Stream.listen 在 web 上完全重启 Flutter 后幸存下来

Question

Stream.listen() 似乎可以在网络上完全重启，有时也可以在移动设备上幸存下来。 main.dart

import 'package:flutter/material.dart';
import 'package:web_socket_channel/web_socket_channel.dart';
import 'dart:convert';
import 'dart:math';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) => MaterialApp(home: MyHomePage());
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var test = 0;
  late int randomInt;
  var random = Random();
  var uri = Uri.parse('wss://ws-feed-public.sandbox.pro.coinbase.com');
  late WebSocketChannel channel;
  String request = json.encode({
    "type": "subscribe",
    "product_ids": ["BTC-USD"],
    "channels": ["heartbeat"],
  });

  @override
  void initState() {
    randomInt = random.nextInt(1000);
    channel = WebSocketChannel.connect(uri);
    channel.sink.add(request);
    channel.stream.listen((event) {
      print('$randomInt: $test');
      test = test + 1;
    });
    super.initState();
  }

  @override
  Widget build(BuildContext context) => Container();
}

pubspec.yaml

name: echowebsocket
description: A new Flutter project.

version: 1.0.0+1

environment:
  sdk: ">=2.12.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  web_socket_channel: ^2.1.0

dev_dependencies:
  flutter_test:
    sdk: flutter

flutter:
  uses-material-design: true

当我在 Flutter Web 中运行上述代码并进行热重启（android studio 中的绿色播放按钮）时，流 .listen() 函数在重启后仍然存在，两个监听函数仍在运行。 冷运行后的示例输出（Chrome 关闭）：

This application is not configured to build on the web.
To add web support to a project, run `flutter create .`.
Launching lib/main.dart on Chrome in debug mode...
Waiting for connection from debug service on Chrome...
This app is linked to the debug service: ws://127.0.0.1:56738/yLBcQjxMep4=/ws
Debug service listening on ws://127.0.0.1:56738/yLBcQjxMep4=/ws

???? Running with sound null safety ????
Debug service listening on ws://127.0.0.1:56738/yLBcQjxMep4=/ws
582: 0
582: 1
582: 2
582: 3
582: 4
582: 5
582: 6
582: 7
582: 8

然后在热重启之后：

Performing hot restart...
Waiting for connection from debug service on Chrome...
582: 30
Restarted application in 155ms.
876: 0
876: 1
582: 31
876: 2
582: 32
876: 3
582: 33
582: 34
876: 4
582: 35
876: 5
582: 36
876: 6
582: 37
876: 7
876: 8

如您所见，现在执行了两个监听函数。我的印象是，任何状态都不应该在热重启后幸存下来。我有时能够在模拟器上重新创建这个问题，但它似乎每次都在网络上工作。这是颤振医生的输出：

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.5.2, on macOS 11.6 20G165 darwin-x64, locale en)
[!] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    ✗ cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    ✗ Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/macos#android-setup for more details.
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 2020.3)
[✓] Connected device (1 available)

! Doctor found issues in 1 category.

Answer 1

您遇到的是内存/资源泄漏。完成后，您需要覆盖关闭WebSocketChannel。

@override
void dispose() {
  channel.sink.close();
  super.dispose();
}

更新 问题是由于热重启在 Chrome 上的工作方式。请在 GitHub 上查看 issue。