公司最近在搞个KMS，鼓励大家技术分享。好吧，我是一个好员工，积极响应领导的各种要求。但是，这个我不会写的，你可以说我没有分享精神，可以说我技术水平low，我就是不会写。如果公司一定要强制要求我写，我也一定是乱写凑数，这完全不能怪我，只能怪这个无情的世界，无情的季节，无情的………….。（请不要问我具体的原因，谢谢！） 但是，有一个好朋友，在上面发表了一个电池低电处理的文章，我看了一下，确实是说的非常清楚，只是是一个比较低版本的代码流程，我在android 7.1的代码上看了一下，和他说的有一点出入，不过，这没有关系不影响我们来学习。 我可以不写，但是我们可以学习。

BatteryService.java

./frameworks/base/services/core/java/com/android/server/BatteryService.java 当电池电量少于我们配置的低电量警告值（config_lowBatteryWarningLevel）时，发送低电量通知，弹出低电量通知对话框。
./frameworks/base/core/res/res/values/config.xml <integer name="config_lowBatteryWarningLevel">15integer> 只我满足shouldSendBatteryLowLocked的条件就可以发送低电量通知： private boolean shouldSendBatteryLowLocked() { final boolean plugged = mPlugType != BATTERY_PLUGGED_NONE; final boolean oldPlugged = mLastPlugType != BATTERY_PLUGGED_NONE; /* 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). */ return !plugged && mBatteryProps.batteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN && mBatteryProps.batteryLevel <= mLowBatteryWarningLevel && (oldPlugged || mLastBatteryLevel > mLowBatteryWarningLevel); } 发送低电量通知Intent.ACTION_BATTERY_LOW： private void processValuesLocked(boolean force) if (shouldSendBatteryLowLocked()) { mSentLowBatteryBroadcast = true; mHandler.post(new Runnable() { @Override public void run() { Intent statusIntent = new Intent(Intent.ACTION_BATTERY_LOW); statusIntent.setFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT); mContext.sendBroadcastAsUser(statusIntent, UserHandle.ALL); } }); 当电量为0时，发出关闭通知Intent.ACTION_REQUEST_SHUTDOWN： private void shutdownIfWeakChargerEmptySOCLocked() { if (mBatteryProps.batteryLevel == 0) { if (mInitiateShutdown) { 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); }

PowerNotificationWarnings.java

./frameworks/base/packages/SystemUI/src/com/android/systemui/power/PowerNotificationWarnings.java 当电量低时，弹出低电量通知对话框： private void showWarningNotification() { final int textRes = R.string.battery_low_percent_format; final String percentage = NumberFormat.getPercentInstance().format((double) mBatteryLevel / 100.0); final Notification.Builder nb = new Notification.Builder(mContext) .setSmallIcon(R.drawable.ic_power_low) // Bump the notification when the bucket dropped. .setWhen(mBucketDroppedNegativeTimeMs) .setShowWhen(false) .setContentTitle(mContext.getString(R.string.battery_low_title)) .setContentText(mContext.getString(textRes, percentage)) .setOnlyAlertOnce(true) .setDeleteIntent(pendingBroadcast(ACTION_DISMISSED_WARNING)) .setPriority(Notification.PRIORITY_MAX) .setVisibility(Notification.VISIBILITY_PUBLIC) .setColor(mContext.getColor( com.android.internal.R.color.battery_saver_mode_color)); if (hasBatterySettings()) { nb.setContentIntent(pendingBroadcast(ACTION_SHOW_BATTERY_SETTINGS)); } nb.addAction(0, mContext.getString(R.string.battery_saver_start_action), pendingBroadcast(ACTION_START_SAVER)); if (mPlaySound) { attachLowBatterySound(nb); mPlaySound = false; } SystemUI.overrideNotificationAppName(mContext, nb); mNoMan.notifyAsUser(TAG_NOTIFICATION, R.id.notification_power, nb.build(), UserHandle.ALL); } 并播放低电量声音： private void attachLowBatterySound(Notification.Builder b) { final ContentResolver cr = mContext.getContentResolver(); final int silenceAfter = Settings.Global.getInt(cr, Settings.Global.LOW_BATTERY_SOUND_TIMEOUT, 0); final long offTime = SystemClock.elapsedRealtime() - mScreenOffTime; if (silenceAfter > 0 && mScreenOffTime > 0 && offTime > silenceAfter) { Slog.i(TAG, "screen off too long (" + offTime + "ms, limit " + silenceAfter + "ms): not waking up the user with low battery sound"); return; } if (DEBUG) { Slog.d(TAG, "playing low battery sound. pick-a-doop!"); // WOMP-WOMP is deprecated } if (Settings.Global.getInt(cr, Settings.Global.POWER_SOUNDS_ENABLED, 1) == 1) { final String soundPath = Settings.Global.getString(cr, Settings.Global.LOW_BATTERY_SOUND); if (soundPath != null) { final Uri soundUri = Uri.parse("file://" + soundPath); if (soundUri != null) { b.setSound(soundUri, AUDIO_ATTRIBUTES); if (DEBUG) Slog.d(TAG, "playing sound " + soundUri); } } } } 我们一般在配置文件中设置低电量的声音文件和超时时间：
./frameworks/base/packages/SettingsProvider/res/values/defaults.xml <string name="def_low_battery_sound" translatable="false">/system/media/audio/ui/LowBattery.oggstring>