Flutter 封装：最佳实践 —— AppLifecycleState 状态监听封装

备注：Flutter v3.13 版本以下推荐使用；以上使用官方实现 AppLifecycleListener；

一、需求来源

项目中多页面需要同时监听 AppLifecycleState 根据状态实现不同的业务逻辑；尝试多种实现，使用起来比较麻烦，为了开发效率，随封装一个。代码不复杂，核心在于极简的封装方法。

效果如下：

//进入后台
[log] 2024-01-21 09:44:59.923812 MyHomePage onInactive
[log] 2024-01-21 09:44:59.926700 AppLifecycleStateObserverDemo onInactive
[log] 2024-01-21 09:45:00.906268 MyHomePage onHidden
[log] 2024-01-21 09:45:00.906750 AppLifecycleStateObserverDemo onHidden
[log] 2024-01-21 09:45:00.907225 MyHomePage onPause
[log] 2024-01-21 09:45:00.907635 AppLifecycleStateObserverDemo onPause

//进入前台
[log] 2024-01-21 09:45:12.167072 MyHomePage onHidden
[log] 2024-01-21 09:45:12.167362 AppLifecycleStateObserverDemo onHidden
[log] 2024-01-21 09:45:12.167607 MyHomePage onInactive
[log] 2024-01-21 09:45:12.167819 AppLifecycleStateObserverDemo onInactive
[log] 2024-01-21 09:45:13.071467 MyHomePage onResume
[log] 2024-01-21 09:45:13.072509 AppLifecycleStateObserverDemo onResume

// MyHomePage 为主页面；
// AppLifecycleStateObserverDemo 为特定业务界面；

二、使用示例

import 'package:flutter/material.dart';
import 'package:flutter_templet_project/util/AppLifecycleObserver.dart';
import 'package:flutter_templet_project/util/debug_log.dart';

class AppLifecycleStateObserverDemo extends StatefulWidget {

  AppLifecycleStateObserverDemo({
    super.key, 
    this.title
  });

  final String? title;

  @override
  State<AppLifecycleStateObserverDemo> createState() => _AppLifecycleStateObserverDemoState();
}

class _AppLifecycleStateObserverDemoState extends State<AppLifecycleStateObserverDemo> with
    AppLifecycleObserverMixin {

  final _scrollController = ScrollController();


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title ?? "$widget"),
        actions: ['done',].map((e) => TextButton(
          child: Text(e,
            style: TextStyle(color: Colors.white),
          ),
          onPressed: () => debugPrint(e),)
        ).toList(),
      ),
      body: buildBody(),
    );
  }

  buildBody() {
    return Scrollbar(
      controller: _scrollController,
      child: SingleChildScrollView(
        controller: _scrollController,
        child: Column(
          children: [
            Text("$widget"),
          ],
        ),
      ),
    );
  }

  /*************** AppLifecycleObserverMixin ***************/
  
  @override
  Future<void> onResume() async {
    // TODO: implement onResume
    DDLog("$widget onResume");
  }

  @override
  Future<void> onInactive() async {
    // TODO: implement onInactive
    DDLog("$widget onInactive");
  }

  @override
  Future<void> onPause() async {
    // TODO: implement onPause
    DDLog("$widget onPause");
  }

  @override
  Future<void> onDetached() async {
    // TODO: implement onDetached
    DDLog("$widget onDetached");
  }
  
  @override
  Future<void> onHidden() async {
    // TODO: implement onHidden
    ddLog("$widget onHidden");
  }
}

三、源码

1、AppLifecycleObserver 源码

/// app 前后台生命周期函数监听
class AppLifecycleObserver extends WidgetsBindingObserver{

  AppLifecycleObserver({
    required this.onResume,
    required this.onInactive,
    required this.onPause,
    required this.onDetached,
    required this.onHidden,
    this.data,
  });

  final AsyncCallback onResume;
  final AsyncCallback onInactive;
  final AsyncCallback onPause;
  final AsyncCallback onDetached;
  final AsyncCallback onHidden;
  final dynamic data;

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // DDLog('${Get.currentRoute} APP状态监听：$state, ${data ?? ""}');

    switch (state) {
      case AppLifecycleState.resumed:
        onResume();
        break;
      case AppLifecycleState.inactive:
        onInactive();
        break;
      case AppLifecycleState.paused:
        onPause();
        break;
      case AppLifecycleState.detached:
        onDetached();
        break;
     case AppLifecycleState.hidden:
       onHidden();
        break;
    }
  }
}

2、AppLifecycleObserverMixin 源码

/// app 前后台生命周期函数混入封装
mixin AppLifecycleObserverMixin<T extends StatefulWidget> on State<T>{
  late final _lifecycleEvent = AppLifecycleObserver(
    onResume: onResume,
    onInactive: onInactive,
    onPause: onPause,
    onDetached: onDetached,
  );

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(_lifecycleEvent);
  }

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

  Future<void> onResume() async {
    throw UnimplementedError("❌: $this 未实现 onResume");
  }

  Future<void> onInactive() async {
    throw UnimplementedError("❌: $this 未实现 onInactive");
  }

  Future<void> onPause() async {
    throw UnimplementedError("❌: $this 未实现 onPause");
  }

  Future<void> onDetached() async {
    throw UnimplementedError("❌: $this 未实现 onDetached");
  }
  
  Future<void> onHidden() async {
   throw UnimplementedError("❌: $this 未实现 onHidden");
  }

}

四、总结

1、Flutter 3.13 之后官方实现了一个 AppLifecycleListener

使用效果和 AppLifecycleObserverMixin 相同，基于官方优先原则（未来维护性考虑），建议大家使用官方 AppLifecycleListener实现功能。

class AppLifecycleListener with WidgetsBindingObserver, Diagnosticable {
  /// Creates an [AppLifecycleListener].
  AppLifecycleListener({
    WidgetsBinding? binding,
    this.onResume,
    this.onInactive,
    this.onHide,
    this.onShow,
    this.onPause,
    this.onRestart,
    this.onDetach,
    this.onExitRequested,
    this.onStateChange,
  })  : binding = binding ?? WidgetsBinding.instance,
        _lifecycleState = (binding ?? WidgetsBinding.instance).lifecycleState {
    this.binding.addObserver(this);
  }
  。。。

2、AppLifecycleObserverMixin 生命周期方法是一组，即使不使用也要全部实现（基于维护性考虑）；如果未实现会日志报错，提示到具体页面；

3、v3.13 以下使用请删除 onHidden 相关代码；

github