Create a CupertinoTab to support parallel navigation trees in iOS (#12130)

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* add a CupertinoTab

* Add default background color

* Add a bunch of examples

* A bunch of tests

* Refactor CupertinoScaffold

* Rename rootTabPageBuilder to tabBuilder

* fix tab transparency padding

* Add default background color

* review notes

* fix test

* review

* Rename CupertinoTab to CupertinoTabView

* remove final ; in sample code for analyzer

packages/flutter/lib/cupertino.dart

@@ -18,6 +18,7 @@ export 'src/cupertino/route.dart';
 export 'src/cupertino/slider.dart';
 export 'src/cupertino/switch.dart';
 export 'src/cupertino/tab_scaffold.dart';
+export 'src/cupertino/tab_view.dart';
 export 'src/cupertino/text_selection.dart';
 export 'src/cupertino/thumb_painter.dart';
 export 'widgets.dart';

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

@@ -29,8 +29,11 @@ const Color _kDefaultTabBarBorderColor = const Color(0x4C000000);
 ///
 /// If the given [backgroundColor]'s opacity is not 1.0 (which is the case by
 /// default), it will produce a blurring effect to the content behind it.
-//
+///
-// TODO(xster): document using with a CupertinoScaffold.
+/// See also:
+///
+///  * [CupertinoTabScaffold] which hosts the [CupertinoTabBar] at the bottom.
+///  * [BottomNavigationBarItem] typical item in a [CupertinoTabBar].
 class CupertinoTabBar extends StatelessWidget implements PreferredSizeWidget {
   /// Creates a tab bar in the iOS style.
   CupertinoTabBar({

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

@@ -50,8 +50,13 @@ const TextStyle _kLargeTitleTextStyle = const TextStyle(
 /// If the given [backgroundColor]'s opacity is not 1.0 (which is the case by
 /// default), it will produce a blurring effect to the content behind it.
 ///
+/// Enabling [largeTitle] will create a scrollable second row showing the title
+/// in a larger font introduced in iOS 11. The [middle] widget must be a text
+/// and the [CupertinoNavigationBar] must be placed in a sliver group in this case.
+///
 /// See also:
 ///
+///  * [CupertinoPageScaffold] page layout helper typically hosting the [CupertinoNavigationBar].
 ///  * [CupertinoSliverNavigationBar] for a nav bar to be placed in a sliver and
 ///    that supports iOS 11 style large titles.
 //

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

@@ -12,7 +12,11 @@ import 'nav_bar.dart';
 ///
 /// The scaffold lays out the navigation bar on top and the content between or
 /// behind the navigation bar.
-// TODO(xster): add an example.
+///
+/// See also:
+///
+///  * [CupertinoPageRoute] a modal page route that typically hosts a [CupertinoPageRoute]
+///    with support for iOS style page transitions.
 class CupertinoPageScaffold extends StatelessWidget {
   const CupertinoPageScaffold({
     Key key,
@@ -37,20 +41,30 @@ class CupertinoPageScaffold extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final List<Widget> stacked = <Widget>[];
+    Widget childWithMediaQuery = child;
+
     double topPadding = 0.0;
     if (navigationBar != null) {
       topPadding += navigationBar.preferredSize.height;
       // If the navigation bar has a preferred size, pad it and the OS status
       // bar as well. Otherwise, let the content extend to the complete top
       // of the page.
-      if (topPadding > 0.0)
+      if (topPadding > 0.0) {
-        topPadding += MediaQuery.of(context).padding.top;
+        final EdgeInsets mediaQueryPadding = MediaQuery.of(context).padding;
+        topPadding += mediaQueryPadding.top;
+        childWithMediaQuery = new MediaQuery(
+          data: MediaQuery.of(context).copyWith(
+            padding: mediaQueryPadding.copyWith(top: 0.0),
+          ),
+          child: child,
+        );
+      }
     }
 
     // The main content being at the bottom is added to the stack first.
     stacked.add(new Padding(
       padding: new EdgeInsets.only(top: topPadding),
-      child: child,
+      child: childWithMediaQuery,
     ));
 
     if (navigationBar != null) {

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

@@ -69,6 +69,8 @@ final DecorationTween _kGradientShadowTween = new DecorationTween(
 ///
 ///  * [MaterialPageRoute] for an adaptive [PageRoute] that uses a platform
 ///    appropriate transition.
+///  * [CupertinoPageScaffold] typical content of a [CupertinoPageRoute] implementing
+///    iOS style layout with navigation bar on top.
 class CupertinoPageRoute<T> extends PageRoute<T> {
   /// Creates a page route for use in an iOS designed app.
   ///

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

@@ -19,8 +19,67 @@ import 'bottom_tab_bar.dart';
 /// tab index. [tabBuilder] must be able to build the same number of
 /// pages as the [tabBar.items.length]. Inactive tabs will be moved [Offstage]
 /// and its animations disabled.
-// TODO(xster): describe navigator handlings.
+///
-// TODO(xster): add an example.
+/// Use [CupertinoTabView] as the content of each tab to support tabs with parallel
+/// navigation state and history.
+///
+/// ## Sample code
+///
+/// A sample code implementing a typical iOS information architecture with tabs.
+///
+/// ```dart
+/// new CupertinoTabScaffold(
+///   tabBar: new CupertinoTabBar(
+///     items: <BottomNavigationBarItem> [
+///       // ...
+///     ],
+///   ),
+///   tabBuilder: (BuildContext context, int index) {
+///     return new CupertinoTabView(
+///       builder: (BuildContext context) {
+///         return new CupertinoPageScaffold(
+///           navigationBar: new CupertinoNavigationBar(
+///             middle: new Text('Page 1 of tab $index'),
+///           ),
+///           child: new Center(
+///             child: new CupertinoButton(
+///               child: const Text('Next page'),
+///               onPressed: () {
+///                 Navigator.of(context).push(
+///                   new CupertinoPageRoute<Null>(
+///                     builder: (BuildContext context) {
+///                       return new CupertinoPageScaffold(
+///                         navigationBar: new CupertinoNavigationBar(
+///                           middle: new Text('Page 2 of tab $index'),
+///                         ),
+///                         child: new Center(
+///                           child: new CupertinoButton(
+///                             child: const Text('Back'),
+///                             onPressed: () { Navigator.of(context).pop(); },
+///                           ),
+///                         ),
+///                       );
+///                     },
+///                   ),
+///                 );
+///               },
+///             ),
+///           ),
+///         );
+///       },
+///     );
+///   },
+/// )
+/// ```
+///
+/// See also:
+///
+///  * [CupertinoTabBar] bottom tab bars inserted in the scaffold.
+///  * [CupertinoTabView] a typical root content of each tap that holds its own
+///    [Navigator] stack.
+///  * [CupertinoPageRoute] a route hosting modal pages with iOS style transitions.
+///  * [CupertinoPageScaffold] typical contents of an iOS modal page implementing
+///    layout with a navigation bar on top.
 class CupertinoTabScaffold extends StatefulWidget {
   const CupertinoTabScaffold({
     Key key,
@@ -48,6 +107,10 @@ class CupertinoTabScaffold extends StatefulWidget {
 
   /// An [IndexedWidgetBuilder] that's called when tabs become active.
   ///
+  /// The widgets built by [IndexedWidgetBuilder] is typically a [CupertinoTabView]
+  /// in order to achieve the parallel hierarchies information architecture seen
+  /// on iOS apps with tab bars.
+  ///
   /// When the tab becomes inactive, its content is still cached in the widget
   /// tree [Offstage] and its animations disabled.
   ///
@@ -138,7 +201,6 @@ class _TabViewState extends State<_TabView> {
       children: new List<Widget>.generate(widget.tabNumber, (int index) {
         final bool active = index == widget.currentTabIndex;
 
-        // TODO(xster): lazily replace empty tabs with Navigators instead.
         if (active || tabs[index] != null)
           tabs[index] = widget.tabBuilder(context, index);
 

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

@@ -0,0 +1,154 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// 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 'package:flutter/widgets.dart';
+
+import 'route.dart';
+
+/// A single tab view with its own [Navigator] state and history.
+///
+/// A typical tab view used as the content of each tab in a [CupertinoTabScaffold]
+/// where multiple tabs with parallel navigation states and history can
+/// co-exist.
+///
+/// [CupertinoTabView] configures the top-level [Navigator] to search for routes
+/// in the following order:
+///
+///  1. For the `/` route, the [builder] property, if non-null, is used.
+///
+///  2. Otherwise, the [routes] table is used, if it has an entry for the route,
+///     including `/` if [builder] is not specified.
+///
+///  3. Otherwise, [onGenerateRoute] is called, if provided. It should return a
+///     non-null value for any _valid_ route not handled by [builder] and [routes].
+///
+///  4. Finally if all else fails [onUnknownRoute] is called.
+///
+/// These navigation properties are not shared with any sibling [CupertinoTabView]
+/// nor any ancestor or descendent [Navigator] instances.
+///
+/// See also:
+///
+///  * [CupertinoTabScaffold] a typical host that supports switching between tabs.
+///  * [CupertinoPageRoute] a typical modal page route pushed onto the [CupertinoTabView]'s
+///    [Navigator].
+class CupertinoTabView extends StatelessWidget {
+  const CupertinoTabView({
+    Key key,
+    this.builder,
+    this.routes,
+    this.onGenerateRoute,
+    this.onUnknownRoute,
+    this.navigatorObservers: const <NavigatorObserver>[],
+  }) : assert(navigatorObservers != null),
+       super(key: key);
+
+  /// The widget builder for the default route of the tab view
+  /// ([Navigator.defaultRouteName], which is `/`).
+  ///
+  /// If a [builder] is specified, then [routes] must not include an entry for `/`,
+  /// as [builder] takes its place.
+  final WidgetBuilder builder;
+
+  /// This tab view's routing table.
+  ///
+  /// When a named route is pushed with [Navigator.pushNamed] inside this tab view,
+  /// the route name is looked up in this map. If the name is present,
+  /// the associated [WidgetBuilder] is used to construct a [CupertinoPageRoute]
+  /// that performs an appropriate transition to the new route.
+  ///
+  /// If the tab view only has one page, then you can specify it using [builder] instead.
+  ///
+  /// If [builder] is specified, then it implies an entry in this table for the
+  /// [Navigator.defaultRouteName] route (`/`), and it is an error to
+  /// redundantly provide such a route in the [routes] table.
+  ///
+  /// If a route is requested that is not specified in this table (or by
+  /// [builder]), then the [onGenerateRoute] callback is called to build the page
+  /// instead.
+  ///
+  /// This routing table is not shared with any routing tables of ancestor or
+  /// descendent [Navigator]s.
+  final Map<String, WidgetBuilder> routes;
+
+  /// The route generator callback used when the tab view is navigated to a named route.
+  ///
+  /// This is used if [routes] does not contain the requested route.
+  final RouteFactory onGenerateRoute;
+
+  /// Called when [onGenerateRoute] also fails to generate a route.
+  ///
+  /// This callback is typically used for error handling. For example, this
+  /// callback might always generate a "not found" page that describes the route
+  /// that wasn't found.
+  ///
+  /// The default implementation pushes a route that displays an ugly error
+  /// message.
+  final RouteFactory onUnknownRoute;
+
+  /// The list of observers for the [Navigator] created in this tab view.
+  ///
+  /// This list of observers is not shared with ancestor or descendent [Navigator]s.
+  final List<NavigatorObserver> navigatorObservers;
+
+  @override
+  Widget build(BuildContext context) {
+    return new Navigator(
+      onGenerateRoute: _onGenerateRoute,
+      onUnknownRoute: _onUnknownRoute,
+      observers: navigatorObservers,
+    );
+  }
+
+  Route<dynamic> _onGenerateRoute(RouteSettings settings) {
+    final String name = settings.name;
+    WidgetBuilder routeBuilder;
+    if (name == Navigator.defaultRouteName && builder != null)
+      routeBuilder = builder;
+    else if (routes != null)
+      routeBuilder = routes[name];
+    if (routeBuilder != null) {
+      return new CupertinoPageRoute<dynamic>(
+        builder: routeBuilder,
+        settings: settings,
+      );
+    }
+    if (onGenerateRoute != null)
+      return onGenerateRoute(settings);
+    return null;
+  }
+
+  Route<dynamic> _onUnknownRoute(RouteSettings settings) {
+    assert(() {
+      if (onUnknownRoute == null) {
+        throw new FlutterError(
+          'Could not find a generator for route $settings in the $runtimeType.\n'
+          'Generators for routes are searched for in the following order:\n'
+          ' 1. For the "/" route, the "builder" property, if non-null, is used.\n'
+          ' 2. Otherwise, the "routes" table is used, if it has an entry for '
+          'the route.\n'
+          ' 3. Otherwise, onGenerateRoute is called. It should return a '
+          'non-null value for any valid route not handled by "builder" and "routes".\n'
+          ' 4. Finally if all else fails onUnknownRoute is called.\n'
+          'Unfortunately, onUnknownRoute was not set.'
+        );
+      }
+      return true;
+    });
+    final Route<dynamic> result = onUnknownRoute(settings);
+    assert(() {
+      if (result == null) {
+        throw new FlutterError(
+          'The onUnknownRoute callback returned null.\n'
+          'When the $runtimeType requested the route $settings from its '
+          'onUnknownRoute callback, the callback returned null. Such callbacks '
+          'must never return null.'
+        );
+      }
+      return true;
+    });
+    return result;
+  }
+}

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

@@ -488,7 +488,6 @@ class _MaterialAppState extends State<MaterialApp> {
     return null;
   }
 
-
   Route<dynamic> _onUnknownRoute(RouteSettings settings) {
     assert(() {
       if (widget.onUnknownRoute == null) {

packages/flutter/lib/src/painting/edge_insets.dart

@@ -559,6 +559,22 @@ class EdgeInsets extends EdgeInsetsGeometry {
 
   @override
   EdgeInsets resolve(TextDirection direction) => this;
+
+  /// Creates a copy of this EdgeInsets but with the given fields replaced
+  /// with the new values.
+  EdgeInsets copyWith({
+    double left,
+    double top,
+    double right,
+    double bottom,
+}) {
+    return new EdgeInsets.only(
+      left: left ?? this.left,
+      top: top ?? this.top,
+      right: right ?? this.right,
+      bottom: bottom ?? this.bottom,
+    );
+  }
 }
 
 /// An immutable set of offsets in each of the four cardinal directions, but

packages/flutter/test/cupertino/scaffold_test.dart

@@ -77,4 +77,121 @@ void main() {
 
     expect(tester.getSize(find.byWidget(page1Center)).height, 600.0 - 44.0 - 50.0);
   });
+
+  testWidgets('iOS independent tab navigation', (WidgetTester tester) async {
+    // A full on iOS information architecture app with 2 tabs, and 2 pages
+    // in each with independent navigation states.
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabScaffold(
+                tabBar: new CupertinoTabBar(
+                  items: <BottomNavigationBarItem>[
+                    const BottomNavigationBarItem(
+                      icon: const ImageIcon(const TestImageProvider(24, 24)),
+                      title: const Text('Tab 1'),
+                    ),
+                    const BottomNavigationBarItem(
+                      icon: const ImageIcon(const TestImageProvider(24, 24)),
+                      title: const Text('Tab 2'),
+                    ),
+                  ],
+                ),
+                tabBuilder: (BuildContext context, int index) {
+                  // For 1-indexed readability.
+                  ++index;
+                  return new CupertinoTabView(
+                    builder: (BuildContext context) {
+                      return new CupertinoPageScaffold(
+                        navigationBar: new CupertinoNavigationBar(
+                          middle: new Text('Page 1 of tab $index'),
+                        ),
+                        child: new Center(
+                          child: new CupertinoButton(
+                            child: const Text('Next'),
+                            onPressed: () {
+                              Navigator.of(context).push(
+                                new CupertinoPageRoute<Null>(
+                                  builder: (BuildContext context) {
+                                    return new CupertinoPageScaffold(
+                                      navigationBar: new CupertinoNavigationBar(
+                                        middle: new Text('Page 2 of tab $index'),
+                                      ),
+                                      child: new Center(
+                                        child: new CupertinoButton(
+                                          child: const Text('Back'),
+                                          onPressed: (){
+                                            Navigator.of(context).pop();
+                                          },
+                                        ),
+                                      ),
+                                    );
+                                  },
+                                ),
+                              );
+                            },
+                          ),
+                        ),
+                      );
+                    },
+                  );
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(find.text('Page 1 of tab 1'), findsOneWidget);
+    expect(find.text('Page 1 of tab 2'), findsNothing); // Lazy building so not built yet.
+
+    await tester.tap(find.text('Tab 2'));
+    await tester.pump();
+
+    expect(find.text('Page 1 of tab 1'), findsNothing); // It's offstage now.
+    expect(find.text('Page 1 of tab 1', skipOffstage: false), findsOneWidget);
+    expect(find.text('Page 1 of tab 2'), findsOneWidget);
+
+    // Navigate in tab 2.
+    await tester.tap(find.text('Next'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+
+    expect(find.text('Page 2 of tab 2'), isOnstage);
+    expect(find.text('Page 1 of tab 1', skipOffstage: false), isOffstage);
+
+    await tester.tap(find.text('Tab 1'));
+    await tester.pump();
+
+    // Independent navigation stacks.
+    expect(find.text('Page 1 of tab 1'), isOnstage);
+    expect(find.text('Page 2 of tab 2', skipOffstage: false), isOffstage);
+
+    // Navigate in tab 1.
+    await tester.tap(find.text('Next'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+
+    expect(find.text('Page 2 of tab 1'), isOnstage);
+    expect(find.text('Page 2 of tab 2', skipOffstage: false), isOffstage);
+
+    await tester.tap(find.text('Tab 2'));
+    await tester.pump();
+
+    expect(find.text('Page 2 of tab 2'), isOnstage);
+    expect(find.text('Page 2 of tab 1', skipOffstage: false), isOffstage);
+
+    // Pop in tab 2
+    await tester.tap(find.text('Back'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+
+    expect(find.text('Page 1 of tab 2'), isOnstage);
+    expect(find.text('Page 2 of tab 1', skipOffstage: false), isOffstage);
+  });
 }

packages/flutter/test/cupertino/tab_test.dart

@@ -0,0 +1,137 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// 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_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Use home', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabView(
+                builder: (BuildContext context) => const Text('home'),
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(find.text('home'), findsOneWidget);
+  });
+
+  testWidgets('Use routes', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabView(
+                routes: <String, WidgetBuilder>{
+                  '/': (BuildContext context) => const Text('first route'),
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(find.text('first route'), findsOneWidget);
+  });
+
+  testWidgets('Use home and named routes', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabView(
+                builder: (BuildContext context) {
+                  return new CupertinoButton(
+                    child: const Text('go to second page'),
+                    onPressed: () {
+                      Navigator.of(context).pushNamed('/2');
+                    },
+                  );
+                },
+                routes: <String, WidgetBuilder>{
+                  '/2': (BuildContext context) => const Text('second named route'),
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(find.text('go to second page'), findsOneWidget);
+    await tester.tap(find.text('go to second page'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 300));
+    expect(find.text('second named route'), findsOneWidget);
+  });
+
+  testWidgets('Use onGenerateRoute', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabView(
+                onGenerateRoute: (RouteSettings settings) {
+                  if (settings.name == Navigator.defaultRouteName) {
+                    return new CupertinoPageRoute<Null>(
+                      settings: settings,
+                      builder: (BuildContext context) {
+                        return const Text('generated home');
+                      }
+                    );
+                  }
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(find.text('generated home'), findsOneWidget);
+  });
+
+  testWidgets('Use onUnknownRoute', (WidgetTester tester) async {
+    String unknownForRouteCalled;
+    await tester.pumpWidget(
+      new WidgetsApp(
+        color: const Color(0xFFFFFFFF),
+        onGenerateRoute: (RouteSettings settings) {
+          return new CupertinoPageRoute<Null>(
+            settings: settings,
+            builder: (BuildContext context) {
+              return new CupertinoTabView(
+                onUnknownRoute: (RouteSettings settings) {
+                  unknownForRouteCalled = settings.name;
+                },
+              );
+            },
+          );
+        },
+      ),
+    );
+
+    expect(tester.takeException(), isFlutterError);
+    expect(unknownForRouteCalled, '/');
+  });
+}

packages/flutter/test/painting/edge_insets_test.dart

@@ -94,6 +94,12 @@ void main() {
     expect(const EdgeInsetsDirectional.only(top: 1.0).add(const EdgeInsets.only(top: 2.0)), const EdgeInsets.only(top: 3.0));
   });
 
+  test('EdgeInsets copyWith', () {
+    final EdgeInsets sourceEdgeInsets = const EdgeInsets.only(left: 1.0, top: 2.0, bottom: 3.0, right: 4.0);
+    final EdgeInsets copy = sourceEdgeInsets.copyWith(left: 5.0, top: 6.0);
+    expect(copy, const EdgeInsets.only(left: 5.0, top: 6.0, bottom: 3.0, right: 4.0));
+  });
+
   test('EdgeInsetsGeometry.lerp(...)', () {
     expect(EdgeInsetsGeometry.lerp(const EdgeInsetsDirectional.only(end: 10.0), null, 0.5), const EdgeInsetsDirectional.only(end: 5.0));
     expect(EdgeInsetsGeometry.lerp(const EdgeInsetsDirectional.only(start: 10.0), null, 0.5), const EdgeInsetsDirectional.only(start: 5.0));