No dispose method to dispose the ScrollablePositionedList controller

[flutternoob]

Problem description

Steps to reproduce

I tried calling .dispose() on the itemController ItemScrollController, but could not find a dispose() method. If I switch between screens during a very slow scroll (for eg., 2 minutes), I get an error. I checked the API reference and could not find any information on how to dispose the controller. Is there a work around to disposing the controller?

Expected behavior

Expected the controller to dispose

Actual behavior

Error while changing between screens:

The following assertion was thrown while finalizing the widget tree:
_ScrollablePositionedListState#0854d(tickers: tracking 1 ticker) was disposed with an active Ticker.

_ScrollablePositionedListState created a Ticker via its TickerProviderStateMixin, but at the time dispose() was called on the mixin, that Ticker was still active. 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.

The offending ticker was: _WidgetTicker(created by _ScrollablePositionedListState#0854d(tickers: tracking 0 tickers))
The stack trace when the _WidgetTicker was actually created was:
#0      new Ticker.<anonymous closure> (package:flutter/src/scheduler/ticker.dart:67:40)
#1      new Ticker (package:flutter/src/scheduler/ticker.dart:69:6)
#2      new _WidgetTicker (package:flutter/src/widgets/ticker_provider.dart:271:81)
#3      TickerProviderStateMixin.createTicker (package:flutter/src/widgets/ticker_provider.dart:202:34)
#4      new AnimationController (package:flutter/src/animation/animation_controller.dart:247:21)
#5      _ScrollablePositionedListState._startScroll.<anonymous closure>.<anonymous closure> (package:scrollable_positioned_list/src/scrollable_positioned_list.dart:477:15)
#6      SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1144:15)
#7      SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1090:9)
#8      SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:998:5)
#12     _invoke (dart:ui/hooks.dart:161:10)
#13     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:253:5)
#14     _drawFrame (dart:ui/hooks.dart:120:31)
(elided 3 frames from dart:async)

When the exception was thrown, this was the stack: 
#0      TickerProviderStateMixin.dispose.<anonymous closure> (package:flutter/src/widgets/ticker_provider.dart:219:13)
#1      TickerProviderStateMixin.dispose (package:flutter/src/widgets/ticker_provider.dart:237:6)
#2      _ScrollablePositionedListState.dispose (package:scrollable_positioned_list/src/scrollable_positioned_list.dart:290:11)
#3      StatefulElement.unmount (package:flutter/src/widgets/framework.dart:4721:11)

Environment

[√] Flutter (Channel stable, 2.0.5, on Microsoft Windows [Version 10.0.19042.928], locale en-IN)
    • Flutter version 2.0.5 at c:\src\flutter
    • Framework revision adc687823a (2 weeks ago), 2021-04-16 09:40:20 -0700
    • Engine revision b09f014e96
    • Dart version 2.12.3

[√] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at C:\Users\Ankush\AppData\Local\Android\sdk
    • Platform android-30, build-tools 30.0.3
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.1.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code, 64-bit edition (version 1.54.1)
    • VS Code at C:\Program Files\Microsoft VS Code
    • Flutter extension version 3.21.0

[√] Connected device (3 available)
    • SM A205F (mobile) • RZ8M92CX7PJ • android-arm64  • Android 10 (API 29)
    • Chrome (web)      • chrome      • web-javascript • Google Chrome 90.0.4430.93
    • Edge (web)        • edge        • web-javascript • Microsoft Edge 90.0.818.51

• No issues found!

[ryanlath]

This is how I fixed it (for now)...
ryanlath@5eb46e1

The "mounted" part is because I don't have time to track down what else is not being stopped/canceled/disposed of properly...

oops... you might need add "late" if using null-safety:

late AnimationController controller;

[flutternoob]

@ryanlath Thanks for the link to the code. I am using null safety. Instead of using the "late" keyword, as an example, I do the following:

String? variableName;

[lff5]

Yes, i am experiencing exact same problem after putting the main ScrollablePosList view into PageView().
The view widget containing the SPL is with AutomaticKeepAliveClientMixin. Exception occurs when calling scrollTo() from the other view.

ryanlath@5eb46e1 fix works.

When will this (or something equivalent) be merged?

[lff5]

#262 is the same issue.