From ded49cda273bc31f94d7520bf89fb5f6241ff1d8 Mon Sep 17 00:00:00 2001
From: Dan Field <dfield@gmail.com>
Date: Wed, 23 Jan 2019 16:30:41 -0800
Subject: [PATCH] Assert when calling a method that tries to use the ticker
 unsafely after dispose (#26991)

---
 .../src/animation/animation_controller.dart   | 30 +++++++++++++++++++
 .../animation/animation_controller_test.dart  | 17 +++++++++++
 2 files changed, 47 insertions(+)

diff --git a/packages/flutter/lib/src/animation/animation_controller.dart b/packages/flutter/lib/src/animation/animation_controller.dart
index c564ed62ca..9623bdc9ca 100644
--- a/packages/flutter/lib/src/animation/animation_controller.dart
+++ b/packages/flutter/lib/src/animation/animation_controller.dart
@@ -436,6 +436,11 @@ class AnimationController extends Animation<double>
       }
       return true;
     }());
+    assert(
+      _ticker != null,
+      'AnimationController.forward() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     _direction = _AnimationDirection.forward;
     if (from != null)
       value = from;
@@ -464,6 +469,11 @@ class AnimationController extends Animation<double>
       }
       return true;
     }());
+    assert(
+      _ticker != null,
+      'AnimationController.reverse() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     _direction = _AnimationDirection.reverse;
     if (from != null)
       value = from;
@@ -483,6 +493,11 @@ class AnimationController extends Animation<double>
   /// animation, when `target` is reached, [status] is reported as
   /// [AnimationStatus.completed].
   TickerFuture animateTo(double target, { Duration duration, Curve curve = Curves.linear }) {
+    assert(
+      _ticker != null,
+      'AnimationController.animateTo() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     _direction = _AnimationDirection.forward;
     return _animateToInternal(target, duration: duration, curve: curve);
   }
@@ -500,6 +515,11 @@ class AnimationController extends Animation<double>
   /// animation, when `target` is reached, [status] is reported as
   /// [AnimationStatus.dismissed].
   TickerFuture animateBack(double target, { Duration duration, Curve curve = Curves.linear }) {
+    assert(
+      _ticker != null,
+      'AnimationController.animateBack() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     _direction = _AnimationDirection.reverse;
     return _animateToInternal(target, duration: duration, curve: curve);
   }
@@ -626,6 +646,11 @@ class AnimationController extends Animation<double>
   /// canceled, meaning the future never completes and its [TickerFuture.orCancel]
   /// derivative future completes with a [TickerCanceled] error.
   TickerFuture animateWith(Simulation simulation) {
+    assert(
+      _ticker != null,
+      'AnimationController.animateWith() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     stop();
     return _startSimulation(simulation);
   }
@@ -662,6 +687,11 @@ class AnimationController extends Animation<double>
   ///  * [forward], [reverse], [animateTo], [animateWith], [fling], and [repeat],
   ///    which restart the animation controller.
   void stop({ bool canceled = true }) {
+    assert(
+      _ticker != null,
+      'AnimationController.stop() called after AnimationController.dispose()\n'
+      'AnimationController methods should not be used after calling dispose.'
+    );
     _simulation = null;
     _lastElapsedDuration = null;
     _ticker.stop(canceled: canceled);
diff --git a/packages/flutter/test/animation/animation_controller_test.dart b/packages/flutter/test/animation/animation_controller_test.dart
index 271f71613e..a2a180783a 100644
--- a/packages/flutter/test/animation/animation_controller_test.dart
+++ b/packages/flutter/test/animation/animation_controller_test.dart
@@ -4,6 +4,7 @@
 
 import 'dart:ui' as ui;
 
+import 'package:flutter/physics.dart';
 import 'package:flutter/semantics.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/animation.dart';
@@ -658,4 +659,20 @@ void main() {
       debugSemanticsDisableAnimations = null;
     });
   });
+
+  test('AnimationController methods assert _ticker is not null', () {
+    final AnimationController controller = AnimationController(
+      vsync: const TestVSync(),
+    );
+
+    controller.dispose();
+
+    expect(() => controller.animateBack(0), throwsAssertionError);
+    expect(() => controller.animateTo(0), throwsAssertionError);
+    expect(() => controller.animateWith(GravitySimulation(0, 0, 0, 0)), throwsAssertionError);
+    expect(() => controller.stop(), throwsAssertionError);
+    expect(() => controller.forward(), throwsAssertionError);
+    expect(() => controller.reverse(), throwsAssertionError);
+
+  });
 }