认识lifecycle

用于系统组件的生命周期与普通组件之间的解耦。
具体表现为自定义组件不依赖页面（activity，fragment）生命周期的回调方法。
原理：通过对观察者模式，实现对页面生命周期的监听。观察者模式的两个类：LifecycleObserver和LifecycleOwner。
ComponentActivity实现了LifecycleOwner接口，通过LifecycleOwner的getLifecycle()方法来实现观察者模式。

public class ComponentActivity extends androidx.core.app.ComponentActivity implementsContextAware,LifecycleOwner,ViewModelStoreOwner,HasDefaultViewModelProviderFactory,SavedStateRegistryOwner,OnBackPressedDispatcherOwner,ActivityResultRegistryOwner,ActivityResultCaller {

使用LifeCycle

自定义组件MyMediaPlayer，功能为进入页面自动播放音频文件，退到后台停止播放，清楚后台应用程序释放MediaPlayer。

public class MyMediaPlayer implements DefaultLifecycleObserver {private MediaPlayer mediaPlayer;@Overridepublic void onCreate(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onCreate(owner);init();start("/storage/emulated/0/Android/data/cn.jn.mytest/files/a.mp3");Log.d("MyMediaPlayer", "onCreate");}@Overridepublic void onStop(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onStop(owner);mediaPlayer.stop();Log.d("MyMediaPlayer", "onStop");}@Overridepublic void onDestroy(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onDestroy(owner);Log.d("MyMediaPlayer", "onDestroy");mediaPlayer.release();}private void init() {mediaPlayer = new MediaPlayer();mediaPlayer.setOnPreparedListener(new MediaPlayer.OnPreparedListener() {@Overridepublic void onPrepared(MediaPlayer mp) {mediaPlayer.start();}});}private void start(String url) {try {mediaPlayer.setDataSource(url);mediaPlayer.prepareAsync();} catch (IOException e) {throw new RuntimeException(e);}}}

页面

public class MainActivity extends AppCompatActivity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);getLifecycle().addObserver(new MyMediaPlayer());}}

日志

---------------------------- PROCESS STARTED (20043) for package cn.jn.mytest ----------------------------
2023-04-08 15:14:59.915 20043-20043 MyMediaPlayer           cn.jn.mytest                         D  onCreate
2023-04-08 15:15:04.566 20043-20043 MyMediaPlayer           cn.jn.mytest                         D  onStop
2023-04-08 15:15:06.011 20043-20043 MyMediaPlayer           cn.jn.mytest                         D  onDestroy
---------------------------- PROCESS ENDED (20043) for package cn.jn.mytest ----------------------------

LifecycleService的使用

1. 添加依赖

    implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

2. 创建类，继承 LifecycleService类，声明MService 。

public class MService extends LifecycleService {

        <serviceandroid:name=".MService"android:exported="true" />

3. 实现观察者 DefaultLifecycleObserver

    static class MyObserver implements DefaultLifecycleObserver {@Overridepublic void onCreate(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onCreate(owner);Log.d("MService", "开启了服务");}@Overridepublic void onDestroy(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onDestroy(owner);Log.d("MService", "关闭了服务");}}

4. 绑定观察者

    public MService() {MainActivity.MyObserver myObserver = new MainActivity.MyObserver();getLifecycle().addObserver(myObserver);}

5. 查看效果
   开启服务

                Intent intent = new Intent(getApplicationContext(), MService.class);startService(intent);

关闭服务

                Intent intent = new Intent(getApplicationContext(), MService.class);stopService(intent);

日志

2023-04-08 16:32:44.552  7398-7398  MService                cn.jn.mytest                         D  开启了服务
2023-04-08 16:32:45.708  7398-7398  MService                cn.jn.mytest                         D  关闭了服务

ProcessLifecycleOwner

作用：监听这个应用的生命周期，可以判断当前应用是在前台还是在后台，或者从后台回到前台。

ProcessLifecycleOwner使用
ProcessLifecycleOwner要在Application中使用。onCreate的方法在整个应用生命周期中只会调用一次，onDestroy永远也不会调用。

    implementation 'androidx.lifecycle:lifecycle-extensions:2.2.0'

              ProcessLifecycleOwner.get().getLifecycle().addObserver(new DefaultLifecycleObserver() {@Overridepublic void onCreate(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onCreate(owner);Log.d("ProcessLifecycleOwner", "onCreate");}@Overridepublic void onStart(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onStart(owner);isForeground = true;Log.d("ProcessLifecycleOwner", "onStart");}@Overridepublic void onResume(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onResume(owner);Log.d("ProcessLifecycleOwner", "onResume");}@Overridepublic void onPause(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onPause(owner);Log.d("ProcessLifecycleOwner", "onPause");}@Overridepublic void onStop(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onStop(owner);isForeground = false;Log.d("ProcessLifecycleOwner", "onStop");}@Overridepublic void onDestroy(@NonNull LifecycleOwner owner) {DefaultLifecycleObserver.super.onDestroy(owner);Log.d("ProcessLifecycleOwner", "onDestroy");}});