showSnackBar() returns a Future, clears its placeholder

TransitionRoute completer is now optional.

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

@@ -77,10 +77,14 @@ class _BottomSheetRoute extends OverlayRoute {
   }
 
   void didPop(dynamic result) {
-    completer.complete(result);
-    performance.reverse().then((_) {
+    void finish() {
       super.didPop(result); // clear the overlay entries
-    });
+      completer.complete(result);
+    }
+    if (performance.isDismissed)
+      finish();
+    else
+      performance.reverse().then((_) { finish(); });
   }
 
   String get debugLabel => '$runtimeType';

packages/flutter/lib/src/material/snack_bar.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 'dart:async';
+
 import 'package:flutter/animation.dart';
 import 'package:flutter/widgets.dart';
 
@@ -92,12 +94,15 @@ class _SnackBar extends StatelessComponent {
 }
 
 class _SnackBarRoute extends TransitionRoute {
+  _SnackBarRoute({ Completer completer }) : super(completer: completer);
+
   bool get opaque => false;
   Duration get transitionDuration => const Duration(milliseconds: 200);
 }
 
-void showSnackBar({ BuildContext context, GlobalKey<PlaceholderState> placeholderKey, Widget content, List<SnackBarAction> actions }) {
-  _SnackBarRoute route = new _SnackBarRoute();
+Future showSnackBar({ BuildContext context, GlobalKey<PlaceholderState> placeholderKey, Widget content, List<SnackBarAction> actions }) {
+  final Completer completer = new Completer();
+  _SnackBarRoute route = new _SnackBarRoute(completer: completer);
   _SnackBar snackBar = new _SnackBar(
     route: route,
     content: content,
@@ -105,4 +110,7 @@ void showSnackBar({ BuildContext context, GlobalKey<PlaceholderState> placeholde
   );
   placeholderKey.currentState.child = snackBar;
   Navigator.of(context).pushEphemeral(route);
+  return completer.future.then((_) {
+    placeholderKey.currentState.child = null;
+  });
 }

packages/flutter/lib/src/widgets/routes.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 'dart:async';
+
 import 'package:flutter/animation.dart';
 
 import 'basic.dart';
@@ -46,6 +48,10 @@ class OverlayRoute extends Route {
 
 // TODO(abarth): Should we add a type for the result?
 abstract class TransitionRoute extends OverlayRoute {
+  TransitionRoute({ this.completer });
+
+  final Completer completer;
+
   Duration get transitionDuration;
   bool get opaque;
 
@@ -86,7 +92,10 @@ abstract class TransitionRoute extends OverlayRoute {
 
   void didPop(dynamic result) {
     _result = result;
-    _performance.reverse();
+    if (completer != null)
+      _performance.reverse().then((_) { completer.complete(_result); });
+    else
+      _performance.reverse();
   }
 
   String get debugLabel => '$runtimeType';

packages/unit/test/widget/bottom_sheet_test.dart

@@ -8,6 +8,8 @@ void main() {
   test('Verify that a tap dismisses a modal BottomSheet', () {
     testWidgets((WidgetTester tester) {
       BuildContext context;
+      bool showBottomSheetThenCalled = false;
+
       tester.pumpWidget(new MaterialApp(
           routes: <String, RouteBuilder>{
             '/': (RouteArguments args) {
@@ -20,7 +22,10 @@ void main() {
       tester.pump();
       expect(tester.findText('BottomSheet'), isNull);
 
-      showModalBottomSheet(context: context, child: new Text('BottomSheet'));
+      showModalBottomSheet(context: context, child: new Text('BottomSheet')).then((_) {
+        showBottomSheetThenCalled = true;
+      });
+
       tester.pump(); // bottom sheet show animation starts
       tester.pump(new Duration(seconds: 1)); // animation done
       expect(tester.findText('BottomSheet'), isNotNull);
@@ -29,7 +34,8 @@ void main() {
       tester.tap(tester.findText('BottomSheet'));
       tester.pump(); // bottom sheet dismiss animation starts
       tester.pump(new Duration(seconds: 1)); // animation done
-      tester.pump(new Duration(seconds: 2)); // rebuild frame
+      tester.pump(new Duration(seconds: 1)); // rebuild frame
+      expect(showBottomSheetThenCalled, isTrue);
       expect(tester.findText('BottomSheet'), isNull);
 
       showModalBottomSheet(context: context, child: new Text('BottomSheet'));
@@ -41,7 +47,7 @@ void main() {
       tester.tapAt(new Point(20.0, 20.0));
       tester.pump(); // bottom sheet dismiss animation starts
       tester.pump(new Duration(seconds: 1)); // animation done
-      tester.pump(new Duration(seconds: 2)); // rebuild frame
+      tester.pump(new Duration(seconds: 1)); // rebuild frame
       expect(tester.findText('BottomSheet'), isNull);
     });
   });
@@ -50,6 +56,8 @@ void main() {
     testWidgets((WidgetTester tester) {
       GlobalKey<PlaceholderState> _bottomSheetPlaceholderKey = new GlobalKey<PlaceholderState>();
       BuildContext context;
+      bool showBottomSheetThenCalled = false;
+
       tester.pumpWidget(new MaterialApp(
           routes: <String, RouteBuilder>{
             '/': (RouteArguments args) {
@@ -69,7 +77,9 @@ void main() {
         context: context,
         child: new Container(child: new Text('BottomSheet'), margin: new EdgeDims.all(40.0)),
         placeholderKey: _bottomSheetPlaceholderKey
-      );
+      ).then((_) {
+        showBottomSheetThenCalled = true;
+      });
 
       expect(_bottomSheetPlaceholderKey.currentState.child, isNotNull);
       tester.pump(); // bottom sheet show animation starts
@@ -79,7 +89,8 @@ void main() {
       tester.fling(tester.findText('BottomSheet'), const Offset(0.0, 20.0), 1000.0);
       tester.pump(); // bottom sheet dismiss animation starts
       tester.pump(new Duration(seconds: 1)); // animation done
-      tester.pump(new Duration(seconds: 2)); // rebuild frame without the bottom sheet
+      tester.pump(new Duration(seconds: 1)); // rebuild frame without the bottom sheet
+      expect(showBottomSheetThenCalled, isTrue);
       expect(tester.findText('BottomSheet'), isNull);
       expect(_bottomSheetPlaceholderKey.currentState.child, isNull);
     });

packages/unit/test/widget/snack_bar_test.dart

@@ -9,17 +9,22 @@ void main() {
       String helloSnackBar = 'Hello SnackBar';
       GlobalKey<PlaceholderState> placeholderKey = new GlobalKey<PlaceholderState>();
       Key tapTarget = new Key('tap-target');
+      BuildContext context;
+      bool showSnackBarThenCalled = false;
 
       tester.pumpWidget(new MaterialApp(
         routes: <String, RouteBuilder>{
           '/': (RouteArguments args) {
+            context = args.context;
             return new GestureDetector(
               onTap: () {
                 showSnackBar(
                   context: args.context,
                   placeholderKey: placeholderKey,
                   content: new Text(helloSnackBar)
-                );
+                ).then((_) {
+                  showSnackBarThenCalled = true;
+                });
               },
               child: new Container(
                 decoration: const BoxDecoration(
@@ -36,10 +41,16 @@ void main() {
       ));
 
       tester.tap(tester.findElementByKey(tapTarget));
-
       expect(tester.findText(helloSnackBar), isNull);
       tester.pump();
       expect(tester.findText(helloSnackBar), isNotNull);
+
+      Navigator.of(context).pop();
+      expect(tester.findText(helloSnackBar), isNotNull);
+      tester.pump(new Duration(seconds: 1));
+      expect(showSnackBarThenCalled, isTrue);
+      expect(tester.findText(helloSnackBar), isNull);
+      expect(placeholderKey.currentState.child, isNull);
     });
   });
 }