Exception: DraggableScrollbar was disposed but didn't dispose all its Tickers

[diablodale]

I have a reproducible Exception which appears in my console, but doesn't crash the app. It suggests
_DraggableScrollbarState was disposed with an active Ticker. Specifically, that _DraggableScrollbarState created a Ticker via its TickerProviderStateMixin, but at the time dispose() was called on the mixin, that Ticker was still active.

The warning writes that all Tickers must be disposed before calling super.dispose(). Tickers used by AnimationControllers should be disposed by calling dispose() on the AnimationController itself. Otherwise, the ticker will leak.

Setup

Flutter 0.11.3 • channel beta
Framework • revision 72bf075e8d (6 days ago) • 2018-11-09 20:36:17 -0800
Engine • revision 5646e86a6f
Tools • Dart 2.1.0 (build 2.1.0-dev.9.3 9c07fb64c4)
Draggable Scrollbar 0.0.4

Repo

1. Create an app which has a Scaffold and two tabs within it. Within each tab is a DraggableScrollbar surrounding a ListView.
2. Populate the ListViews with data
3. Click on tab 1.
4. Click on tab 2.
5. Scroll quickly down so it has momentum and that the scroll tab remains visible
6. Quickly click to tab 1

Result

Exception written above and detailed below. You have to switch tabs quickly while scrolling is happening and the scroll tab is visible. If you click slowly, the exception warning does not appear.

Expected

No exception

Detail

I/flutter (15282): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter (15282): The following assertion was thrown while finalizing the widget tree:
I/flutter (15282): _DraggableScrollbarState#cc375(tickers: tracking 1 ticker) was disposed with an active Ticker.
I/flutter (15282): _DraggableScrollbarState created a Ticker via its TickerProviderStateMixin, but at the time
I/flutter (15282): dispose() was called on the mixin, that Ticker was still active. All Tickers must be disposed before
I/flutter (15282): calling super.dispose(). Tickers used by AnimationControllers should be disposed by calling
I/flutter (15282): dispose() on the AnimationController itself. Otherwise, the ticker will leak.
I/flutter (15282): The offending ticker was: _WidgetTicker(created by _DraggableScrollbarState#cc375(lifecycle state:
I/flutter (15282): created, tickers: tracking 1 ticker))
I/flutter (15282): The stack trace when the _WidgetTicker was actually created was:
I/flutter (15282): #0      new Ticker.<anonymous closure> (package:flutter/src/scheduler/ticker.dart:64:40)
I/flutter (15282): #1      new Ticker (package:flutter/src/scheduler/ticker.dart:66:6)
I/flutter (15282): #2      new _WidgetTicker (package:flutter/src/widgets/ticker_provider.dart:225:80)
I/flutter (15282): #3      __DraggableScrollbarState&State&TickerProviderStateMixin.createTicker (package:flutter/src/widgets/ticker_provider.dart:161:34)
I/flutter (15282): #4      new AnimationController (package:flutter/src/animation/animation_controller.dart:244:21)
I/flutter (15282): #5      _DraggableScrollbarState.initState (package:draggable_scrollbar/draggable_scrollbar.dart:340:33)
I/flutter (15282): #6      StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3808:58)
I/flutter (15282): #7      ComponentElement.mount (package:flutter/src/widgets/framework.dart:3674:5)
I/flutter (15282): #8      Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter (15282): #9      Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter (15282): #10     ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3710:16)
I/flutter (15282): #11     Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter (15282): #12     BuildOwner.buildScope (package:flutter/src/widgets/framework.dart:2286:33)
I/flutter (15282): #13     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:676:20)
I/flutter (15282): #14     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter (15282): #15     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (15282): #16     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (15282): #17     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter (15282): #18     _invoke (dart:ui/hooks.dart:151:13)
I/flutter (15282): #19     _drawFrame (dart:ui/hooks.dart:140:3)
I/flutter (15282):
I/flutter (15282): When the exception was thrown, this was the stack:
I/flutter (15282): #0      __DraggableScrollbarState&State&TickerProviderStateMixin.dispose.<anonymous closure> (package:flutter/src/widgets/ticker_provider.dart:178:13)
I/flutter (15282): #1      __DraggableScrollbarState&State&TickerProviderStateMixin.dispose (package:flutter/src/widgets/ticker_provider.dart:191:6)
I/flutter (15282): #2      _DraggableScrollbarState.dispose (package:draggable_scrollbar/draggable_scrollbar.dart:355:11)
I/flutter (15282): #3      StatefulElement.unmount (package:flutter/src/widgets/framework.dart:3878:12)
I/flutter (15282): #4      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1709:13)
I/flutter (15282): #5      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #6      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #7      _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #8      _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #9      ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #10     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #11     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #12     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #13     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #14     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #15     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #16     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #17     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #18     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #19     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #20     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #21     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #22     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #23     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #24     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4826:14)
I/flutter (15282): #25     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #26     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #27     SingleChildRenderObjectElement.visitChildren (package:flutter/src/widgets/framework.dart:4826:14)
I/flutter (15282): #28     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #29     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #30     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #31     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #32     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #33     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #34     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #35     _InactiveElements._unmount.<anonymous closure> (package:flutter/src/widgets/framework.dart:1707:7)
I/flutter (15282): #36     ComponentElement.visitChildren (package:flutter/src/widgets/framework.dart:3733:14)
I/flutter (15282): #37     _InactiveElements._unmount (package:flutter/src/widgets/framework.dart:1705:13)
I/flutter (15282): #38     ListIterable.forEach (dart:_internal/iterable.dart:39:13)
I/flutter (15282): #39     _InactiveElements._unmountAll (package:flutter/src/widgets/framework.dart:1718:25)
I/flutter (15282): #40     BuildOwner.finalizeTree.<anonymous closure> (package:flutter/src/widgets/framework.dart:2372:27)
I/flutter (15282): #41     BuildOwner.lockState (package:flutter/src/widgets/framework.dart:2204:15)
I/flutter (15282): #42     BuildOwner.finalizeTree (package:flutter/src/widgets/framework.dart:2371:7)
I/flutter (15282): #43     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding&WidgetsBinding.drawFrame (package:flutter/src/widgets/binding.dart:678:18)
I/flutter (15282): #44     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter (15282): #45     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter (15282): #46     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter (15282): #47     _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter (15282): #48     _invoke (dart:ui/hooks.dart:151:13)
I/flutter (15282): #49     _drawFrame (dart:ui/hooks.dart:140:3)
I/flutter (15282): ════════════════════════════════════════════════════════════════════════════════════════════════════

[diablodale]

As a guess... I see two AnimationControllers being created

_thumbAnimationController = AnimationController(...
_labelAnimationController = AnimationController(...

yet only one being disposed

_thumbAnimationController.dispose();