How to use 2 mixins in State in Flutter?

Question

I have a state class

class ListScreenState extends State<ListScreen>...

And I want to use AutomaticKeepAliveClientMixin (to prevent the TabBar that holds these screens from disposing of) and TickerProviderStateMixin because I have the animation controller that requires it. But when I put both mixins in this class there's an error:

error: Type parameters could not be inferred for the mixin 'TickerProviderStateMixin' because the base class implements the mixin's supertype constraint 'State<T>' in multiple conflicting ways (mixin_inference_inconsistent_matching_classes at [myapp] lib/trips/ListScreen.dart:21)

I couldn't really find a good explanation of how to use mixins in one class. Any help is appreciated.

Here's the full code:

import 'package:flutter/widgets.dart';    

class ListScreen extends StatefulWidget {

  @override
  State<StatefulWidget> createState() {
    return ListScreenState();
  }
}

 class ListScreenState extends State<ListScreen>
    with AutomaticKeepAliveClientMixin, TickerProviderStateMixin {

  AnimationController controller;

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

    controller = AnimationController(
        duration: const Duration(milliseconds: 250), vsync: this);

  }

  @override
  bool get wantKeepAlive => true;
}

Dart specifically complains about adding TickerProviderStateMixin. If I remove AutomaticKeepAliveClientMixin, then it doesn't complain anymore.

Please show the code that produces this error. – Günter Zöchbauer Oct 16 '18 at 07:11 — Günter Zöchbauer, Oct 16 '18 at 07:11

score 47 · Accepted Answer · answered Oct 16 '18 at 07:12

47

class ListScreenState extends State<ListScreen> with AutomaticKeepAliveClientMixin, TickerProviderStateMixin {
  // TODO: implement wantKeepAlive
  @override
  bool get wantKeepAlive => null;

}

answered Oct 16 '18 at 07:12

Günter Zöchbauer

623,577
216
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This works, only if I remove TickerProviderStateMixin – Dmitry Volkov Oct 16 '18 at 07:48
What do you mean with "works" or "does not work"? I added this code to my app and it didn't complain. – Günter Zöchbauer Oct 16 '18 at 07:49
Please also add the code of the `ListScreen` class declaration. – Günter Zöchbauer Oct 16 '18 at 07:49
It gives me an error: Type parameters could not be inferred for the mixin 'TickerProviderStateMixin' because the base class implements the mixin's supertype constraint 'State' in multiple conflicting ways (mixin_inference_inconsistent_matching_classes at [myapp] lib/trips/ListScreen.dart:21) – Dmitry Volkov Oct 16 '18 at 07:53
Is this error from the analyzer or do you get it only at runtime? What flutter version are you using? (`flutter --version`). – Günter Zöchbauer Oct 16 '18 at 07:54
It is from analyser. Version of flutter is: Flutter 0.8.2 • channel beta • https://github.com/flutter/flutter.git Framework • revision 5ab9e70727 (6 weeks ago) • 2018-09-07 12:33:05 -0700 Engine • revision 58a1894a1c Tools • Dart 2.1.0-dev.3.1.flutter-760a9690c2 – Dmitry Volkov Oct 16 '18 at 07:56
1

Can you try with `beta v0.9.4`? – Günter Zöchbauer Oct 16 '18 at 07:57
It worked with v0.9.4! I didn't even think of it, because tried it a month or two ago and it didn't work with older versions. Thank you! – Dmitry Volkov Oct 16 '18 at 08:01
Glad to hear! Was a since fixed Dart bug then. – Günter Zöchbauer Oct 16 '18 at 08:05

score 18 · Answer 2 · answered Feb 17 '20 at 15:29

18

For anyone coming here using SingleTickerProviderStateMixin, simply remove the Single from the name.

answered Feb 17 '20 at 15:29

Chris Jensen

485
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14

How to use 2 mixins in State in Flutter?

2 Answers2