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Android Low Battery 低电量处理流程
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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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???????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：[java]?view plaincopy
private?void?More?...shutdownIfNoPowerLocked()?{??????????????????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.????????????????????????????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：[java]?view plaincopy
private?void?showLowBatteryWarning()?{??????closeLastBatteryView();??????????????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;??????}??????????????????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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