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"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <ImageView
        android:id="@+id/container_image"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

manifest.xml

<service
    android:name=".HelloService"></service>

<receiver android:name=".HelloWorld">
    <intent-filter>
        <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
    </intent-filter>

    <meta-data
        android:name="android.appwidget.provider"
        android:resource="@xml/hello_world_info" />
</receiver>

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