電池的信息,電壓,溫度,充電狀態等等,都是由BatteryService來提供的。BatteryService是跑在system_process當中,在系統初始化的時候啓動,如下
在SystemServer.java中可以看到啓動BatteryService的代碼:
Log.i(TAG, \"Starting Battery Service.\"); BatteryService battery = new BatteryService(context); ServiceManager.addService(\"battery\", battery);
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1. 數據來源
BatteryService通過JNI(com_android_server_BatteryService.cpp)讀取數據。BatteryService通過JNI註冊的不僅有函數,還有變量。 如下:
//##############在BatteryService.java中聲明的變量################
privateboolean mAcOnline; privateboolean mUsbOnline; privateint mBatteryStatus; privateint mBatteryHealth; privateboolean mBatteryPresent; privateint mBatteryLevel; privateint mBatteryVoltage; privateint mBatteryTemperature; private String mBatteryTechnology;
//在BatteryService.java中聲明的變量,在com_android_server_BatteryService.cpp中共用,即在com_android_server_BatteryService.cpp中其實操作的也是BatteryService.java中聲明的變量
gFieldIds.mAcOnline = env->GetFieldID(clazz, \"mAcOnline\", \"Z\"); gFieldIds.mUsbOnline = env->GetFieldID(clazz, \"mUsbOnline\", \"Z\"); gFieldIds.mBatteryStatus = env->GetFieldID(clazz, \"mBatteryStatus\", \"I\"); gFieldIds.mBatteryHealth = env->GetFieldID(clazz, \"mBatteryHealth\", \"I\"); gFieldIds.mBatteryPresent = env->GetFieldID(clazz, \"mBatteryPresent\", \"Z\"); gFieldIds.mBatteryLevel = env->GetFieldID(clazz, \"mBatteryLevel\", \"I\"); gFieldIds.mBatteryTechnology = env->GetFieldID(clazz, \"mBatteryTechnology\", \"Ljava/lang/String;\"); gFieldIds.mBatteryVoltage = env->GetFieldID(clazz, \"mBatteryVoltage\", \"I\"); gFieldIds.mBatteryTemperature = env->GetFieldID(clazz, \"mBatteryTemperature\", \"I\");
//上面這些變量的值,對應是從下面的文件中讀取的,一隻文件存儲一個數值。
#define AC_ONLINE_PATH "/sys/class/power_supply/ac/online"#define USB_ONLINE_PATH "/sys/class/power_supply/usb/online"#define BATTERY_STATUS_PATH "/sys/class/power_supply/battery/status"#define BATTERY_HEALTH_PATH "/sys/class/power_supply/battery/health"#define BATTERY_PRESENT_PATH "/sys/class/power_supply/battery/present"#define BATTERY_CAPACITY_PATH "/sys/class/power_supply/battery/capacity"#define BATTERY_VOLTAGE_PATH "/sys/class/power_supply/battery/batt_vol"#define BATTERY_TEMPERATURE_PATH "/sys/class/power_supply/battery/batt_temp"#define BATTERY_TECHNOLOGY_PATH "/sys/class/power_supply/battery/technology"
Android是運行在Linux內核上面的,/sys/class/power_supply亦是Linux內核下面的目錄。至於這些文件時怎麼生成的,則是由Platform來控制的。
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2. 數據傳送
電池的這些信息是通過何種方式,被其他應用所獲得的。可以想到的有兩種方式,第一種,應用主動從BatteryService獲得數據;第二種,BatteryService主動把數據傳送給所關心的應用程序。
BatteryService採用的是第二種方式,所有的電池的信息數據是通過Intent傳送出去的。在BatteryService.java中,Code如下:
Intent intent = new Intent(Intent.ACTION_BATTERY_CHANGED); intent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY); intent.putExtra("status", mBatteryStatus); intent.putExtra("health", mBatteryHealth); intent.putExtra("present", mBatteryPresent); intent.putExtra("level", mBatteryLevel); intent.putExtra("scale", BATTERY_SCALE); intent.putExtra("icon-small", icon); intent.putExtra("plugged", mPlugType); intent.putExtra("voltage", mBatteryVoltage); intent.putExtra("temperature", mBatteryTemperature); intent.putExtra("technology", mBatteryTechnology); ActivityManagerNative.broadcastStickyIntent(intent, null);
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3. 數據接收
應用如果想要接收到BatteryService發送出來的電池信息,則需要註冊一個Intent爲Intent.ACTION_BATTERY_CHANGED的BroadcastReceiver。
註冊方法如下:
IntentFilter mIntentFilter = new IntentFilter(); mIntentFilter.addAction(Intent.ACTION_BATTERY_CHANGED); registerReceiver(mIntentReceiver, mIntentFilter); private BroadcastReceiver mIntentReceiver = new BroadcastReceiver() { @Override publicvoid onReceive(Context context, Intent intent) { // TODO Auto-generated method stub String action = intent.getAction(); if (action.equals(Intent.ACTION_BATTERY_CHANGED)) { int nVoltage = intent.getIntExtra("voltage", 0); if(nVoltage!=0){ mVoltage.setText("V: " + nVoltage + "mV - Success..."); } else{ mVoltage.setText("V: " + nVoltage + "mV - fail..."); } } } };
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4. 數據更新
電池的信息會隨着時間不停變化,自然地,就需要考慮如何實時的更新電池的數據信息。在BatteryService啓動的時候,會同時通過UEventObserver啓動一個onUEvent Thread。
每一個Process最多只能有一個onUEvent Thread,即使這個Process中有多個UEventObserver的實例。當在一個Process中,第一次Call startObserving()方法後,這個UEvent thread就啓動了。
而一旦這個UEvent thread啓動之後,就不會停止。
//在BatteryService.java中
mUEventObserver.startObserving("SUBSYSTEM=power_supply"); private UEventObserver mUEventObserver = new UEventObserver() { @Overridepublicvoid onUEvent(UEventObserver.UEvent event) { update(); } };
在UEvent thread中會不停調用 update()方法,來更新電池的信息數據。