Android灯光系统(4)——电池灯分析实验

一、电池事件的广播的注册

1.运行init进程创建SystemServer

2.一方面，创建BatteryService，获得电池灯，创建BatteryListener用来监听底层的上报事件。
(1)SystemServer.java : 
startCoreServices()
    mSystemServiceManager.startService(BatteryService.class);

(2)SystemServiceManager.java: 
startService()
    BatteryService() //构造函数
        mLed = new Led(context, getLocalService(LightsManager.class));
            Led()
                mBatteryLight = lights.getLight(LightsManager.LIGHT_ID_BATTERY);

    service.onStart(); //BatteryService.java
        /*
         * 电池监听器,当电池的属性发生变化的时候BatteryListener的batteryPropertiesChanged()
         * 就会被调用，它会去调用update()方法，然后调用sendIntentLockd()，然后调用updateLightsLocked()
         * 或设置电池属性。
         */
        batteryPropertiesRegistrar.registerListener(new BatteryListener());
        publishBinderService("battery", new BinderService());
        publishLocalService(BatteryManagerInternal.class, new LocalService());


3.另一方，创建PowerManagerService
SystemServer.java : 
startBootstrapServices()
    mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);

获得BatteryService
SystemServer.java: 
startOtherServices()
    mPowerManagerService.systemReady(mActivityManagerService.getAppOpsService()); //PowerManagerService.java
        mBatteryManagerInternal = getLocalService(BatteryManagerInternal.class);

        /* 注册电池广播接收器，监听ACTION_BATTERY_CHANGED */
        IntentFilter filter = new IntentFilter();
        filter.addAction(Intent.ACTION_BATTERY_CHANGED);
        filter.setPriority(IntentFilter.SYSTEM_HIGH_PRIORITY);
        /*
         * 池电量发生变化的时候BatteryReceiver的onReceiver()方法就会被调用。它最终会调用到
         * updatePowerStateLocked()
         */
        mContext.registerReceiver(new BatteryReceiver(), filter, null, mHandler);

二、电池事件的广播与处理

1.Linux驱动上报电池事件

2.BatteryListener的监听函数batteryPropertiesChanged被调用

3.广播ACTION_BATTERY_CHANGED更新电池灯，调用细节如下
(1)BatteryService.java: 
update()
    processValuesLocked(false);
        sendIntentLocked(); //①
        mLed.updateLightsLocked(); //②

①sendIntentLocked() //BatteryService.java
final Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED);
    mHandler.post(new Runnable() 
        @Override
        public void run() 
            ActivityManagerNative.broadcastStickyIntent(intent, null, UserHandle.USER_ALL);

    );


②updateLightsLocked() //BatteryService.java
    /*调用native方法设置LED*/
    mBatteryLight.setColor(mBatteryLowARGB);
    mBatteryLight.setFlashing(mBatteryLowARGB, Light.LIGHT_FLASH_TIMED, mBatteryLedOn, mBatteryLedOff);
    mBatteryLight.setColor(mBatteryFullARGB);
    mBatteryLight.setColor(mBatteryMediumARGB);
    mBatteryLight.turnOff();


4.收到广播消息后执行BatteryReceiver.onReceive，调用细节如下
(1)PowerManagerService.java: 
onReceive()
    handleBatteryStateChangedLocked();
        updatePowerStateLocked();

三、笔记

1.启动服务的流程

SystemServiceManager.startService(BatteryService.class); //SystemServer.java
    /*1.获取构造函数,然后构造这个service*/
    Constructor<T> constructor = serviceClass.getConstructor(Context.class);
    service = constructor.newInstance(mContext);

    /*2.调用add()将所有service放到链表ArrayList<SystemService>中*/
    ArrayList<SystemService>.add(service); 

    /*3.调用这个服务的onStart()函数*/
    service.onStart(); 

所以一个服务的启动，首先构造函数被调用，其次被调用的就是onStart()。

2.获取xml中系统定义的资源

BatteryService.java：Led()
mBatteryLowARGB = context.getResources().getInteger(com.android.internal.R.integer.config_notificationsBatteryLowARGB);

config_notificationsBatteryLowARGB定义在：
<integer name="config_notificationsBatteryLowARGB">0xFFFF0000</integer>   //base/core/res/res/values/config.xml

<java-symbol type="integer" name="config_notificationsBatteryLowARGB" />  //base/core/res/res/values/Symbols.xml

3.BatteryService中使用LightsService的方法

/*1.LightsService中使用publishLocalService来"发布"自己*/
mSystemServiceManager.startService(LightsService.class);
publishLocalService(LightsManager.class, mService);

/*2.BatteryService中来获取LightsService发布的Service*/
LightsManager lights = getLocalService(LightsManager.class);

/*3.获取LightsService的控制LED的方法并控制LED*/
Light mBatteryLight = lights.getLight(LightsManager.LIGHT_ID_BATTERY);
mBatteryLight.setColor(mBatteryLowARGB);
mBatteryLight.setFlashing(mBatteryLowARGB, Light.LIGHT_FLASH_TIMED, mBatteryLedOn, mBatteryLedOff);
mBatteryLight.turnOff();

四、例子App

由于Android5.1的电池灯和通知灯使用的是同一个LED，请见通知灯的Demo