PowerUI是SystemUI控制电量提醒的模块，包括低电提醒和高低温关机提醒。
初始化
PowerUI继承SystemUI，故在SystemUI启动时，PowerUI也会随之调用start()，其代码如下：
public void start() {
// 获取PowerManager
mPowerManager = (PowerManager) mContext.getSystemService(Context.POWER_SERVICE);
// 获取HardwarePorpertiesManger 以便获取当前手机温度
mHardwarePropertiesManager = (HardwarePropertiesManager)
mContext.getSystemService(Context.HARDWARE_PROPERTIES_SERVICE);
mScreenOffTime = mPowerManager.isScreenOn() ? -1 : SystemClock.elapsedRealtime();
// 获取WarningsUI实例
mWarnings = Dependency.get(WarningsUI.class);
mLastConfiguration.setTo(mContext.getResources().getConfiguration());
// 注册低电系统阈值变化观察者
ContentObserver obs = new ContentObserver(mHandler) {
@Override
public void onChange(boolean selfChange) {
updateBatteryWarningLevels();
}
};
final ContentResolver resolver = mContext.getContentResolver();
resolver.registerContentObserver(Settings.Global.getUriFor(
Settings.Global.LOW_POWER_MODE_TRIGGER_LEVEL),
false, obs, UserHandle.USER_ALL);
// 初始化低电警告阈值
updateBatteryWarningLevels();
// 初始化电量相关信息广播接收者
mReceiver.init();
// Check to see if we need to let the user know that the phone previously shut down due
// to the temperature being too high.
showThermalShutdownDialog();
// 初始化温度警告阈值
initTemperatureWarning();
}
从上面不难看出，PowerUI两个功能：
一、监听电量变化，发出低电警告；
二、监听电池温度变化，发出温度警告。
低电警告
在start()时，会进行updateBatteryWarningLevels()，其代码如下:
void updateBatteryWarningLevels() {
int critLevel = mContext.getResources().getInteger(
com.android.internal.R.integer.config_criticalBatteryWarningLevel);
final ContentResolver resolver = mContext.getContentResolver();
int defWarnLevel = mContext.getResources().getInteger(
com.android.internal.R.integer.config_lowBatteryWarningLevel);
int warnLevel = Settings.Global.getInt(resolver,
Settings.Global.LOW_POWER_MODE_TRIGGER_LEVEL, defWarnLevel);
if (warnLevel == 0) {
warnLevel = defWarnLevel;
}
if (warnLevel < critLevel) {
warnLevel = critLevel;
}
mLowBatteryReminderLevels[0] = warnLevel;
mLowBatteryReminderLevels[1] = critLevel;
mLowBatteryAlertCloseLevel = mLowBatteryReminderLevels[0]
+ mContext.getResources().getInteger(
com.android.internal.R.integer.config_lowBatteryCloseWarningBump);
}
这里有两个值需要关注：warnLevel和critLevel，warnLevel默认值是15，可以随系统数据库字段LOW_POWER_MODE_TRIGGER_LEVEL对应值而改变，其主要作用为进入低电警告的阈值。critLevel默认值是5，其主要作用是打开低电保护的阈值。这两个值都被写入数组mLowBatteryReminderLevels[]，用来计算是否需要显示或者更新低电提醒。
那什么时候触发低电警告呢？可以看到，在初始化的时候，PowerUI会去注册一个广播接收者，代码如下：
private final class Receiver extends BroadcastReceiver {
public void init() {
// Register for Intent broadcasts for...
IntentFilter filter = new IntentFilter();
filter.addAction(Intent.ACTION_BATTERY_CHANGED);
filter.addAction(Intent.ACTION_SCREEN_OFF);
filter.addAction(Intent.ACTION_SCREEN_ON);
filter.addAction(Intent.ACTION_USER_SWITCHED);
mContext.registerReceiver(this, filter, null, mHandler);
}
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (action.equals(Intent.ACTION_BATTERY_CHANGED)) {
final int oldBatteryLevel = mBatteryLevel;
mBatteryLevel = intent.getIntExtra(BatteryManager.EXTRA_LEVEL, 100);
final int oldBatteryStatus = mBatteryStatus;
mBatteryStatus = intent.getIntExtra(BatteryManager.EXTRA_STATUS,
BatteryManager.BATTERY_STATUS_UNKNOWN);
final int oldPlugType = mPlugType;
mPlugType = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 1);
final int oldInvalidCharger = mInvalidCharger;
mInvalidCharger = intent.getIntExtra(BatteryManager.EXTRA_INVALID_CHARGER, 0);
final boolean plugged = mPlugType != 0;
final boolean oldPlugged = oldPlugType != 0;
int oldBucket = findBatteryLevelBucket(oldBatteryLevel);
int bucket = findBatteryLevelBucket(mBatteryLevel);
if (DEBUG) {
Slog.d(TAG, "buckets ....." + mLowBatteryAlertCloseLevel
+ " .. " + mLowBatteryReminderLevels[0]
+ " .. " + mLowBatteryReminderLevels[1]);
Slog.d(TAG, "level " + oldBatteryLevel + " --> " + mBatteryLevel);
Slog.d(TAG, "status " + oldBatteryStatus + " --> " + mBatteryStatus);
Slog.d(TAG, "plugType " + oldPlugType + " --> " + mPlugType);
Slog.d(TAG, "invalidCharger " + oldInvalidCharger + " --> " + mInvalidCharger);
Slog.d(TAG, "bucket " + oldBucket + " --> " + bucket);
Slog.d(TAG, "plugged " + oldPlugged + " --> " + plugged);
}
mWarnings.update(mBatteryLevel, bucket, mScreenOffTime);
if (oldInvalidCharger == 0 && mInvalidCharger != 0) {
Slog.d(TAG, "showing invalid charger warning");
mWarnings.showInvalidChargerWarning();
return;
} else if (oldInvalidCharger != 0 && mInvalidCharger == 0) {
mWarnings.dismissInvalidChargerWarning();
} else if (mWarnings.isInvalidChargerWarningShowing()) {
// if invalid charger is showing, don't show low battery
return;
}
boolean isPowerSaver = mPowerManager.isPowerSaveMode();
if (!plugged
&& !isPowerSaver
&& (bucket < oldBucket || oldPlugged)
&& mBatteryStatus != BatteryManager.BATTERY_STATUS_UNKNOWN
&& bucket < 0) {
// only play SFX when the dialog comes up or the bucket changes
final boolean playSound = bucket != oldBucket || oldPlugged;
mWarnings.showLowBatteryWarning(playSound);
} else if (isPowerSaver || plugged || (bucket > oldBucket && bucket > 0)) {
mWarnings.dismissLowBatteryWarning();
} else {
mWarnings.updateLowBatteryWarning();
}
} else if (Intent.ACTION_SCREEN_OFF.equals(action)) {
mScreenOffTime = SystemClock.elapsedRealtime();
} else if (Intent.ACTION_SCREEN_ON.equals(action)) {
mScreenOffTime = -1;
} else if (Intent.ACTION_USER_SWITCHED.equals(action)) {
mWarnings.userSwitched();
} else {
Slog.w(TAG, "unknown intent: " + intent);
}
}
};
可以看到当收到ACTION_BATTERY_CHANGED的广播时，将进行一系列的flag判断，如是否开启电量保护、是否usb插入以及对当前电量的判断，这里电量判断通过一个bucket值来进行判断是否属于健康电量，其判断逻辑如下：
/**
* Buckets the battery level.
*
* The code in this function is a little weird because I couldn't comprehend
* the bucket going up when the battery level was going down. --joeo
*
* 1 means that the battery is "ok"
* 0 means that the battery is between "ok" and what we should warn about.
* less than 0 means that the battery is low
*/
private int findBatteryLevelBucket(int level) {
if (level >= mLowBatteryAlertCloseLevel) {
return 1;
}
if (level > mLowBatteryReminderLevels[0]) {
return 0;
}
final int N = mLowBatteryReminderLevels.length;
for (int i=N-1; i>=0; i--) {
if (level <= mLowBatteryReminderLevels[i]) {
return -1-i;
}
}
throw new RuntimeException("not possible!");
}
这里用到了之前介绍的mLowBatteryReminderLevels[]判断，即warnLevel和critLevel两个值进行判断，当return值小于0则认为当前电量不健康。从而触发低电警告。
高温警告
高温警告触发于电池温度过高时，会提示用户电池温度过高，将设备关机。初始化逻辑如下:
private void initTemperatureWarning() {
ContentResolver resolver = mContext.getContentResolver();
Resources resources = mContext.getResources();
if (Settings.Global.getInt(resolver, Settings.Global.SHOW_TEMPERATURE_WARNING,
resources.getInteger(R.integer.config_showTemperatureWarning)) == 0) {
return;
}
mThresholdTemp = Settings.Global.getFloat(resolver, Settings.Global.WARNING_TEMPERATURE,
resources.getInteger(R.integer.config_warningTemperature));
if (mThresholdTemp < 0f) {
// Get the throttling temperature. No need to check if we're not throttling.
float[] throttlingTemps = mHardwarePropertiesManager.getDeviceTemperatures(
HardwarePropertiesManager.DEVICE_TEMPERATURE_SKIN,
HardwarePropertiesManager.TEMPERATURE_SHUTDOWN);
if (throttlingTemps == null
|| throttlingTemps.length == 0
|| throttlingTemps[0] == HardwarePropertiesManager.UNDEFINED_TEMPERATURE) {
return;
}
mThresholdTemp = throttlingTemps[0] -
resources.getInteger(R.integer.config_warningTemperatureTolerance);
}
setNextLogTime();
// This initialization method may be called on a configuration change. Only one set of
// ongoing callbacks should be occurring, so remove any now. updateTemperatureWarning will
// schedule an ongoing callback.
mHandler.removeCallbacks(mUpdateTempCallback);
// We have passed all of the checks, start checking the temp
updateTemperatureWarning();
}
通过这个获取高温警告阈值，供其在updateTemperatureWarning()中进行判断，其代码如下：
// We create a method reference here so that we are guaranteed that we can remove a callback
// by using the same instance (method references are not guaranteed to be the same object
// each time they are created).
private final Runnable mUpdateTempCallback = this::updateTemperatureWarning;
protected void updateTemperatureWarning() {
float[] temps = mHardwarePropertiesManager.getDeviceTemperatures(
HardwarePropertiesManager.DEVICE_TEMPERATURE_SKIN,
HardwarePropertiesManager.TEMPERATURE_CURRENT);
if (temps.length != 0) {
float temp = temps[0];
mRecentTemps[mNumTemps++] = temp;
StatusBar statusBar = getComponent(StatusBar.class);
if (statusBar != null && !statusBar.isDeviceInVrMode()
&& temp >= mThresholdTemp) {
logAtTemperatureThreshold(temp);
mWarnings.showHighTemperatureWarning();
} else {
mWarnings.dismissHighTemperatureWarning();
}
}
logTemperatureStats();
mHandler.postDelayed(mUpdateTempCallback, TEMPERATURE_INTERVAL);
}
并且将该方法加入Looper中，这里的TEMPERATURE_INTERVAL=30s，即表示每30s进行一次设备电池温度的获取，并判断是否需要发出高温警告。
小结
PowerUI是SystemUI中监听系统电池模块状态，并以UI形式展现出来的一种框架。如果在定制修改中需要监听系统的某些模块的状态，同样可以采取类似框架进行客制化处理。