollController(tester);
+    expect(controller.offset, 0.0);
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), 128.0);
+
+    final double initialAppBarHeight = 128.0;
+    final double initialTabBarHeight = tabBarHeight(tester);
+
+    // Scroll the not-pinned appbar, collapsing the expanded height. At this
+    // point only the tabBar is visible.
+    controller.jumpTo(600.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+    expect(appBarHeight(tester), lessThan(initialAppBarHeight));
+    expect(appBarHeight(tester), initialTabBarHeight);
+
+    // Scroll the not-pinned appbar back into view
+    controller.jumpTo(0.0);
+    await tester.pump();
+    expect(appBarIsVisible(tester), true);
+    expect(appBarHeight(tester), initialAppBarHeight);
+    expect(tabBarHeight(tester), initialTabBarHeight);
+  });
 }