Change PageController#nextPage & #previousPage methods to return Future when...

Change PageController#nextPage & #previousPage methods to return Future when the animation completes. (#12299)

* Changed PageController #nextPage & #previousPage to return a Future after completing.

* Removed false statement about returning a Future in PageController#jumpToPage

* Added tests to make sure nextPage & previousPage return Futures.

* Tested that the Futures returned by nextPage & previousPage actually resolve.

* Renaming *pageCalled to *pageCompleted, since that's what it's actually for.

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

@@ -114,8 +114,8 @@ class PageController extends ScrollController {
   /// The returned [Future] resolves when the animation completes.
   ///
   /// The `duration` and `curve` arguments must not be null.
-  void nextPage({ @required Duration duration, @required Curve curve }) {
-    animateToPage(page.round() + 1, duration: duration, curve: curve);
+  Future<Null> nextPage({ @required Duration duration, @required Curve curve }) {
+    return animateToPage(page.round() + 1, duration: duration, curve: curve);
   }
 
   /// Animates the controlled [PageView] to the previous page.
@@ -124,8 +124,8 @@ class PageController extends ScrollController {
   /// The returned [Future] resolves when the animation completes.
   ///
   /// The `duration` and `curve` arguments must not be null.
-  void previousPage({ @required Duration duration, @required Curve curve }) {
-    animateToPage(page.round() - 1, duration: duration, curve: curve);
+  Future<Null> previousPage({ @required Duration duration, @required Curve curve }) {
+    return animateToPage(page.round() - 1, duration: duration, curve: curve);
   }
 
   @override

packages/flutter/test/widgets/page_view_test.dart

@@ -211,6 +211,38 @@ void main() {
     expect(find.text('Arizona'), findsOneWidget);
   });
 
+  testWidgets('PageController nextPage and previousPage return Futures that resolve', (WidgetTester tester) async {
+    final PageController controller = new PageController();
+    await tester.pumpWidget(new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new PageView(
+          controller: controller,
+          children: kStates.map<Widget>((String state) => new Text(state)).toList(),
+        ),
+    ));
+
+    bool nextPageCompleted = false;
+    controller.nextPage(duration: const Duration(milliseconds: 150), curve: Curves.ease)
+        .then((_) => nextPageCompleted = true);
+
+    expect(nextPageCompleted, false);
+    await tester.pump(const Duration(milliseconds: 200));
+    expect(nextPageCompleted, false);
+    await tester.pump(const Duration(milliseconds: 200));
+    expect(nextPageCompleted, true);
+
+
+    bool previousPageCompleted = false;
+    controller.previousPage(duration: const Duration(milliseconds: 150), curve: Curves.ease)
+        .then((_) => previousPageCompleted = true);
+
+    expect(previousPageCompleted, false);
+    await tester.pump(const Duration(milliseconds: 200));
+    expect(previousPageCompleted, false);
+    await tester.pump(const Duration(milliseconds: 200));
+    expect(previousPageCompleted, true);
+  });
+
   testWidgets('PageView in zero-size container', (WidgetTester tester) async {
     await tester.pumpWidget(new Directionality(
       textDirection: TextDirection.ltr,