想写一个根据电量来切换图片的AppWidget，由于监视电量需要另起一个service，我的想法是在添加第一个widget时启动service，在删除最后一个时结束service。

layout<?xml version="1.0" encoding="utf-8"?>

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical">

android:id="@+id/container_image"

android:layout_width="match_parent"

android:layout_height="match_parent" />

manifest.xml

android:name=".HelloService">

android:name="android.appwidget.provider"

android:resource="@xml/hello_world_info" />

AppWidgetProvider代码如下：

/**

* 广播接收器

*/

public class HelloWorld extends AppWidgetProvider {

private static String mShuouyang = "shuouyang";

/**

* @param context

* @param appWidgetManager

* @param appWidgetIds 一个桌面程序可能被安放好几个

*/

@Override

public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {

// There may be multiple widgets active, so update all of them

Log.d(mShuouyang, "广播========onUpdate: =======");

super.onUpdate(context, appWidgetManager, appWidgetIds);

}

@Override

public void onEnabled(Context context) {

Log.d(mShuouyang, "广播======== onEnabled: =======");

Intent mIntent = new Intent(context, HelloService.class);

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {

context.startForegroundService(mIntent);

} else {

context.startService(mIntent);

}

Log.d(mShuouyang, "广播========启动了Service: =======");

// Enter relevant functionality for when the first widget is created

}

@Override

public void onDisabled(Context context) {

// Enter relevant functionality for when the last widget is disabled

Log.d(mShuouyang, "广播======== onDisabled: =======");

context.stopService(new Intent(context, HelloService.class));//停止service

// context.stopService(mIntent);

}

@Override

public void onReceive(Context context, Intent intent) {

Log.d(mShuouyang, "广播======== onReceive: =======");

super.onReceive(context, intent);

}

}

在service中，注册一个匿名内部类的广播接收器来接收电量后更具电量显示图片public class HelloService extends Service {

private static BroadcastReceiver mBroadcastReceiver;

public HelloService() {

}

@Override

public IBinder onBind(Intent intent) {

// TODO: Return the communication channel to the service.

throw new UnsupportedOperationException("Not yet implemented");

}

@Override

public void onCreate() {

super.onCreate();

mBroadcastReceiver = new BroadcastReceiver() {

private int[] drawables = {

R.drawable.helloworld0,

R.drawable.helloworld1,

R.drawable.helloworld2,

R.drawable.helloworld3,

R.drawable.helloworld4,

R.drawable.helloworld5,

R.drawable.helloworld6,

R.drawable.helloworld7,

R.drawable.helloworld8,

R.drawable.helloworld9,

R.drawable.helloworld10,

};

int percent = 5;//当前电量标志

int level = 0; //当前电量

int scale = 100;//总电量

@Override

public void onReceive(Context context, Intent intent) {

String action = intent.getAction();

try {

if (action.equals("android.intent.action.BATTERY_CHANGED")) {

this.level = intent.getExtras().getInt("level", 0);//当前电量

this.scale = intent.getExtras().getInt("scale", 100);//总电量

this.percent = level *10/scale;

Log.d("shuouyang", "服务 onReceive: 获取到了电量信息"+ percent);

}

AppWidgetManager instance = AppWidgetManager.getInstance(context);

ComponentName componentName = new ComponentName(context, HelloWorld.class);

RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.hello_world);

remoteViews.setImageViewResource(R.id.container_image,drawables[this.percent]);

instance.updateAppWidget(componentName,remoteViews);

Log.d("shuouyang", "服务 onReceive: 逻辑通知完成");

}catch (Exception e){

e.printStackTrace();

Toast.makeText(context,"未获取到电量",Toast.LENGTH_SHORT).show();

}

}

};

}

@Override

public void onStart(Intent intent, int startId) {

super.onStart(intent, startId);

IntentFilter intentFilter = new IntentFilter("android.intent.action.BATTERY_CHANGED");

registerReceiver(mBroadcastReceiver,intentFilter);//注册接收电量改变的广播接收器

}

@Override

public void onDestroy() {

Log.d("shuouyang", "服务 onDestroy: 服务被销毁");

unregisterReceiver(mBroadcastReceiver);//解除注册

super.onDestroy();

}

}

启动成功

当我将wigget添加到桌面时，开始几秒(通过AVD的外部控制器修改电量)可以根据此时电量显示指定图片和切换图片，后面就切换不了了，只能显示固定的一张图片。查看log显示，service内部的广播接收器在初始几秒就收了几次广播后就自动onDestroy了。不明白是什么停止了服务，

log如下

20-08-19 13:07:50.614 9319-9319/? D/xxxxxx: 广播======== onReceive: =======

2020-08-19 13:07:50.629 9319-9319/? D/xxxxxx: 广播======== onReceive: =======

2020-08-19 13:07:50.629 9319-9319/? D/xxxxxx: 广播========onUpdate: =======

2020-08-19 13:07:50.629 9319-9319/? D/xxxxxx: 广播========启动了Service: =======

2020-08-19 13:07:50.630 9319-9319/? D/xxxxxx: 服务 onReceive: 获取到了电量信息8

2020-08-19 13:07:50.633 9319-9319/? D/xxxxxx: 服务 onReceive: 逻辑通知完成

2020-08-19 13:07:55.327 9319-9319/com.shu.helloworld D/xxxxxx: 服务 onReceive: 获取到了电量信息7

2020-08-19 13:07:55.329 9319-9319/com.shu.helloworld D/xxxxxx: 服务 onReceive: 逻辑通知完成

2020-08-19 13:07:55.620 9319-9319/com.shu.helloworld D/xxxxxx: 服务 onDestroy: 服务被销毁