Merge pull request #750 from Hixie/yak3-performance-view-listener-refactor

Refactor PerformanceView listeners.

packages/flutter/lib/animation.dart

@@ -8,10 +8,11 @@
 library animation;
 
 export 'src/animation/animated_value.dart';
-export 'src/animation/performance.dart';
 export 'src/animation/clamped_simulation.dart';
 export 'src/animation/curves.dart';
 export 'src/animation/forces.dart';
+export 'src/animation/listener_helpers.dart';
+export 'src/animation/performance.dart';
 export 'src/animation/scroll_behavior.dart';
 export 'src/animation/simulation_stepper.dart';
 export 'src/animation/ticker.dart';

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

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ui' show VoidCallback;
+
+/// The status of an animation
+enum PerformanceStatus {
+  /// The animation is stopped at the beginning
+  dismissed,
+
+  /// The animation is running from beginning to end
+  forward,
+
+  /// The animation is running backwards, from end to beginning
+  reverse,
+
+  /// The animation is stopped at the end
+  completed,
+}
+
+typedef void PerformanceStatusListener(PerformanceStatus status);
+
+abstract class _ListenerMixin {
+  void didRegisterListener();
+  void didUnregisterListener();
+}
+
+abstract class LazyListenerMixin implements _ListenerMixin {
+  int _listenerCounter = 0;
+  void didRegisterListener() {
+    assert(_listenerCounter >= 0);
+    if (_listenerCounter == 0)
+      didStartListening();
+    _listenerCounter += 1;
+  }
+  void didUnregisterListener() {
+    assert(_listenerCounter >= 1);
+    _listenerCounter -= 1;
+    if (_listenerCounter == 0)
+      didStopListening();
+  }
+  void didStartListening();
+  void didStopListening();
+  bool get isListening => _listenerCounter > 0;
+}
+
+abstract class EagerListenerMixin implements _ListenerMixin {
+  void didRegisterListener() { }
+  void didUnregisterListener() { }
+
+  /// Release any resources used by this object.
+  void dispose();
+}
+
+abstract class LocalPerformanceListenersMixin extends _ListenerMixin {
+  final List<VoidCallback> _listeners = <VoidCallback>[];
+  void addListener(VoidCallback listener) {
+    didRegisterListener();
+    _listeners.add(listener);
+  }
+  void removeListener(VoidCallback listener) {
+    _listeners.remove(listener);
+    didUnregisterListener();
+  }
+  void notifyListeners() {
+    List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners);
+    for (VoidCallback listener in localListeners)
+      listener();
+  }
+}
+
+abstract class LocalPerformanceStatusListenersMixin extends _ListenerMixin {
+  final List<PerformanceStatusListener> _statusListeners = <PerformanceStatusListener>[];
+  void addStatusListener(PerformanceStatusListener listener) {
+    didRegisterListener();
+    _statusListeners.add(listener);
+  }
+  void removeStatusListener(PerformanceStatusListener listener) {
+    _statusListeners.remove(listener);
+    didUnregisterListener();
+  }
+  void notifyStatusListeners(PerformanceStatus status) {
+    List<PerformanceStatusListener> localListeners = new List<PerformanceStatusListener>.from(_statusListeners);
+    for (PerformanceStatusListener listener in localListeners)
+      listener(status);
+  }
+}

packages/unit/test/widget/page_forward_transitions_test.dart

@@ -13,7 +13,9 @@ class TestTransition extends TransitionComponent {
     this.childFirstHalf,
     this.childSecondHalf,
     PerformanceView performance
-  }) : super(key: key, performance: performance);
+  }) : super(key: key, performance: performance) {
+    assert(performance != null);
+  }
 
   final Widget childFirstHalf;
   final Widget childSecondHalf;