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Android?通過BatteryService對電量進行自動管理。在BatteryService.java中從jni層獲得電量mBatteryLevel, ?并根據mBatteryLevel判斷手機電量是否過低，然后發出警告或聲音提醒，并且太低時還會自動關機。下面簡單介紹一下其流程。

? ? ? ?在BatteryService.java中判斷當前電量是否過低:

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/*?The?ACTION_BATTERY_LOW?broadcast?is?sent?in?these?situations:?

?*?-?is?just?un-plugged?(previously?was?plugged)?and?battery?level?is?

?*???less?than?or?equal?to?WARNING,?or?

?*?-?is?not?plugged?and?battery?level?falls?to?WARNING?boundary?

?*???(becomes?<=?mLowBatteryWarningLevel).?

?*/??

final?boolean?sendBatteryLow?=?!plugged??

????????&&?mBatteryStatus?!=?BatteryManager.BATTERY_STATUS_UNKNOWN??

????????&&?mBatteryLevel?<=?mLowBatteryWarningLevel??

????????&&?(oldPlugged?||?mLastBatteryLevel?>?mLowBatteryWarningLevel);??

如果當前電量小于警告電量（在config.xml中 <integer name="config_lowBatteryWarningLevel">15</integer>）則彈出電量低提示，或者電量為0（當然這個有誤差也可能是5%時就自動關機）時自動關機。如果低電量的話就發送一個廣播出去：

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if?(sendBatteryLow)?{??

????mSentLowBatteryBroadcast?=?true;??

????statusIntent.setAction(Intent.ACTION_BATTERY_LOW);??

????mContext.sendBroadcast(statusIntent);??

}??

? ? ? ? 下面這段代碼是電量過低而自動關機：

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private?void?More?...shutdownIfNoPowerLocked()?{??

????//?shut?down?gracefully?if?our?battery?is?critically?low?and?we?are?not?powered.??

????//?wait?until?the?system?has?booted?before?attempting?to?display?the?shutdown?dialog.??

????if?(mBatteryLevel?==?0?&&?!isPoweredLocked(BatteryManager.BATTERY_PLUGGED_ANY))?{??

????????mHandler.post(new?Runnable()?{??

????????????@Override??

????????????public?void?More?...run()?{??

????????????????if?(ActivityManagerNative.isSystemReady())?{??

????????????????????Intent?intent?=?new?Intent(Intent.ACTION_REQUEST_SHUTDOWN);??

????????????????????intent.putExtra(Intent.EXTRA_KEY_CONFIRM,?false);??

????????????????????intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);??

????????????????????mContext.startActivityAsUser(intent,?UserHandle.CURRENT);??

????????????????}??

????????????}??

????????});??

????}??

}??

? ? ? ? 而在StatusBarPolicy.java中會接收廣播,?里面有判斷當接受到ACTION_BATTERY_LOW時, 調用onBatteryLow(intent)方法來處理：

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private?BroadcastReceiver?mIntentReceiver?=?new?BroadcastReceiver()?{??

????????@Override??

????????public?void?onReceive(Context?context,?Intent?intent)?{??

????????????String?action?=?intent.getAction();??

????????????.....action.??

????????????//里面會有判斷當接受到ACTION_BATTERY_LOW時：??

????????????else?if?(action.equals(Intent.ACTION_BATTERY_LOW))?{??

????????????????onBatteryLow(intent);??

????????????}??

????????}??

????}??

??????

????private?void?onBatteryLow(Intent?intent)?{??

????????if?(SHOW_LOW_BATTERY_WARNING)?{??

????????????if?(false)?{??

????????????????Slog.d(TAG,?"mPhoneState="?+?mPhoneState??

????????????????????????+?"?mLowBatteryDialog="?+?mLowBatteryDialog??

????????????????????????+?"?mBatteryShowLowOnEndCall="?+?mBatteryShowLowOnEndCall);??

????????????}??

??

????????????if?(SHOW_BATTERY_WARNINGS_IN_CALL?||?mPhoneState?==?TelephonyManager.CALL_STATE_IDLE)?{??

????????????????showLowBatteryWarning();??

????????????}?else?{??

????????????????mBatteryShowLowOnEndCall?=?true;??

????????????}??

????????}??

????}??

? ? ? ? ?彈出低電量過低Dialog提醒和聲音提醒：

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private?void?showLowBatteryWarning()?{??

????closeLastBatteryView();??

??

????//?Show?exact?battery?level.??

????CharSequence?levelText?=?mContext.getString(R.string.battery_low_percent_format,?mBatteryLevel);??

??

????if?(mBatteryLevelTextView?!=?null)?{??

????????mBatteryLevelTextView.setText(levelText);??

????}?else?{??

????????View?v?=?View.inflate(mContext,?R.layout.battery_low,?null);??

????????mBatteryLevelTextView=(TextView)v.findViewById(R.id.level_percent);??

????????mBatteryLevelTextView.setText(levelText);??

????????AlertDialog.Builder?b?=?new?AlertDialog.Builder(mContext);??

????????b.setCancelable(true);??

????????b.setTitle(R.string.battery_low_title);??

????????b.setView(v);??

????????b.setIcon(android.R.drawable.ic_dialog_alert);??

????????b.setPositiveButton(android.R.string.ok,?null);??

??

????????final?Intent?intent?=?new?Intent(Intent.ACTION_POWER_USAGE_SUMMARY);??

????????intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK??

????????????????|?Intent.FLAG_ACTIVITY_MULTIPLE_TASK??

????????????????|?Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS??

????????????????|?Intent.FLAG_ACTIVITY_NO_HISTORY);??

????????if?(intent.resolveActivity(mContext.getPackageManager())?!=?null)?{??

????????????b.setNegativeButton(R.string.battery_low_why,?new?DialogInterface.OnClickListener()?{??

????????????????@Override??

????????????????public?void?onClick(DialogInterface?dialog,?int?which)?{??

????????????????????mContext.startActivity(intent);??

????????????????????if?(mLowBatteryDialog?!=?null)?{??

????????????????????????mLowBatteryDialog.dismiss();??

????????????????????}??

????????????????}??

????????????});??

????????}??

??

????????AlertDialog?d?=?b.create();??

????????d.setOnDismissListener(mLowBatteryListener);??

????????d.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);??

????????d.show();??

????????mLowBatteryDialog?=?d;??

????}??

??????

????//waring?voiced??

????final?ContentResolver?cr?=?mContext.getContentResolver();??

????if?(Settings.System.getInt(cr,?Settings.System.POWER_SOUNDS_ENABLED,?1)?==?1)?{??

????????final?String?soundPath?=?Settings.System.getString(cr,?Settings.System.LOW_BATTERY_SOUND);??

????????if?(soundPath?!=?null)?{??

????????????final?Uri?soundUri?=?Uri.parse("file://"?+?soundPath);??

????????????if?(soundUri?!=?null)?{??

????????????????final?Ringtone?sfx?=?RingtoneManager.getRingtone(mContext,?soundUri);??

????????????????if?(sfx?!=?null)?{??

????????????????????sfx.setStreamType(AudioManager.STREAM_SYSTEM);??

????????????????????sfx.play();??

????????????????}??

????????????}??

????????}??

????}??

}??

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