How to "undispose" animation controller for reuse?

Question

I'm new to Flutter and having a bit of trouble with lifecycle methods and animation controllers.

When I press the bottom button it begins playing animation, when I press the circle in the center it stops the animation, and if I press the bottom button again I get the error:

AnimationController.stop() called after AnimationController.dispose() AnimationController methods should not be used after calling dispose. 'package:flutter/src/animation/animation_controller.dart': Failed assertion: line 767 pos 7: '_ticker != null'

I want the animation to begin playing again instead. Thanks for any advice!

import 'package:flutter/cupertino.dart';
import 'package:provider/provider.dart';
import 'package:flutter/material.dart';
import 'model/app_state_model.dart';
import 'dart:developer' as developer;
import 'package:flutter_spinkit/flutter_spinkit.dart';
class ProductListTab extends StatefulWidget {
  @override
  _ProductListTabState createState() => _ProductListTabState();
}
class _ProductListTabState extends State<ProductListTab>
    with SingleTickerProviderStateMixin {
  var _isActive = true;
  var _time = " ";
  var _resultBox;
  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      crossAxisAlignment: CrossAxisAlignment.stretch,
      children: [
        Expanded(
            flex: 3,
            child: Container(
              color: Colors.lightBlue,
              child: Padding(
                  padding: const EdgeInsets.all(30.0),
                  child: Align(
                    alignment: Alignment(0, .6),
                    child: Container(
                        width: 150,
                        height: 150,
                        child: OutlinedButton(
                            //elevation: 0.0,
                            style: OutlinedButton.styleFrom(
                                shape: CircleBorder(),
                                backgroundColor: Colors.blue),
                            onPressed: () {
                              setState(() {
                                _time = "999";
                              });
                            },
                            child: AnimatedSwitcher(
                              duration: Duration(seconds: 1),
                              child: ResultBox(time: _time),
                            ))),
                  )),
            )),
        Expanded(
          flex: 2,
          child: Padding(
            padding: const EdgeInsets.all(30),
            child: Row(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                CupertinoButton(
                  child: Text(_isActive ? 'Cancel' : 'Ready'),
                  onPressed: () {
                    setState(() {
                      _isActive = !_isActive;
                      _time = null;
                    });
                  },
                  color: Colors.amber,
                )
              ],
            ),
          ),
        )
      ],
    );
  }
}
class ResultBox extends StatefulWidget {
  final String time;
  const ResultBox({
    String this.time,
    Key key,
  }) : super(key: key);
  @override
  _ResultBoxState createState() => _ResultBoxState();
}
class _ResultBoxState extends State<ResultBox>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;
  void initState() {
    this._controller =
        AnimationController(vsync: this, duration: Duration(seconds: 1));
    super.initState();
    _controller.reset();
  }
  Widget build(BuildContext context) {
    var _resultRow;
    if (widget.time != null) {
      _resultRow = Row(mainAxisAlignment: MainAxisAlignment.center, children: [
        Text(
          widget.time,
          style: TextStyle(color: Colors.white, fontSize: 50),
        ),
        Text(
          "ms",
          style: TextStyle(color: Colors.white, fontSize: 20),
        ),
      ]);
    } else {
      _resultRow = SpinKitWave(color: Colors.white, controller: _controller);
    }
    return FittedBox(
      fit: BoxFit.fitWidth,
      child: _resultRow,
    );
  }
  Widget dispose() {
    this._controller.dispose();
  }
}

Solution

If you look at the SpinkitWave class you sent in the comments: https://github.com/jogboms/flutter_spinkit/blob/master/lib/src/wave.dart

You will see that the below is its initState method:

  @override
  void initState() {
    super.initState();
    _controller = (widget.controller ?? AnimationController(vsync: this, duration: widget.duration))..repeat();
  }

What this is doing is saying if the user has passed in an AnimationController in as a parameter, then use that AnimationController, if not create a new one and use the duration that the user has passed in. Therefore if all you need the AnimationController for is to control the SpinKitWave widget, then I would suggest you are better off just passing in the duration to it and letting it then manage the AnimationController internally. i.e create the widget using the below.

// As you no longer need to handle the state of the AnimationController you can 
// convert the ResultBox into a StatelessWidget
class ResultBox extends StatelessWidget {
  final String time;
  const ResultBox({
   this.time,
    Key key,
  }) : super(key: key);
  Widget build(BuildContext context) {
    var _resultRow;
    if (widget.time != null) {
      _resultRow = Row(mainAxisAlignment: MainAxisAlignment.center, children: [
        Text(
          widget.time,
          style: TextStyle(color: Colors.white, fontSize: 50),
        ),
        Text(
          "ms",
          style: TextStyle(color: Colors.white, fontSize: 20),
        ),
      ]);
    } else {
      // The controller argument has been removed here and the duration
      // argument added
      _resultRow = SpinKitWave(color: Colors.white, duration: const Duration(seconds: 1);
    }
    return FittedBox(
      fit: BoxFit.fitWidth,
      child: _resultRow,
    );
  }
}

Comments

[JayDev]

Can you add the code for SpinKitWave please? - Nowhere in your code above does it call AnimationController.stop(). I'm assuming its that component that is doing it. As a first note though your dispose method isn't the lifecycle dispose method as it has a return type of Widget. The lifecycle event has a return type of void

[Jonah Kornberg]

@JayDev It's not because of SpinKitWave, its because the whole _ResultBox is re-rendered when _time changes that the animation disappears. I suppose this probably is not good practice Edit: You might be right actually because there is no Stop called

[Jonah Kornberg]

The code for SpinKitWave can be found here: github.com/jogboms/flutter_spinkit/blob/master/lib/src/…

[JayDev]

AnimationControllers can be abit tricky. But in this use case I don't think you really need to use it, as if you let it the SpinKitWave widget will create and manage its own. I'll show you what I mean in an answer

[Jonah Kornberg]

Thank you so much for reading through it and helping :) I have it working now.