[animations] Support for returning value from popped route

packages/animations/example/lib/container_transition.dart

@@ -49,6 +49,10 @@ class OpenContainerTransformDemo extends StatefulWidget {
 class _OpenContainerTransformDemoState
     extends State<OpenContainerTransformDemo> {
   ContainerTransitionType _transitionType = ContainerTransitionType.fade;
+  final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();
+
+  static int doneCounter = 0;
+  final ValueKey<int> counterKey = ValueKey<int>(doneCounter);
 
   void _showSettingsBottomModalSheet(BuildContext context) {
     showModalBottomSheet<void>(
@@ -103,6 +107,7 @@ class _OpenContainerTransformDemoState
   @override
   Widget build(BuildContext context) {
     return Scaffold(
+      key: scaffoldKey,
       appBar: AppBar(
         title: const Text('Container transform'),
         actions: <Widget>[
@@ -117,18 +122,63 @@ class _OpenContainerTransformDemoState
       body: ListView(
         padding: const EdgeInsets.all(8.0),
         children: <Widget>[
+          Container(
+            key: counterKey,
+            padding: const EdgeInsets.symmetric(
+              vertical: 15.0,
+              horizontal: 10.0,
+            ),
+            margin: const EdgeInsets.only(bottom: 10.0),
+            decoration: BoxDecoration(
+              color: Colors.purple[100],
+              borderRadius: BorderRadius.circular(5.0),
+            ),
+            child: Row(
+              children: <Widget>[
+                const Padding(
+                  padding: EdgeInsets.only(right: 10.0),
+                  child: Icon(Icons.done),
+                ),
+                RichText(
+                  text: TextSpan(
+                    style: const TextStyle(fontSize: 18.0, color: Colors.black),
+                    children: <TextSpan>[
+                      const TextSpan(text: 'Marked as done '),
+                      TextSpan(
+                        text: '$doneCounter',
+                        style: const TextStyle(fontWeight: FontWeight.bold),
+                      ),
+                      const TextSpan(text: ' times'),
+                    ],
+                  ),
+                ),
+              ],
+            ),
+          ),
           _OpenContainerWrapper(
             transitionType: _transitionType,
             closedBuilder: (BuildContext _, VoidCallback openContainer) {
               return _ExampleCard(openContainer: openContainer);
             },
+            onClosed: (bool isMarkedAsDone) {
+              if (isMarkedAsDone)
+                setState(() {
+                  doneCounter++;
+                });
+            },
           ),
           const SizedBox(height: 16.0),
           _OpenContainerWrapper(
             transitionType: _transitionType,
             closedBuilder: (BuildContext _, VoidCallback openContainer) {
               return _ExampleSingleTile(openContainer: openContainer);
             },
+            onClosed: (bool isMarkedAsDone) {
+              if (isMarkedAsDone)
+                setState(() {
+                  doneCounter++;
+                });
+            },
           ),
           const SizedBox(height: 16.0),
           Row(
@@ -142,6 +192,12 @@ class _OpenContainerTransformDemoState
                       subtitle: 'Secondary text',
                     );
                   },
+                  onClosed: (bool isMarkedAsDone) {
+                    if (isMarkedAsDone)
+                      setState(() {
+                        doneCounter++;
+                      });
+                  },
                 ),
               ),
               const SizedBox(width: 8.0),
@@ -154,6 +210,12 @@ class _OpenContainerTransformDemoState
                       subtitle: 'Secondary text',
                     );
                   },
+                  onClosed: (bool isMarkedAsDone) {
+                    if (isMarkedAsDone)
+                      setState(() {
+                        doneCounter++;
+                      });
+                  },
                 ),
               ),
             ],
@@ -170,6 +232,12 @@ class _OpenContainerTransformDemoState
                       subtitle: 'Secondary',
                     );
                   },
+                  onClosed: (bool isMarkedAsDone) {
+                    if (isMarkedAsDone)
+                      setState(() {
+                        doneCounter++;
+                      });
+                  },
                 ),
               ),
               const SizedBox(width: 8.0),
@@ -182,6 +250,12 @@ class _OpenContainerTransformDemoState
                       subtitle: 'Secondary',
                     );
                   },
+                  onClosed: (bool isMarkedAsDone) {
+                    if (isMarkedAsDone)
+                      setState(() {
+                        doneCounter++;
+                      });
+                  },
                 ),
               ),
               const SizedBox(width: 8.0),
@@ -194,17 +268,34 @@ class _OpenContainerTransformDemoState
                       subtitle: 'Secondary',
                     );
                   },
+                  onClosed: (bool isMarkedAsDone) {
+                    if (isMarkedAsDone)
+                      setState(() {
+                        doneCounter++;
+                      });
+                  },
                 ),
               ),
             ],
           ),
           const SizedBox(height: 16.0),
           ...List<Widget>.generate(10, (int index) {
-            return OpenContainer(
+            return OpenContainer<bool>(
               transitionType: _transitionType,
               openBuilder: (BuildContext _, VoidCallback openContainer) {
                 return _DetailsPage();
               },
+              onClosed: (bool isMarkedAsDone) {
+                if (isMarkedAsDone) {
+                  scaffoldKey.currentState.showSnackBar(const SnackBar(
+                    content: Text('Marked as done!'),
+                  ));
+
+                  setState(() {
+                    doneCounter++;
+                  });
+                }
+              },
               tappable: false,
               closedShape: const RoundedRectangleBorder(),
               closedElevation: 0.0,
@@ -223,7 +314,7 @@ class _OpenContainerTransformDemoState
           }),
         ],
       ),
-      floatingActionButton: OpenContainer(
+      floatingActionButton: OpenContainer<bool>(
         transitionType: _transitionType,
         openBuilder: (BuildContext context, VoidCallback _) {
           return _DetailsPage();
@@ -235,6 +326,12 @@ class _OpenContainerTransformDemoState
           ),
         ),
         closedColor: Theme.of(context).colorScheme.secondary,
+        onClosed: (bool isMarkedAsDone) {
+          if (isMarkedAsDone)
+            setState(() {
+              doneCounter++;
+            });
+        },
         closedBuilder: (BuildContext context, VoidCallback openContainer) {
           return SizedBox(
             height: _fabDimension,
@@ -256,18 +353,21 @@ class _OpenContainerWrapper extends StatelessWidget {
   const _OpenContainerWrapper({
     this.closedBuilder,
     this.transitionType,
+    this.onClosed,
   });
 
   final OpenContainerBuilder closedBuilder;
   final ContainerTransitionType transitionType;
+  final onClosedCallback<bool> onClosed;
 
   @override
   Widget build(BuildContext context) {
-    return OpenContainer(
+    return OpenContainer<bool>(
       transitionType: transitionType,
       openBuilder: (BuildContext context, VoidCallback _) {
         return _DetailsPage();
       },
+      onClosed: onClosed,
       tappable: false,
       closedBuilder: closedBuilder,
     );
@@ -456,7 +556,16 @@ class _DetailsPage extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-      appBar: AppBar(title: const Text('Details page')),
+      appBar: AppBar(
+        title: const Text('Details page'),
+        actions: <Widget>[
+          IconButton(
+            icon: const Icon(Icons.done),
+            onPressed: () => Navigator.pop(context, true),
+            tooltip: 'Mark as done',
+          )
+        ],
+      ),
       body: ListView(
         children: <Widget>[
           Container(

packages/animations/lib/src/open_container.dart

@@ -29,6 +29,10 @@ enum ContainerTransitionType {
   fadeThrough,
 }
 
+/// Callback function which is called when the [OpenContainer]
+/// is closed.
+typedef onClosedCallback<S> = void Function(S data);
+
 /// A container that grows to fill the screen to reveal new content when tapped.
 ///
 /// While the container is closed, it shows the [Widget] returned by
@@ -45,17 +49,21 @@ enum ContainerTransitionType {
 /// [closedBuilder] exist in the tree at the same time. Therefore, the widgets
 /// returned by these builders cannot include the same global key.
 ///
+/// `T` refers to the type of data returned by the route when the container
+/// is closed. This value can be accessed in the `onClosed` function.
+///
 // TODO(goderbauer): Add example animations and sample code.
 ///
 /// See also:
 ///
 ///  * [Transitions with animated containers](https://material.io/design/motion/choreography.html#transformation)
 ///    in the Material spec.
-class OpenContainer extends StatefulWidget {
+@optionalTypeArgs
+class OpenContainer<T> extends StatefulWidget {
   /// Creates an [OpenContainer].
   ///
   /// All arguments except for [key] must not be null. The arguments
-  /// [closedBuilder] and [closedBuilder] are required.
+  /// [openBuilder] and [closedBuilder] are required.
   const OpenContainer({
     Key key,
     this.closedColor = Colors.white,
@@ -167,7 +175,9 @@ class OpenContainer extends StatefulWidget {
   final ShapeBorder openShape;
 
   /// Called when the container was popped and has returned to the closed state.
-  final VoidCallback onClosed;
+  /// The return value from the popped screen is passed to this function as an
+  /// argument.
+  final onClosedCallback<T> onClosed;
 
   /// Called to obtain the child for the container in the closed state.
   ///
@@ -218,10 +228,10 @@ class OpenContainer extends StatefulWidget {
   final bool useRootNavigator;
 
   @override
-  _OpenContainerState createState() => _OpenContainerState();
+  _OpenContainerState<T> createState() => _OpenContainerState<T>();
 }
 
-class _OpenContainerState extends State<OpenContainer> {
+class _OpenContainerState<T> extends State<OpenContainer<T>> {
   // Key used in [_OpenContainerRoute] to hide the widget returned by
   // [OpenContainer.openBuilder] in the source route while the container is
   // opening/open. A copy of that widget is included in the
@@ -235,8 +245,9 @@ class _OpenContainerState extends State<OpenContainer> {
   final GlobalKey _closedBuilderKey = GlobalKey();
 
   Future<void> openContainer() async {
-    await Navigator.of(context, rootNavigator: widget.useRootNavigator)
-        .push(_OpenContainerRoute(
+    final T data =
+        await Navigator.of(context, rootNavigator: widget.useRootNavigator)
+            .push(_OpenContainerRoute<T>(
       closedColor: widget.closedColor,
       openColor: widget.openColor,
       closedElevation: widget.closedElevation,
@@ -251,7 +262,7 @@ class _OpenContainerState extends State<OpenContainer> {
       transitionType: widget.transitionType,
     ));
     if (widget.onClosed != null) {
-      widget.onClosed();
+      widget.onClosed(data);
     }
   }
 
@@ -347,7 +358,7 @@ class _HideableState extends State<_Hideable> {
   }
 }
 
-class _OpenContainerRoute extends ModalRoute<void> {
+class _OpenContainerRoute<T> extends ModalRoute<T> {
   _OpenContainerRoute({
     @required this.closedColor,
     @required this.openColor,
@@ -580,7 +591,7 @@ class _OpenContainerRoute extends ModalRoute<void> {
   }
 
   @override
-  bool didPop(void result) {
+  bool didPop(T result) {
     _takeMeasurements(
       navigatorContext: subtreeContext,
       delayForSourceRoute: true,