AnimationController未定义命名参数“vsync”

Question

controller=AnimationController（Duration：Duration（seconds：3）,vsync：this）；

它现在显示了一个错误：

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完全相同的代码，在其中一个应用程序中，我只是删除了褪色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？

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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    • Dart version 2.10.0 (build 2.10.0-2.0.dev bd528bfbd6)

 
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    • Platform android-29, build-tools 29.0.3
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• No issues found!

Answer 1

在pubspec.yml中

将其更改为：

environment:
  sdk: ">=2.8.0 <3.0.0"

和flutter pub get