【Flutter】Flutter 应用生命周期 ( 前台状态 resumed | 后台状态 paused | 非活动状态 inactive | 组件分离状态 detached )_flutter resumed

一、Flutter 应用生命周期

---

应用生命周期 :

• resumed : 应用进入前台 ;
• paused : 应用进入后台 ;
• inactive : 应用进入非活动状态 ;
• detached : 应用在运行但与组件分离 ;

Flutter 应用生命周期状态枚举 : 该枚举中四个生命周期状态 , 源码注释中详细说明了每个状态的用法 ;

/// States that an application can be in.
///
/// The values below describe notifications from the operating system.
/// Applications should not expect to always receive all possible
/// notifications. For example, if the users pulls out the battery from the
/// device, no notification will be sent before the application is suddenly
/// terminated, along with the rest of the operating system.
///
/// See also:
///
///  * [WidgetsBindingObserver], for a mechanism to observe the lifecycle state
///    from the widgets layer.
enum AppLifecycleState {
  /// The application is visible and responding to user input.
  resumed,

  /// The application is in an inactive state and is not receiving user input.
  ///
  /// On iOS, this state corresponds to an app or the Flutter host view running
  /// in the foreground inactive state. Apps transition to this state when in
  /// a phone call, responding to a TouchID request, when entering the app
  /// switcher or the control center, or when the UIViewController hosting the
  /// Flutter app is transitioning.
  ///
  /// On Android, this corresponds to an app or the Flutter host view running
  /// in the foreground inactive state.  Apps transition to this state when
  /// another activity is focused, such as a split-screen app, a phone call,
  /// a picture-in-picture app, a system dialog, or another window.
  ///
  /// Apps in this state should assume that they may be [paused] at any time.
  inactive,

  /// The application is not currently visible to the user, not responding to
  /// user input, and running in the background.
  ///
  /// When the application is in this state, the engine will not call the
  /// [Window.onBeginFrame] and [Window.onDrawFrame] callbacks.
  paused,

  /// The application is still hosted on a flutter engine but is detached from
  /// any host views.
  ///
  /// When the application is in this state, the engine is running without
  /// a view. It can either be in the progress of attaching a view when engine
  /// was first initializes, or after the view being destroyed due to a Navigator
  /// pop.
  detached,
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48

二、监听 Flutter 应用生命周期

---

监听 Flutter 应用生命周期 , 需要在页面 StatefulWidget 的 initState 页面生命周期函数中注册 WidgetsBindingObserver 观察者 ;

  @override
  void initState() {
    super.initState();
    /// 如果想要监听应用生命周期 , 要先绑定观察者 ,
    /// 绑定完成后 , 如果应用生命周期发生了变化 ,
    /// 就会回调 didChangeAppLifecycleState 方法 ;
    WidgetsBinding.instance.addObserver(this);
  }
1
2
3
4
5
6
7
8

注册了 WidgetsBindingObserver 观察者之后 , 在应用生命周期改变时 , 就会回调 WidgetsBindingObserver 类的 didChangeAppLifecycleState 方法 , 其 AppLifecycleState state 参数就是当前的应用生命周期状态 ;

  /// 当应用生命周期发生变化时 , 会回调该方法
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);

    print("当前的应用生命周期状态 : ${state}");

    if(state == AppLifecycleState.paused){
      print("应用进入后台 paused");

    }else if(state == AppLifecycleState.resumed){
      print("应用进入前台 resumed");

    }else if(state == AppLifecycleState.inactive){
      // 应用进入非活动状态 , 如来了个电话 , 电话应用进入前台
      // 本应用进入该状态
      print("应用进入非活动状态 inactive");

    }else if(state == AppLifecycleState.detached){
      // 应用程序仍然在 Flutter 引擎上运行 , 但是与宿主 View 组件分离
      print("应用进入 detached 状态 detached");

    }
  }
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

在 StatefulWidget 页面销毁时需要移除该 WidgetsBindingObserver 观察者 ;

  /// 移出组件中注册的观察者
  @override
  void dispose() {
    super.dispose();
    WidgetsBinding.instance.removeObserver(this);
  }
1
2
3
4
5
6

三、完整代码示例

---

完整代码示例 :

import 'package:flutter/material.dart';

class AppLifeCyclePage extends StatefulWidget {
  @override
  _AppLifeCyclePageState createState() => _AppLifeCyclePageState();
}

class _AppLifeCyclePageState extends State<AppLifeCyclePage> with WidgetsBindingObserver {

  @override
  void initState() {
    super.initState();
    /// 如果想要监听应用生命周期 , 要先绑定观察者 ,
    /// 绑定完成后 , 如果应用生命周期发生了变化 ,
    /// 就会回调 didChangeAppLifecycleState 方法 ;
    WidgetsBinding.instance.addObserver(this);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        // 标题
        title: Text("应用生命周期"),

        // 返回按钮
        leading: BackButton(),
      ),

      body: Container(
        // 居中设置
        alignment: Alignment.center,

        child: Text("应用生命周期"),
      ),
    );
  }

  /// 移出组件中注册的观察者
  @override
  void dispose() {
    super.dispose();
    WidgetsBinding.instance.removeObserver(this);
  }

  /// 当应用生命周期发生变化时 , 会回调该方法
  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    super.didChangeAppLifecycleState(state);

    print("当前的应用生命周期状态 : ${state}");

    if(state == AppLifecycleState.paused){
      print("应用进入后台 paused");

    }else if(state == AppLifecycleState.resumed){
      print("应用进入前台 resumed");

    }else if(state == AppLifecycleState.inactive){
      // 应用进入非活动状态 , 如来了个电话 , 电话应用进入前台
      // 本应用进入该状态
      print("应用进入非活动状态 inactive");

    }else if(state == AppLifecycleState.detached){
      // 应用程序仍然在 Flutter 引擎上运行 , 但是与宿主 View 组件分离
      print("应用进入 detached 状态 detached");

    }
  }
}

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72

运行效果 :

进入界面 : 进入界面后 , 由于还没有注册 WidgetsBindingObserver , 因此不打印日志 , 等界面加载完毕后 , 进行各种操作 ( 如按下 Home 键 , 按下回退键 , 按下菜单键 ) 时才打印日志 ;

按下菜单键 :

• 界面状态 :

• 打印日志 :

I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.inactive
I/flutter (30370): 应用进入非活动状态 inactive
D/FlutterView(30370): Detaching from a FlutterEngine: io.flutter.embedding.engine.FlutterEngine@9d12774
I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.paused
I/flutter (30370): 应用进入后台 paused
1
2
3
4
5

再次点击回到应用界面 :

• 界面状态 :

• 打印日志 :

I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.resumed
I/flutter (30370): 应用进入前台 resumed
D/FlutterView(30370): Attaching to a FlutterEngine: io.flutter.embedding.engine.FlutterEngine@9d12774
1
2
3

完整日志 :

# 按下菜单键
I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.inactive
I/flutter (30370): 应用进入非活动状态 inactive
D/FlutterView(30370): Detaching from a FlutterEngine: io.flutter.embedding.engine.FlutterEngine@9d12774
I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.paused
I/flutter (30370): 应用进入后台 paused

# 返回界面
I/flutter (30370): 当前的应用生命周期状态 : AppLifecycleState.resumed
I/flutter (30370): 应用进入前台 resumed
D/FlutterView(30370): Attaching to a FlutterEngine: io.flutter.embedding.engine.FlutterEngine@9d12774
1
2
3
4
5
6
7
8
9
10
11

四、相关资源

---

参考资料 :

• Flutter 官网 : https://flutter.dev/
• Flutter 插件下载地址 : https://pub.dev/packages
• Flutter 开发文档 : https://flutter.cn/docs ( 强烈推荐 )
• 官方 GitHub 地址 : https://github.com/flutter
• Flutter 中文社区 : https://flutter.cn/
• Flutter 实用教程 : https://flutter.cn/docs/cookbook
• Flutter CodeLab : https://codelabs.flutter-io.cn/
• Dart 中文文档 : https://dart.cn/
• Dart 开发者官网 : https://api.dart.dev/
• Flutter 中文网 ( 非官方 , 翻译的很好 ) : https://flutterchina.club/ , http://flutter.axuer.com/docs/
• Flutter 相关问题 : https://flutterchina.club/faq/ ( 入门阶段推荐看一遍 )

博客源码下载 :

• GitHub 地址 : https://github.com/han1202012/flutter_cmd ( 随博客进度一直更新 , 有可能没有本博客的源码 )

• 博客源码快照 : https://download.csdn.net/download/han1202012/15547438 ( 本篇博客的源码快照 , 可以找到本博客的源码 )