Revert "Strengthen animation listener iteration patterns" (#7552)

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

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:collection';
 import 'dart:ui' show VoidCallback;
 
 import 'package:flutter/foundation.dart';
@@ -35,11 +34,9 @@ abstract class AnimationLazyListenerMixin implements _ListenerMixin {
   }
 
   /// Called when the number of listeners changes from zero to one.
-  @protected
   void didStartListening();
 
   /// Called when the number of listeners changes from one to zero.
-  @protected
   void didStopListening();
 
   /// Whether there are any listeners.
@@ -64,7 +61,7 @@ abstract class AnimationEagerListenerMixin implements _ListenerMixin {
 /// A mixin that implements the addListener/removeListener protocol and notifies
 /// all the registered listeners when notifyListeners is called.
 abstract class AnimationLocalListenersMixin extends _ListenerMixin {
-  final Set<VoidCallback> _listeners = new LinkedHashSet<VoidCallback>();
+  final List<VoidCallback> _listeners = <VoidCallback>[];
 
   /// Calls the listener every time the value of the animation changes.
   ///
@@ -87,24 +84,9 @@ abstract class AnimationLocalListenersMixin extends _ListenerMixin {
   /// If listeners are added or removed during this function, the modifications
   /// will not change which listeners are called during this iteration.
   void notifyListeners() {
-    final List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners);
-    for (VoidCallback listener in localListeners) {
-      try {
-        if (_listeners.contains(listener))
-          listener();
-      } catch (exception, stack) {
-        FlutterError.reportError(new FlutterErrorDetails(
-          exception: exception,
-          stack: stack,
-          library: 'animation library',
-          context: 'while notifying listeners for $runtimeType',
-          informationCollector: (StringBuffer information) {
-            information.writeln('The $runtimeType notifying listeners was:');
-            information.write('  $this');
-          }
-        ));
-      }
-    }
+    List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners);
+    for (VoidCallback listener in localListeners)
+      listener();
   }
 }
 
@@ -112,7 +94,7 @@ abstract class AnimationLocalListenersMixin extends _ListenerMixin {
 /// and notifies all the registered listeners when notifyStatusListeners is
 /// called.
 abstract class AnimationLocalStatusListenersMixin extends _ListenerMixin {
-  final Set<AnimationStatusListener> _statusListeners = new LinkedHashSet<AnimationStatusListener>();
+  final List<AnimationStatusListener> _statusListeners = <AnimationStatusListener>[];
 
   /// Calls listener every time the status of the animation changes.
   ///
@@ -135,23 +117,8 @@ abstract class AnimationLocalStatusListenersMixin extends _ListenerMixin {
   /// If listeners are added or removed during this function, the modifications
   /// will not change which listeners are called during this iteration.
   void notifyStatusListeners(AnimationStatus status) {
-    final List<AnimationStatusListener> localListeners = new List<AnimationStatusListener>.from(_statusListeners);
-    for (AnimationStatusListener listener in localListeners) {
-      try {
-        if (_statusListeners.contains(listener))
-          listener(status);
-      } catch (exception, stack) {
-        FlutterError.reportError(new FlutterErrorDetails(
-          exception: exception,
-          stack: stack,
-          library: 'animation library',
-          context: 'while notifying status listeners for $runtimeType',
-          informationCollector: (StringBuffer information) {
-            information.writeln('The $runtimeType notifying status listeners was:');
-            information.write('  $this');
-          }
-        ));
-      }
-    }
+    List<AnimationStatusListener> localListeners = new List<AnimationStatusListener>.from(_statusListeners);
+    for (AnimationStatusListener listener in localListeners)
+      listener(status);
   }
 }

packages/flutter/lib/src/foundation/change_notifier.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:collection';
-
 import 'package:meta/meta.dart';
 
 import 'assertions.dart';
@@ -39,11 +37,11 @@ abstract class Listenable {
 /// It is O(N) for adding and removing listeners and O(N²) for dispatching
 /// notifications (where N is the number of listeners).
 class ChangeNotifier extends Listenable {
-  Set<VoidCallback> _listeners = new LinkedHashSet<VoidCallback>();
+  List<VoidCallback> _listeners;
 
   bool _debugAssertNotDisposed() {
     assert(() {
-      if (_listeners == null) {
+      if (_listeners == const <VoidCallback>[]) {
         throw new FlutterError(
           'A $runtimeType was used after being disposed.\n'
           'Once you have called dispose() on a $runtimeType, it can no longer be used.'
@@ -60,6 +58,7 @@ class ChangeNotifier extends Listenable {
   @override
   void addListener(VoidCallback listener) {
     assert(_debugAssertNotDisposed);
+    _listeners ??= <VoidCallback>[];
     _listeners.add(listener);
   }
 
@@ -72,7 +71,7 @@ class ChangeNotifier extends Listenable {
   @override
   void removeListener(VoidCallback listener) {
     assert(_debugAssertNotDisposed);
-    _listeners.remove(listener);
+    _listeners?.remove(listener);
   }
 
   /// Discards any resources used by the object. After this is called, the
@@ -84,7 +83,7 @@ class ChangeNotifier extends Listenable {
   @mustCallSuper
   void dispose() {
     assert(_debugAssertNotDisposed);
-    _listeners = null;
+    _listeners = const <VoidCallback>[];
   }
 
   /// Call all the registered listeners.
@@ -102,7 +101,7 @@ class ChangeNotifier extends Listenable {
   void notifyListeners() {
     assert(_debugAssertNotDisposed);
     if (_listeners != null) {
-      final List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners);
+      List<VoidCallback> localListeners = new List<VoidCallback>.from(_listeners);
       for (VoidCallback listener in localListeners) {
         try {
           if (_listeners.contains(listener))

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

@@ -167,6 +167,14 @@ class _CupertinoBackGestureController extends NavigationGestureController {
   }
 
   void handleStatusChanged(AnimationStatus status) {
+    // This can happen if an earlier status listener ends up calling dispose()
+    // on this object.
+    // TODO(abarth): Consider changing AnimationController not to call listeners
+    // that were removed while calling other listeners.
+    // See <https://github.com/flutter/flutter/issues/7533>.
+    if (controller == null)
+      return;
+
     if (status == AnimationStatus.dismissed) {
       navigator.pop();
       assert(controller == null);

packages/flutter/test/animation/iteration_patterns_test.dart

-// Copyright 2016 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 'package:flutter_test/flutter_test.dart';
-import 'package:flutter/animation.dart';
-import 'package:flutter/widgets.dart';
-
-void main() {
-  setUp(() {
-    WidgetsFlutterBinding.ensureInitialized();
-    WidgetsBinding.instance.resetEpoch();
-  });
-
-  test('AnimationController with mutating listener', () {
-    final AnimationController controller = new AnimationController(
-      duration: const Duration(milliseconds: 100),
-      vsync: const TestVSync(),
-    );
-    final List<String> log = <String>[];
-
-    final VoidCallback listener1 = () { log.add('listener1'); };
-    final VoidCallback listener3 = () { log.add('listener3'); };
-    final VoidCallback listener4 = () { log.add('listener4'); };
-    final VoidCallback listener2 = () {
-      log.add('listener2');
-      controller.removeListener(listener1);
-      controller.removeListener(listener3);
-      controller.addListener(listener4);
-    };
-
-    controller.addListener(listener1);
-    controller.addListener(listener2);
-    controller.addListener(listener3);
-    controller.value = 0.2;
-    expect(log, <String>['listener1', 'listener2']);
-    log.clear();
-
-    controller.value = 0.3;
-    expect(log, <String>['listener2', 'listener4']);
-    log.clear();
-
-    controller.value = 0.4;
-    expect(log, <String>['listener2', 'listener4']);
-    log.clear();
-  });
-
-  test('AnimationController with mutating status listener', () {
-    final AnimationController controller = new AnimationController(
-      duration: const Duration(milliseconds: 100),
-      vsync: const TestVSync(),
-    );
-    final List<String> log = <String>[];
-
-    final AnimationStatusListener listener1 = (AnimationStatus status) { log.add('listener1'); };
-    final AnimationStatusListener listener3 = (AnimationStatus status) { log.add('listener3'); };
-    final AnimationStatusListener listener4 = (AnimationStatus status) { log.add('listener4'); };
-    final AnimationStatusListener listener2 = (AnimationStatus status) {
-      log.add('listener2');
-      controller.removeStatusListener(listener1);
-      controller.removeStatusListener(listener3);
-      controller.addStatusListener(listener4);
-    };
-
-    controller.addStatusListener(listener1);
-    controller.addStatusListener(listener2);
-    controller.addStatusListener(listener3);
-    controller.forward();
-    expect(log, <String>['listener1', 'listener2']);
-    log.clear();
-
-    controller.reverse();
-    expect(log, <String>['listener2', 'listener4']);
-    log.clear();
-
-    controller.forward();
-    expect(log, <String>['listener2', 'listener4']);
-    log.clear();
-
-    controller.dispose();
-  });
-
-  testWidgets('AnimationController with throwing listener', (WidgetTester tester) async {
-    final AnimationController controller = new AnimationController(
-      duration: const Duration(milliseconds: 100),
-      vsync: const TestVSync(),
-    );
-    final List<String> log = <String>[];
-
-    final VoidCallback listener1 = () { log.add('listener1'); };
-    final VoidCallback badListener = () { log.add('badListener'); throw null; };
-    final VoidCallback listener2 = () { log.add('listener2'); };
-
-    controller.addListener(listener1);
-    controller.addListener(badListener);
-    controller.addListener(listener2);
-    controller.value = 0.2;
-    expect(log, <String>['listener1', 'badListener', 'listener2']);
-    expect(tester.takeException(), isNullThrownError);
-    log.clear();
-  });
-
-  testWidgets('AnimationController with throwing status listener', (WidgetTester tester) async {
-    final AnimationController controller = new AnimationController(
-      duration: const Duration(milliseconds: 100),
-      vsync: const TestVSync(),
-    );
-    final List<String> log = <String>[];
-
-    final AnimationStatusListener listener1 = (AnimationStatus status) { log.add('listener1'); };
-    final AnimationStatusListener badListener = (AnimationStatus status) { log.add('badListener'); throw null; };
-    final AnimationStatusListener listener2 = (AnimationStatus status) { log.add('listener2'); };
-
-    controller.addStatusListener(listener1);
-    controller.addStatusListener(badListener);
-    controller.addStatusListener(listener2);
-    controller.forward();
-    expect(log, <String>['listener1', 'badListener', 'listener2']);
-    expect(tester.takeException(), isNullThrownError);
-    log.clear();
-    controller.dispose();
-  });
-}

packages/flutter/test/foundation/change_notifier_test.dart

@@ -24,12 +24,12 @@ void main() {
     test.addListener(listener);
     test.addListener(listener);
     test.notify();
-    expect(log, <String>['listener']);
+    expect(log, <String>['listener', 'listener']);
     log.clear();
 
     test.removeListener(listener);
     test.notify();
-    expect(log, <String>[]);
+    expect(log, <String>['listener']);
     log.clear();
 
     test.removeListener(listener);
@@ -79,7 +79,7 @@ void main() {
     test.removeListener(listener2);
     test.addListener(listener2);
     test.notify();
-    expect(log, <String>['badListener', 'listener2']);
+    expect(log, <String>['badListener', 'listener1', 'listener2']);
     expect(tester.takeException(), isNullThrownError);
     log.clear();
   });
@@ -110,7 +110,7 @@ void main() {
     log.clear();
 
     test.notify();
-    expect(log, <String>['listener2', 'listener4']);
+    expect(log, <String>['listener2', 'listener4', 'listener4']);
     log.clear();
   });