flutter - AnimationController 命名参数 'vsync' 未定义

Question

AnimationController 停止工作，因为不知何故 vsync 不再是命名参数。
这行代码停止工作。controller = AnimationController(duration: Duration(seconds: 3), vsync: this);它现在显示一个错误说:

The named parameter 'vsync' isn't defined.
Try correcting the name to an existing named parameter's name, or defining a named parameter with the name 'vsync'.dartundefined_named_parameter

我在两个不同的应用程序中使用了这个完全相同的代码，在其中一个应用程序中我只是删除了淡入淡出的文本动画作为热修复，但在另一个应用程序中我需要一个真正的修复。最近有人看到这个问题吗？
注意:
- 这个完全相同的代码已经工作了几个月，但在更新后停止工作。
-周边类(class)确实有: with TickerProviderStateMixin

class FadingText extends StatefulWidget {
  final String text;
  final int seconds;
  final TextStyle style;

  FadingText({this.text, this.seconds, this.style});

  @override
  _FadingTextState createState() => _FadingTextState();
}

class _FadingTextState extends State<FadingText> with TickerProviderStateMixin {
  AnimationController controller;
  Animation animation;

  @override
  Widget build(BuildContext context) {
    return Container(
      child: FadeTransition(
        opacity: animation,
        child: Text(widget.text, style: widget.style,),
      ),
    );
  }

  @override
  void initState() {
    super.initState();

    controller = AnimationController(duration: Duration(seconds: widget.seconds), vsync: this);
    animation = Tween(begin: 0.5, end: 1.0).animate(controller);

    animation.addStatusListener((status) {
      if (status == AnimationStatus.completed) { controller.reverse(); }
      else if (status == AnimationStatus.dismissed) { controller.forward(); }
    });

    controller.forward();
  }


  @override
  void dispose() {
    controller.dispose();
    super.dispose();
  }

}

Flutter Doctor


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• No issues found!

Answer 1

在您的 pubspec.yml将此更改为:

environment:
  sdk: ">=2.8.0 <3.0.0"

和 flutter pub get在android studio中然后使缓存无效并重新启动，你应该很高兴!
信用: https://github.com/flutter/flutter/issues/62752#issuecomment-667744745