[移动开发]Flutter 动画监听未取消注册导致的异常记录

异常信息

背景：在弹窗上，含有一个动画控件，并且使用动回掉实现一些处理。当关闭弹窗时出现如下异常：

flutter exception detail-‘package:flutter/src/widgets/framework.dart’: Failed assertion: line 4109 pos 12: ‘_lifecycleState != _ElementLifecycle.defunct’: is not true.
W/flutter exception detail(28505): ‘package:flutter/src/widgets/framework.dart’: Failed assertion: line 4109 pos 12: ‘_lifecycleState != _ElementLifecycle.defunct’: is not true.
I/flutter (28505): flutter exception detail-dart:core-patch/errors_patch.dart 46:39 in _AssertionError._doThrowNew
I/flutter (28505): flutter exception detail-dart:core-patch/errors_patch.dart 36:5 in _AssertionError._throwNew
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 4109:12 in Element.markNeedsBuild
W/flutter exception detail(28505): dart:core-patch/errors_patch.dart 46:39 in _AssertionError._doThrowNew
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 1287:15 in State.setState
I/flutter (28505): flutter exception ************box_dialog.dart 128:7 in _MysteryBoxState._animListener
I/flutter (28505): flutter exception detail-package:flutter/src/animation/listener_helpers.dart 136:19 in AnimationLocalListenersMixin.notifyListeners
W/flutter exception detail(28505): dart:core-patch/errors_patch.dart 36:5 in _AssertionError._throwNew
I/flutter (28505): flutter exception detail-package:svgaplayer_flutter/player.dart 65:10 in SVGAAnimationController.clear
I/flutter (28505): flutter exception detail-package:svgaplayer_flutter/player.dart 47:5 in SVGAAnimationController.videoItem=
I/flutter (28505): flutter exception detail-package:svgaplayer_flutter/player.dart 77:5 in SVGAAnimationController.dispose
W/flutter exception detail(28505): package:flutter/src/widgets/framework.dart 4109:12 in Element.markNeedsBuild
I/flutter (28505): flutter exception ************box_dialog.dart 145:22 in _MysteryBoxState.dispose
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 4721:11 in StatefulElement.unmount
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2022:13 in _InactiveElements._unmount
W/flutter exception detail(28505): package:flutter/src/widgets/framework.dart 1287:15 in State.setState
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2020:7 in _InactiveElements._unmount.
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 4549:14 in ComponentElement.visitChildren
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2018:13 in _InactiveElements._unmount
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2020:7 in _InactiveElements._unmount.
W/flutter exception detail(28505): *********box_dialog.dart 128:7 in _MysteryBoxState._animListener
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 5961:14 in SingleChildRenderObjectElement.visitChildren
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2018:13 in _InactiveElements._unmount
W/flutter exception detail(28505): package:flutter/src/animation/listener_helpers.dart 136:19 in AnimationLocalListenersMixin.notifyListeners
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2020:7 in _InactiveElements._unmount.
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 4549:14 in ComponentElement.visitChildren
I/flutter (28505): flutter exception detail-package:flutter/src/widgets/framework.dart 2018:13 in _InactiveElements._unmount
W/flutter exception detail(28505): package:svgaplayer_flutter/player.dart 65:10 in SVGAAnimationController.clear

动画的实现方案

@override
  void initState() {
    super.initState();
    this._svgaController = SVGAAnimationController(vsync: this);
    loadAnimation();
  }
  
  void loadAnimation() async {
    this._svgaController.addListener(() { //TODO });
    this._svgaController.addStatusListener((status) {//TODO });
  }
@override
  void dispose() {
    _svgaController?.dispose();
    super.dispose();
  }

解决方案

 @override
  void initState() {
    super.initState();
    this._svgaController = SVGAAnimationController(vsync: this);
    loadAnimation();
  }
  
void loadAnimation() async {
    this._svgaController.addListener(_animListener);
    this._svgaController.addStatusListener(_animStatusListener);
  }
void _animListener() {
    //TODO
  }
  void _animStatusListener(AnimationStatus status) {
   //TODO
  }

@override
  void dispose() {
    _svgaController?.removeListener(_animListener);
    _svgaController?.removeStatusListener(_animStatusListener);
    _svgaController?.dispose();
    super.dispose();
  }