Merge pull request #2235 from abarth/animation_status

Elide fewer AnimationStatus callbacks

packages/flutter/lib/src/animation/animation_controller.dart

@@ -146,6 +146,7 @@ class AnimationController extends Animation<double>
     stop();
     if (simulationDuration == Duration.ZERO) {
       assert(value == target);
+      _checkStatusChanged();
       return new Future.value();
     }
     assert(simulationDuration > Duration.ZERO);
@@ -180,7 +181,9 @@ class AnimationController extends Animation<double>
     assert(!isAnimating);
     _simulation = simulation;
     _value = simulation.x(0.0).clamp(lowerBound, upperBound);
-    return _ticker.start();
+    Future result = _ticker.start();
+    _checkStatusChanged();
+    return result;
   }
 
   /// Stops running this animation.
@@ -194,13 +197,13 @@ class AnimationController extends Animation<double>
     stop();
   }
 
-  AnimationStatus _lastStatus = AnimationStatus.dismissed;
+  AnimationStatus _lastReportedStatus = AnimationStatus.dismissed;
   void _checkStatusChanged() {
     AnimationStatus newStatus = status;
-    AnimationStatus oldStatus = _lastStatus;
-    _lastStatus = newStatus;
-    if (oldStatus != newStatus)
+    if (_lastReportedStatus != newStatus) {
+      _lastReportedStatus = newStatus;
       notifyStatusListeners(newStatus);
+    }
   }
 
   void _tick(Duration elapsed) {

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

@@ -22,9 +22,9 @@ class OverlayEntry {
   bool get opaque => _opaque;
   bool _opaque;
   void set opaque (bool value) {
-    assert(_overlay != null);
     if (_opaque == value)
       return;
+    assert(_overlay != null);
     _overlay.setState(() {
       _opaque = value;
     });

packages/flutter/test/animation/animation_controller_test.dart

@@ -36,5 +36,70 @@ void main() {
     Scheduler.instance.handleBeginFrame(const Duration(seconds: 2));
     expect(didComplete, isTrue);
     expect(didDismiss, isTrue);
+
+    controller.stop();
+  });
+
+  test("Receives status callbacks for forward and reverse", () {
+    WidgetFlutterBinding.ensureInitialized();
+    AnimationController controller = new AnimationController(
+      duration: const Duration(milliseconds: 100)
+    );
+    List<double> valueLog = <double>[];
+    List<AnimationStatus> log = <AnimationStatus>[];
+    controller
+      ..addStatusListener((AnimationStatus status) {
+        log.add(status);
+      })
+      ..addListener(() {
+        valueLog.add(controller.value);
+      });
+
+    expect(log, equals([]));
+    expect(valueLog, equals([]));
+
+    controller.forward();
+
+    expect(log, equals([AnimationStatus.forward]));
+    expect(valueLog, equals([]));
+
+    controller.reverse();
+
+    expect(log, equals([AnimationStatus.forward, AnimationStatus.dismissed]));
+    expect(valueLog, equals([]));
+
+    controller.reverse();
+
+    expect(log, equals([AnimationStatus.forward, AnimationStatus.dismissed]));
+    expect(valueLog, equals([]));
+
+    log.clear();
+    controller.forward();
+
+    expect(log, equals([AnimationStatus.forward]));
+    expect(valueLog, equals([]));
+
+    controller.forward();
+
+    expect(log, equals([AnimationStatus.forward]));
+    expect(valueLog, equals([]));
+
+    controller.reverse();
+    log.clear();
+
+    Scheduler.instance.handleBeginFrame(const Duration(seconds: 10));
+    expect(log, equals([]));
+    expect(valueLog, equals([]));
+    Scheduler.instance.handleBeginFrame(const Duration(seconds: 20));
+    expect(log, equals([]));
+    expect(valueLog, equals([]));
+    Scheduler.instance.handleBeginFrame(const Duration(seconds: 30));
+    expect(log, equals([]));
+    expect(valueLog, equals([]));
+    Scheduler.instance.handleBeginFrame(const Duration(seconds: 40));
+    expect(log, equals([]));
+    expect(valueLog, equals([]));
+
+    controller.stop();
   });
 }