CupertinoPageRoute cleanup (#11473)

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

@@ -72,19 +72,28 @@ class MaterialPageRoute<T> extends PageRoute<T> {
   /// Builds the primary contents of the route.
   final WidgetBuilder builder;
 
+  @override
+  final bool maintainState;
+
   /// A delegate PageRoute to which iOS themed page operations are delegated to.
   /// It's lazily created on first use.
-  CupertinoPageRoute<T> _internalCupertinoPageRoute;
   CupertinoPageRoute<T> get _cupertinoPageRoute {
+    assert(_useCupertinoTransitions);
     _internalCupertinoPageRoute ??= new CupertinoPageRoute<T>(
       builder: builder, // Not used.
       fullscreenDialog: fullscreenDialog,
+      hostRoute: this,
     );
     return _internalCupertinoPageRoute;
   }
+  CupertinoPageRoute<T> _internalCupertinoPageRoute;
 
-  @override
-  final bool maintainState;
+  /// Whether we should currently be using Cupertino transitions. This is true
+  /// if the theme says we're on iOS, or if we're in an active gesture.
+  bool get _useCupertinoTransitions {
+    return _internalCupertinoPageRoute?.popGestureInProgress == true
+        || Theme.of(navigator.context).platform == TargetPlatform.iOS;
+  }
 
   @override
   Duration get transitionDuration => const Duration(milliseconds: 300);
@@ -93,8 +102,8 @@ class MaterialPageRoute<T> extends PageRoute<T> {
   Color get barrierColor => null;
 
   @override
-  bool canTransitionFrom(TransitionRoute<dynamic> nextRoute) {
-    return nextRoute is MaterialPageRoute<dynamic> || nextRoute is CupertinoPageRoute<dynamic>;
+  bool canTransitionFrom(TransitionRoute<dynamic> previousRoute) {
+    return (previousRoute is MaterialPageRoute || previousRoute is CupertinoPageRoute);
   }
 
   @override
@@ -110,23 +119,6 @@ class MaterialPageRoute<T> extends PageRoute<T> {
     super.dispose();
   }
 
-  /// Support for dismissing this route with a horizontal swipe is enabled
-  /// for [TargetPlatform.iOS]. If attempts to dismiss this route might be
-  /// vetoed because a [WillPopCallback] was defined for the route then the
-  /// platform-specific back gesture is disabled.
-  ///
-  /// See also:
-  ///
-  ///  * [CupertinoPageRoute] that backs the gesture for iOS.
-  ///  * [hasScopedWillPopCallback], which is true if a `willPop` callback
-  ///    is defined for this route.
-  @override
-  NavigationGestureController startPopGesture() {
-    return Theme.of(navigator.context).platform == TargetPlatform.iOS
-        ? _cupertinoPageRoute.startPopGestureForRoute(this)
-        : null;
-  }
-
   @override
   Widget buildPage(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation) {
     final Widget result = builder(context);
@@ -144,12 +136,12 @@ class MaterialPageRoute<T> extends PageRoute<T> {
 
   @override
   Widget buildTransitions(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation, Widget child) {
-    if (Theme.of(context).platform == TargetPlatform.iOS) {
+    if (_useCupertinoTransitions) {
       return _cupertinoPageRoute.buildTransitions(context, animation, secondaryAnimation, child);
     } else {
       return new _MountainViewPageTransition(
         routeAnimation: animation,
-        child: child
+        child: child,
       );
     }
   }

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

@@ -23,8 +23,6 @@ const double _kFloatingActionButtonMargin = 16.0; // TODO(hmuller): should be de
 const Duration _kFloatingActionButtonSegue = const Duration(milliseconds: 200);
 final Tween<double> _kFloatingActionButtonTurnTween = new Tween<double>(begin: -0.125, end: 0.0);
 
-const double _kBackGestureWidth = 20.0;
-
 enum _ScaffoldSlot {
   body,
   appBar,
@@ -717,40 +715,6 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
     }
   }
 
-  final GlobalKey _backGestureKey = new GlobalKey();
-  NavigationGestureController _backGestureController;
-
-  bool _shouldHandleBackGesture() {
-    assert(mounted);
-    return Theme.of(context).platform == TargetPlatform.iOS && Navigator.canPop(context);
-  }
-
-  void _handleDragStart(DragStartDetails details) {
-    assert(mounted);
-    _backGestureController = Navigator.of(context).startPopGesture();
-  }
-
-  void _handleDragUpdate(DragUpdateDetails details) {
-    assert(mounted);
-    _backGestureController?.dragUpdate(details.primaryDelta / context.size.width);
-  }
-
-  void _handleDragEnd(DragEndDetails details) {
-    assert(mounted);
-    final bool willPop = _backGestureController?.dragEnd(details.velocity.pixelsPerSecond.dx / context.size.width) ?? false;
-    if (willPop)
-      _currentBottomSheet?.close();
-    _backGestureController = null;
-  }
-
-  void _handleDragCancel() {
-    assert(mounted);
-    final bool willPop = _backGestureController?.dragEnd(0.0) ?? false;
-    if (willPop)
-      _currentBottomSheet?.close();
-    _backGestureController = null;
-  }
-
 
   // INTERNALS
 
@@ -887,25 +851,6 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin {
           child: widget.drawer,
         )
       ));
-    } else if (_shouldHandleBackGesture()) {
-      assert(!hasDrawer);
-      // Add a gesture for navigating back.
-      children.add(new LayoutId(
-        id: _ScaffoldSlot.drawer,
-        child: new Align(
-          alignment: FractionalOffset.centerLeft,
-          child: new GestureDetector(
-            key: _backGestureKey,
-            onHorizontalDragStart: _handleDragStart,
-            onHorizontalDragUpdate: _handleDragUpdate,
-            onHorizontalDragEnd: _handleDragEnd,
-            onHorizontalDragCancel: _handleDragCancel,
-            behavior: HitTestBehavior.translucent,
-            excludeFromSemantics: true,
-            child: new Container(width: _kBackGestureWidth)
-          )
-        )
-      ));
     }
 
     return new _ScaffoldScope(

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

@@ -3113,6 +3113,8 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
           'resulting object.\n'
           'The size getter was called for the following element:\n'
           '  $this\n'
+          'The associated render sliver was:\n'
+          '  ${renderObject.toStringShallow("\n  ")}'
         );
       }
       if (renderObject is! RenderBox) {
@@ -3124,10 +3126,12 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
           'and extracting its size manually.\n'
           'The size getter was called for the following element:\n'
           '  $this\n'
+          'The associated render object was:\n'
+          '  ${renderObject.toStringShallow("\n  ")}'
         );
       }
       final RenderBox box = renderObject;
-      if (!box.hasSize || box.debugNeedsLayout) {
+      if (!box.hasSize) {
         throw new FlutterError(
           'Cannot get size from a render object that has not been through layout.\n'
           'The size of this render object has not yet been determined because '
@@ -3137,6 +3141,24 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
           'the size and position of the render objects during layout.\n'
           'The size getter was called for the following element:\n'
           '  $this\n'
+          'The render object from which the size was to be obtained was:\n'
+          '  ${box.toStringShallow("\n  ")}'
+        );
+      }
+      if (box.debugNeedsLayout) {
+        throw new FlutterError(
+          'Cannot get size from a render object that has been marked dirty for layout.\n'
+          'The size of this render object is ambiguous because this render object has '
+          'been modified since it was last laid out, which typically means that the size '
+          'getter was called too early in the pipeline (e.g., during the build phase) '
+          'before the framework has determined the size and position of the render '
+          'objects during layout.\n'
+          'The size getter was called for the following element:\n'
+          '  $this\n'
+          'The render object from which the size was to be obtained was:\n'
+          '  ${box.toStringShallow("\n  ")}\n'
+          'Consider using debugPrintMarkNeedsLayoutStacks to determine why the render '
+          'object in question is dirty, if you did not expect this.'
         );
       }
       return true;

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

@@ -178,29 +178,9 @@ abstract class Route<T> {
   @mustCallSuper
   @protected
   void dispose() {
-    assert(() {
-      if (navigator == null) {
-        throw new FlutterError(
-          '$runtimeType.dipose() called more than once.\n'
-          'A given route cannot be disposed more than once.'
-        );
-      }
-      return true;
-    });
     _navigator = null;
   }
 
-  /// If the route's transition can be popped via a user gesture (e.g. the iOS
-  /// back gesture), this should return a controller object that can be used to
-  /// control the transition animation's progress. Otherwise, it should return
-  /// null.
-  ///
-  /// If attempts to dismiss this route might be vetoed, for example because
-  /// a [WillPopCallback] was defined for the route, then it may make sense
-  /// to disable the pop gesture. For example, the iOS back gesture is disabled
-  /// when [ModalRoute.hasScopedWillPopCallback] is true.
-  NavigationGestureController startPopGesture() => null;
-
   /// Whether this route is the top-most route on the navigator.
   ///
   /// If this is true, then [isActive] is also true.
@@ -288,54 +268,16 @@ class NavigatorObserver {
   /// The [Navigator] removed `route`.
   void didRemove(Route<dynamic> route, Route<dynamic> previousRoute) { }
 
-  /// The [Navigator] is being controlled by a user gesture.
+  /// The [Navigator]'s routes are being moved by a user gesture.
   ///
-  /// Used for the iOS back gesture.
+  /// For example, this is called when an iOS back gesture starts, and is used
+  /// to disabled hero animations during such interactions.
   void didStartUserGesture() { }
 
   /// User gesture is no longer controlling the [Navigator].
-  void didStopUserGesture() { }
-}
-
-/// Interface describing an object returned by the [Route.startPopGesture]
-/// method, allowing the route's transition animations to be controlled by a
-/// drag or other user gesture.
-abstract class NavigationGestureController {
-  /// Configures the NavigationGestureController and tells the given [Navigator] that
-  /// a gesture has started.
-  NavigationGestureController(this._navigator)
-    : assert(_navigator != null) {
-    // Disable Hero transitions until the gesture is complete.
-    _navigator.didStartUserGesture();
-  }
-
-  /// The navigator that this object is controlling.
-  @protected
-  NavigatorState get navigator => _navigator;
-  NavigatorState _navigator;
-
-  /// Release the resources used by this object. The object is no longer usable
-  /// after this method is called.
-  ///
-  /// Must be called when the gesture is done.
-  ///
-  /// Calling this method notifies the navigator that the gesture has completed.
-  @mustCallSuper
-  void dispose() {
-    _navigator.didStopUserGesture();
-    _navigator = null;
-  }
-
-  /// The drag gesture has changed by [fractionalDelta]. The total range of the
-  /// drag should be 0.0 to 1.0.
-  void dragUpdate(double fractionalDelta);
-
-  /// The drag gesture has ended with a horizontal motion of
-  /// [fractionalVelocity] as a fraction of screen width per second.
   ///
-  /// Returns true if the gesture will complete (i.e. a back gesture will
-  /// result in a pop).
-  bool dragEnd(double fractionalVelocity);
+  /// Paired with an earlier call to [didStartUserGesture].
+  void didStopUserGesture() { }
 }
 
 /// Signature for the [Navigator.popUntil] predicate argument.
@@ -1326,34 +1268,36 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     return _history.length > 1 || _history[0].willHandlePopInternally;
   }
 
-  /// Starts a gesture that results in popping the navigator.
-  NavigationGestureController startPopGesture() {
-    if (canPop())
-      return _history.last.startPopGesture();
-    return null;
-  }
-
-  /// Whether a gesture controlled by a [NavigationGestureController] is currently in progress.
-  bool get userGestureInProgress => _userGestureInProgress;
-  // TODO(mpcomplete): remove this bool when we fix
-  // https://github.com/flutter/flutter/issues/5577
-  bool _userGestureInProgress = false;
+  /// Whether a route is currently being manipulated by the user, e.g.
+  /// as during an iOS back gesture.
+  bool get userGestureInProgress => _userGesturesInProgress > 0;
+  int _userGesturesInProgress = 0;
 
   /// The navigator is being controlled by a user gesture.
   ///
-  /// Used for the iOS back gesture.
+  /// For example, called when the user beings an iOS back gesture.
+  ///
+  /// When the gesture finishes, call [didStopUserGesture].
   void didStartUserGesture() {
-    _userGestureInProgress = true;
+    _userGesturesInProgress += 1;
+    if (_userGesturesInProgress == 1) {
       for (NavigatorObserver observer in widget.observers)
         observer.didStartUserGesture();
     }
+  }
 
-  /// A user gesture is no longer controlling the navigator.
+  /// A user gesture completed.
+  ///
+  /// Notifies the navigator that a gesture regarding which the navigator was
+  /// previously notified with [didStartUserGesture] has completed.
   void didStopUserGesture() {
-    _userGestureInProgress = false;
+    assert(_userGesturesInProgress > 0);
+    _userGesturesInProgress -= 1;
+    if (_userGesturesInProgress == 0) {
       for (NavigatorObserver observer in widget.observers)
         observer.didStopUserGesture();
     }
+  }
 
   final Set<int> _activePointers = new Set<int>();
 

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

@@ -32,10 +32,10 @@ abstract class PageRoute<T> extends ModalRoute<T> {
   bool get barrierDismissible => false;
 
   @override
-  bool canTransitionTo(TransitionRoute<dynamic> nextRoute) => nextRoute is PageRoute<dynamic>;
+  bool canTransitionTo(TransitionRoute<dynamic> nextRoute) => nextRoute is PageRoute;
 
   @override
-  bool canTransitionFrom(TransitionRoute<dynamic> nextRoute) => nextRoute is PageRoute<dynamic>;
+  bool canTransitionFrom(TransitionRoute<dynamic> previousRoute) => previousRoute is PageRoute;
 
   @override
   AnimationController createAnimationController() {

packages/flutter/test/material/page_test.dart

@@ -272,6 +272,73 @@ void main() {
     expect(tester.getTopLeft(find.text('Page 2')), const Offset(100.0, 0.0));
   });
 
+  testWidgets('back gesture while OS changes', (WidgetTester tester) async {
+    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
+      '/': (BuildContext context) => new Material(
+        child: new FlatButton(
+          child: new Text('PUSH'),
+          onPressed: () { Navigator.of(context).pushNamed('/b'); },
+        ),
+      ),
+      '/b': (BuildContext context) => new Container(child: new Text('HELLO')),
+    };
+    await tester.pumpWidget(
+      new MaterialApp(
+        theme: new ThemeData(platform: TargetPlatform.iOS),
+        routes: routes,
+      ),
+    );
+    await tester.tap(find.text('PUSH'));
+    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 2);
+    expect(find.text('PUSH'), findsNothing);
+    expect(find.text('HELLO'), findsOneWidget);
+    final Offset helloPosition1 = tester.getCenter(find.text('HELLO'));
+    final TestGesture gesture = await tester.startGesture(const Offset(2.5, 300.0));
+    await tester.pump(const Duration(milliseconds: 20));
+    await gesture.moveBy(const Offset(100.0, 0.0));
+    expect(find.text('PUSH'), findsNothing);
+    expect(find.text('HELLO'), findsOneWidget);
+    await tester.pump(const Duration(milliseconds: 20));
+    expect(find.text('PUSH'), findsOneWidget);
+    expect(find.text('HELLO'), findsOneWidget);
+    final Offset helloPosition2 = tester.getCenter(find.text('HELLO'));
+    expect(helloPosition1.dx, lessThan(helloPosition2.dx));
+    expect(helloPosition1.dy, helloPosition2.dy);
+    expect(Theme.of(tester.element(find.text('HELLO'))).platform, TargetPlatform.iOS);
+    await tester.pumpWidget(
+      new MaterialApp(
+        theme: new ThemeData(platform: TargetPlatform.android),
+        routes: routes,
+      ),
+    );
+    // Now we have to let the theme animation run through.
+    // This takes three frames (including the first one above):
+    //  1. Start the Theme animation. It's at t=0 so everything else is identical.
+    //  2. Start any animations that are informed by the Theme, for example, the
+    //     DefaultTextStyle, on the first frame that the theme is not at t=0. In
+    //     this case, it's at t=1.0 of the theme animation, so this is also the
+    //     frame in which the theme animation ends.
+    //  3. End all the other animations.
+    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 2);
+    expect(Theme.of(tester.element(find.text('HELLO'))).platform, TargetPlatform.android);
+    final Offset helloPosition3 = tester.getCenter(find.text('HELLO'));
+    expect(helloPosition3, helloPosition2);
+    expect(find.text('PUSH'), findsOneWidget);
+    expect(find.text('HELLO'), findsOneWidget);
+    await gesture.moveBy(const Offset(100.0, 0.0));
+    await tester.pump(const Duration(milliseconds: 20));
+    expect(find.text('PUSH'), findsOneWidget);
+    expect(find.text('HELLO'), findsOneWidget);
+    final Offset helloPosition4 = tester.getCenter(find.text('HELLO'));
+    expect(helloPosition3.dx, lessThan(helloPosition4.dx));
+    expect(helloPosition3.dy, helloPosition4.dy);
+    await gesture.moveBy(const Offset(500.0, 0.0));
+    await gesture.up();
+    expect(await tester.pumpAndSettle(const Duration(minutes: 1)), 2);
+    expect(find.text('PUSH'), findsOneWidget);
+    expect(find.text('HELLO'), findsNothing);
+  });
+
   testWidgets('test no back gesture on iOS fullscreen dialogs', (WidgetTester tester) async {
     await tester.pumpWidget(
       new MaterialApp(

packages/flutter/test/widgets/page_transitions_test.dart

@@ -268,24 +268,39 @@ void main() {
     expect(find.text('Home'), findsNothing);
     expect(find.text('Sheet'), isOnstage);
 
+    // Drag from left edge to invoke the gesture. We should go back.
+    TestGesture gesture = await tester.startGesture(const Offset(5.0, 100.0));
+    await gesture.moveBy(const Offset(500.0, 0.0));
+    await gesture.up();
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    Navigator.pushNamed(containerKey1.currentContext, '/sheet');
+
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(find.text('Home'), findsNothing);
+    expect(find.text('Sheet'), isOnstage);
+
     // Show the bottom sheet.
     final PersistentBottomSheetTestState sheet = containerKey2.currentState;
     sheet.showBottomSheet();
 
     await tester.pump(const Duration(seconds: 1));
 
-    // Drag from left edge to invoke the gesture.
-    final TestGesture gesture = await tester.startGesture(const Offset(5.0, 100.0));
+    // Drag from left edge to invoke the gesture. Nothing should happen.
+    gesture = await tester.startGesture(const Offset(5.0, 100.0));
     await gesture.moveBy(const Offset(500.0, 0.0));
     await gesture.up();
     await tester.pump();
     await tester.pump(const Duration(seconds: 1));
 
-    expect(find.text('Home'), isOnstage);
-    expect(find.text('Sheet'), findsNothing);
+    expect(find.text('Home'), findsNothing);
+    expect(find.text('Sheet'), isOnstage);
 
-    // Sheet called setState and didn't crash.
-    expect(sheet.setStateCalled, isTrue);
+    // Sheet did not call setState (since the gesture did nothing).
+    expect(sheet.setStateCalled, isFalse);
   });
 
   testWidgets('Test completed future', (WidgetTester tester) async {