Flutter中如何检测应用从最近应用列表中被移除？

当你从最近应用列表移除Flutter应用时，AppLifecycleState.detached往往不会被触发——这是因为系统此时会直接终止应用进程，Flutter的生命周期回调没有机会执行。下面分平台给出可行的解决方案：

Android平台：监听onTaskRemoved #

Android在应用从最近列表被移除时，会触发Activity的onTaskRemoved方法，我们可以通过MethodChannel将这个事件传递给Flutter：

Flutter端代码修改 #

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
  late MethodChannel _channel;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    // 初始化MethodChannel
    _channel = MethodChannel('app_lifecycle_channel');
    _channel.setMethodCallHandler((call) async {
      if (call.method == 'onTaskRemoved') {
        // 这里处理应用从最近列表被移除的逻辑
        print('应用已从最近列表移除');
      }
    });
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);
    // 保留原有生命周期逻辑
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('My App')),
        body: const Center(child: Text('Hello, World!')),
      ),
    );
  }
}

Android原生代码修改 #

打开android/app/src/main/kotlin/[你的包名]/MainActivity.kt，重写onTaskRemoved方法：

import io.flutter.embedding.android.FlutterActivity
import io.flutter.embedding.engine.FlutterEngine
import io.flutter.plugin.common.MethodChannel

class MainActivity : FlutterActivity() {
    private val CHANNEL = "app_lifecycle_channel"

    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
        super.configureFlutterEngine(flutterEngine)
        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler { call, result ->
            // 处理Flutter端调用（如果需要）
        }
    }

    override fun onTaskRemoved(rootIntent: android.content.Intent?) {
        super.onTaskRemoved(rootIntent)
        // 通过MethodChannel通知Flutter
        MethodChannel(flutterEngine?.dartExecutor?.binaryMessenger, CHANNEL).invokeMethod("onTaskRemoved", null)
    }
}

iOS平台：监听applicationWillTerminate #

iOS在应用被终止时会调用applicationWillTerminate方法（注意：如果应用处于后台挂起状态，系统可能直接终止进程而不触发此方法，但从最近列表移除后若进程被立刻终止，该方法会执行）：

Flutter端代码修改 #

和Android端类似，使用MethodChannel监听：

// 同Android端的Flutter代码，修改MethodChannel回调逻辑
_channel.setMethodCallHandler((call) async {
  if (call.method == 'onAppTerminated') {
    print('应用已从最近列表移除并终止');
  }
});

iOS原生代码修改 #

打开ios/Runner/AppDelegate.swift，修改如下：

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
    private let CHANNEL = "app_lifecycle_channel"
    
    override func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
        let channel = FlutterMethodChannel(name: CHANNEL, binaryMessenger: controller.binaryMessenger)
        channel.setMethodCallHandler({ [weak self] (call: FlutterMethodCall, result: FlutterResult) -> Void in
            // 处理Flutter调用
        })
        GeneratedPluginRegistrant.register(with: self)
        return super.application(application, didFinishLaunchingWithOptions: launchOptions)
    }

    override func applicationWillTerminate(_ application: UIApplication) {
        super.applicationWillTerminate(application)
        let controller : FlutterViewController = window?.rootViewController as! FlutterViewController
        let channel = FlutterMethodChannel(name: CHANNEL, binaryMessenger: controller.binaryMessenger)
        channel.invokeMethod("onAppTerminated", arguments: nil)
    }
}

注意事项 #

• Android的onTaskRemoved会在应用从最近列表被移除时准确触发，不管应用是否在前台。
• iOS的applicationWillTerminate不一定能100%捕获所有从最近列表移除的场景，因为iOS可能会将应用挂起而不立刻终止，但对于进程被直接杀死的情况，该方法会执行。
• 所有在这些回调中执行的逻辑要尽量轻量化，因为进程即将终止，耗时操作可能无法完成。

内容的提问来源于stack exchange，提问作者Gowtham