2-1、LifeCycle基本使用

原文链接

1、LifeCycle监听Activity生命周期

普通组件在使用过程中通常需要依赖于系统组件的生命周期，有时候，我们不得不在系统组件的生命周期回调方法中，主动去调用普通组件的方法，或者对其进行控制，因为普通组件无法获知系统组件生命周期事件。

传统写法 public class LocationActivity extends AppCompatActivity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_location); //在页面创建时 初始化定位管理信息 initLocation(); } @Override protected void onResume() { super.onResume(); ///在页面显示时 开始定位 startLocation(); } @Override protected void onDestroy() { super.onDestroy(); //在页面销毁时停止定位 stopLocation(); } } LifecycleObserver写法

继承LifecycleObserver

@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)：注解的该方法在Activity的onCreate方法后会被调用

@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)：注解的该方法在Activity的onResume方法后会被调用

@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)：注解的该方法在Activity的onDestroy方法前会被调用

MyLocationListener.java

package com.xinhe.testandroid; import android.util.Log; import androidx.lifecycle.Lifecycle; import androidx.lifecycle.LifecycleObserver; import androidx.lifecycle.OnLifecycleEvent; public class MyLocationListener implements LifecycleObserver { public static final String TAG = "Location"; /** * 使用注解，使得在create时调用 */ @OnLifecycleEvent(Lifecycle.Event.ON_CREATE) public void initLocation() { Log.d(TAG, "initLocation"); } /** * 使用注解，使得在resume时调用 */ @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) public void startLocation() { Log.d(TAG, "startLocation"); } /** * 使用注解，使得在destroy时调用 */ @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) public void stopLocation() { Log.d(TAG, "stopLocation"); } }

getLifecycle().addObserver(myLocationListener);

只需要在Activity中注册定位对象，就可以在定位对象中，接收到Activity生命周期的变化通知

MainActivity.java

package com.xinhe.testandroid; import androidx.appcompat.app.AppCompatActivity; import android.os.Bundle; import android.util.Log; public class MainActivity extends AppCompatActivity { private static final String TAG = "Location"; public MyLocationListener myLocationListener; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); //初始化定位对象 myLocationListener = new MyLocationListener(); getLifecycle().addObserver(myLocationListener); Log.d(TAG,"onCreate"); } @Override protected void onResume() { super.onResume(); Log.d(TAG,"onResume"); } @Override protected void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); } }

运行结果

onCreate之后会自动调用initLocation

onResume之后会自动调用startLocation

stopLocation方法会在onDestroy方法之前调用

Location: onCreate
Location: initLocation
Location: onResume
Location: startLocation
// 退出应用后
Location: stopLocation
Location: onDestroy

2、LifeCycle监听Fragment生命周期

和Activity基本一致

public class BlankFragment extends Fragment { private static final String TAG = "Fragment"; public MyLocationListener myLocationListener; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.d(TAG,"onCreate"); //初始化定位对象 myLocationListener = new MyLocationListener(); getLifecycle().addObserver(myLocationListener); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { return inflater.inflate(R.layout.fragment_blank, container, false); } @Override public void onResume() { super.onResume(); Log.d(TAG,"onResume"); } @Override public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); } } 3、LifeCycle监听Service生命周期

监听service的生命周期需要添加依赖

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

创建Service时，继承LifecycleService的MyService.java

public class MyService extends LifecycleService { private static final String TAG = "MyServiceObserver"; private MyServiceObserver myServiceObserver; public MyService(){ myServiceObserver = new MyServiceObserver(); getLifecycle().addObserver(myServiceObserver); } @Override public void onCreate() { super.onCreate(); Log.d(TAG,"onCreate"); } @Override public void onDestroy() { super.onDestroy(); Log.d(TAG,"onDestroy"); } }

MyServiceObserver.java

public class MyServiceObserver implements LifecycleObserver { private static final String TAG = "MyServiceObserver"; @OnLifecycleEvent(Lifecycle.Event.ON_CREATE) public void startService(){ Log.d(TAG,"在MyServiceObserver中监听到Service启动 "); } @OnLifecycleEvent(Lifecycle.Event.ON_STOP) public void stopService(){ Log.d(TAG,"在MyServiceObserver中监听到Service停止 "); } }