AnimationController The named parameter 'vsync' isn't defined

AnimationController stopped working because somehow vsync is not a named parameter anymore.

This line of code stopped working.

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

It now shows an error saying:

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

I use this exact same code in two different apps, in one of them I just removed the fading text animation as a hot fix, but on the other app I need a real fix. Has anyone seen this problem recently?

Note:

-This exact same code has been working for months and stopped working after an update.

-The surrounding class does have: 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


[✓] Flutter (Channel master, 1.21.0-6.0.pre.140, on Mac OS X 10.15.5 19F101, locale en-MX)
    • Flutter version 1.21.0-6.0.pre.140 at /Users/luisharo/Developer/flutter
    • Framework revision 7884420a0a (25 hours ago), 2020-07-31 20:20:00 +0200
    • Engine revision 280bbfc763
    • Dart version 2.10.0 (build 2.10.0-2.0.dev bd528bfbd6)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/luisharo/Library/Android/sdk
    • Platform android-29, build-tools 29.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_212-release-1586-b4-5784211)
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    • Xcode 11.5, Build version 11E608c
    • CocoaPods version 1.8.4

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    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 45.1.1
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    • JKM LX3 (mobile)       • 7MLNW19723003608                     • android-arm64  • Android 9 (API 28)
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      (simulator)
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• No issues found!

Solution 1:

In your pubspec.yml

change this to:

environment:
  sdk: ">=2.8.0 <3.0.0"

and flutter pub get

in Android Studio invalidate the cache and restart, you should be good to go.

Credit : https://github.com/flutter/flutter/issues/62752#issuecomment-667744745

Solution 2:

What happened is that @required syntax was migrated during the rollout of null-safety to now just be required. This is valid new-Dart, but if you upgrade with your editor open, it will have stale build rules. Simply run flutter clean and restart your IDE, and that should do it.

Hopefully no need to restart your computer, change internet providers, etc.

Solution 3:

A few things (unfortunately not pinpointed) that help me with issues like this:

**edit: I would recommend doing these in order, hopefully the issue will be solved before you reach the end of the list.

• run flutter upgrade
• run flutter pub get
• run flutter clean
• restart IDE
• change flutter channel
• and in this case, change minimum SDK version from 2.7.0 to 2.8.0.

There are, of course, caveats to a few of these tactics. More experienced developers would surely have more details to offer, but I haven't encountered issues with this approach.