Jetpack架构组件_LifeCycle组件

1.LifeCycle组件 

        LifeCycle组件可以让我们自定义的类能主动感知到Activity、Fragment、Application、Service等系统组件的生命周期。

       我们以百度定位为例，我们一般在Activity生命周期的onCreate回调函数里调用自定义类LocationService的Start()方法，在onStop回调里调用LocationService的stop()方法来启动和停止定位服务。

        利用LifeCycle让LocationService作为观察者，能感知到Activity的生命周期，当activity执行到onCreate与onStop时，LocationService自动调用它内部的start()与stop()方法来启动与停止定位，而无需再在activity里写调用LocationService.start()与LocationService.stop的代码了。当然这里的被观察者自然就是activty了。

2.使用LifeCycle解耦Activity与自定义组件 

2.1关键步骤 

     step1.自定义类（自定义组件）：

        （1）让自定义类（或者称作自定义组件）实现LifecycleObserver。 

        （2）在要执行的函数start()和stop()上面添加注解@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)与@OnLifecycleEvent(Lifecycle.Event.ON_STOP）。

2.2示例代码： 

        自定义类LocationService.java

package com.gaoting.lifecycleactivity;import android.util.Log;import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;/*** 封装了定位的开启和停止*/
public class LocationService implements LifecycleObserver {String TAG = "LocationService";/*** 开始定位*/@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)public void start() {Log.i(TAG, "开始定位");}/*** 停止定位*/@OnLifecycleEvent(Lifecycle.Event.ON_STOP)public void stop() {Log.i(TAG, "停止定位");}
}

        MainActivity.java

package com.gaoting.lifecycleactivity;import android.os.Bundle;import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;public class MainActivity extends AppCompatActivity {LocationService mLocationService;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mLocationService = new LocationService();getLifecycle().addObserver(mLocationService);}
}

3.使用LifeCycle解耦Service与自定义组件

3.1关键步骤 

         添加依赖：

        implementation libs.lifecycle.extensions

        step1:Service处理

        （1）让Service继承于LifecycleService

        （2）getLifecycle().addObserve()将观察者与被观察者绑定，即将自定义类与Service绑定。

        step2:自定义类的处理

        （1）实现LifecycleObserver接口。

        （2）添加标签注解事件，感知Service的生命周期。

3.2示例代码

实现Service类MyService.java。

package com.gaoting.lifecycleactivity;import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;import androidx.annotation.Nullable;
import androidx.lifecycle.LifecycleService;public class MyService extends LifecycleService {String TAG = "MyService";LocationService mlocationService;public MyService() {mlocationService = new LocationService();getLifecycle().addObserver(mlocationService);}@Overridepublic void onCreate() {Log.i(TAG, "onCreate");super.onCreate();}@Overridepublic int onStartCommand(@Nullable Intent intent, int flags, int startId) {Log.i(TAG, "onStartCommand");return super.onStartCommand(intent, flags, startId);}@Overridepublic void onDestroy() {Log.i(TAG, "onDestroy");super.onDestroy();}}

自定义类LocationService.java。

package com.gaoting.lifecycleactivity;import android.util.Log;import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;/*** 封装了定位的开启和停止*/
public class LocationService implements LifecycleObserver {String TAG = "LocationService";/*** 开始定位*/@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)public void start() {Log.i(TAG, "ON_CREATE开始定位");}/*** 停止定位*/@OnLifecycleEvent(Lifecycle.Event.ON_STOP)public void stop() {Log.i(TAG, "ON_STOP停止定位");}/*** 停止定位:用于感知Service的onDestroy生命周期*/@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)public void stopLoc() {Log.i(TAG, "ON_DESTROY停止定位");}
}

MainActivity类。

package com.gaoting.lifecycleactivity;import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;import androidx.activity.EdgeToEdge;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.graphics.Insets;
import androidx.core.view.ViewCompat;
import androidx.core.view.WindowInsetsCompat;
import androidx.databinding.DataBindingUtil;import com.gaoting.lifecycleactivity.databinding.ActivityMainBinding;public class MainActivity extends AppCompatActivity {String TAG = "MainActivity";ActivityMainBinding activityMainBinding;LocationService mLocationService;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_main);mLocationService = new LocationService();getLifecycle().addObserver(mLocationService);/*** 启动服务*/activityMainBinding.btStartService.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent i = new Intent(MainActivity.this, MyService.class);startService(i);}});/*** 停止服务*/activityMainBinding.btStopService.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Intent i = new Intent(MainActivity.this, MyService.class);stopService(i);}});}@Overrideprotected void onStop() {Log.i(TAG, "onStop");super.onStop();}@Overrideprotected void onDestroy() {Log.i(TAG, "onDestroy");super.onDestroy();}
}

4.使用ProcessLifecycleOwner感知Application。

4.1关键步骤

        添加依赖：implementation libs.lifecycle.extensions。

        step1：MyApplication处理。

        （1）继承Application。

        （2）ProcessLifecycleOwner.getLifecycle().addObserver() 将观察者与被观察者绑定，即将自定义类与MyApplication绑定。

        step2.自定义类的处理

        （1）实现LIfecycleObserver接口。

        （2）添加标签注解事件，感知Application的生命周期。

4.2示例代码

        MyApplication.java。

package com.gaoting.processlifecycleapplication;import android.app.Application;import androidx.lifecycle.ProcessLifecycleOwner;public class MyApplication extends Application {ApplicationObserver mApplicationObserver;@Overridepublic void onCreate() {mApplicationObserver = new ApplicationObserver();ProcessLifecycleOwner.get().getLifecycle().addObserver(mApplicationObserver);super.onCreate();}
}

         观察者ApplicationObserver.java。

package com.gaoting.processlifecycleapplication;import android.util.Log;import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;public class ApplicationObserver implements LifecycleObserver {String TAG = "ApplicationObserver";/*** 整个应用程序只感知1次*/@OnLifecycleEvent(Lifecycle.Event.ON_CREATE)public  void onCreate(){Log.i(TAG,"ApplicationObserver.onCreate()应用程序启动");}/*** 应用程序打到前台*/@OnLifecycleEvent(Lifecycle.Event.ON_START)public  void onStart(){Log.i(TAG,"ApplicationObserver.onStart()应用程序在前台");}/*** 应用程序推到后台*/@OnLifecycleEvent(Lifecycle.Event.ON_RESUME)public  void onResume(){Log.i(TAG,"ApplicationObserver.onResume()应用程序在前台");}/*** 应用程序推到后台*/@OnLifecycleEvent(Lifecycle.Event.ON_PAUSE)public  void onPause(){Log.i(TAG,"ApplicationObserver.onPause()应用程序退到后台");}/*** 应用程序销毁，感知不到*/@OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)public  void onDestroy(){Log.i(TAG,"ApplicationObserver.onStop()应用程序销毁");}}

         AndroidManifest.xml中要增加一行:

                android:name=".MyApplication"。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"><applicationandroid:name=".MyApplication"android:allowBackup="true"android:dataExtractionRules="@xml/data_extraction_rules"android:fullBackupContent="@xml/backup_rules"android:icon="@mipmap/ic_launcher"android:label="@string/app_name"android:roundIcon="@mipmap/ic_launcher_round"android:supportsRtl="true"android:theme="@style/Theme.ProcessLifecycleApplication"tools:targetApi="31"><activityandroid:name=".MainActivity"android:exported="true"><intent-filter><action android:name="android.intent.action.MAIN" /><category android:name="android.intent.category.LAUNCHER" /></intent-filter></activity></application></manifest>

        测试，把应用启动，转入后台、回到前台等，然后观察Logcat打印日志。