检查 Stateless 小部件是否在 flutter 中被处理

Question

When my stateless widget built I play some sounds in sequence order by using this code:

await _audioPlayer.play(contentPath1, isLocal: true);
await Future.delayed(Duration(seconds: 4));
await _audioPlayer.play(contentPath2, isLocal: true);
await Future.delayed(Duration(seconds: 4));
await _audioPlayer.play(contentPath3, isLocal: true);

when the user closes the current widget before finish playing the sounds, The sounds still work even after closing the current route by using this code:

Navigator.pop(context);

my workaround is to use a boolean variable to indicate if the closing action has done.

Playing sound code:

await _audioPlayer.play(contentPath1, isLocal: true);
if (closed) return;
await Future.delayed(Duration(seconds: 4));
if (closed) return;
await _audioPlayer.play(contentPath2, isLocal: true);
if (closed) return;
await Future.delayed(Duration(seconds: 4));
if (closed) return;
await _audioPlayer.play(contentPath3, isLocal: true);

Closing the current widget:

closed = true;
_audioPlayer.stop();

Are there a better way to stop the async methods if my widget closed?

Answer 1

If you change your widget to a StatefulWidget then you can have a function like the following:

void _playSounds() {
  await _audioPlayer.play(contentPath1, isLocal: true);
  await Future.delayed(Duration(seconds: 4));
  if (!mounted) return;

  await _audioPlayer.play(contentPath2, isLocal: true);
  await Future.delayed(Duration(seconds: 4));
  if (!mounted) return;

  await _audioPlayer.play(contentPath3, isLocal: true);
}

and then in the dispose method just dispose of the player:

@override
void dispose() {
  _audioPlayer?.dispose();
  super.dispose();
}

Answer 2

The mounted getter is currently merged in master channel but it still not available in the stable channel.

https://github.com/flutter/flutter/pull/111619

In the mean time, we have 2 option

1. Use Stateful Widget directly (as accepted answer)
2. Implement a Stateful Widget wrapper with builder method to pass down the mounted getter also in a wrapper.

Wrapper widget

import 'package:flutter/material.dart';

class PrimitiveWrapper<T> {
  T value;

  PrimitiveWrapper(this.value);
}

class MountedWrapper extends StatefulWidget {
  final Widget Function(BuildContext context, PrimitiveWrapper<bool> mounted) builder;

  const MountedWrapper({
    required this.builder,
    super.key,
  });

  @override
  State<MountedWrapper> createState() => _MountedWrapperState();
}

class _MountedWrapperState extends State<MountedWrapper> {
  @override
  Widget build(BuildContext context) {
    return widget.builder.call(context, PrimitiveWrapper(mounted));
  }
}

Usage

class SubmitBtn extends StatelessWidget {

  ...

  Future<void> onSubmit(WidgetRef ref, BuildContext context, PrimitiveWrapper<bool> mounted) async {
    ...

    await topicRepo.add(topic);

    if (!mounted.value) {
      return;
    }

    ScaffoldMessenger.of(context).showSnackBar(
      const SnackBar(
        content: Text('Created topic'),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return MountedWrapper(
      builder: (context, mounted) {
        return Consumer(
          builder: (context, ref, child) {
            return ElevatedButton(
              onPressed: () {
                onSubmit(ref, context, mounted);
              },
              child: const Text('Create'),
            );
          },
        );
      },
    );
  }
}