PowerManager.WakeLock

PowerManager.WakeLock

　　PowerManager.WakerLock是我分析Standup Timer源代码时发现的一个小知识点，Standup Timer 用WakeLock保证程序运行时保持手机屏幕的恒亮（程序虽小但也做得相当的细心，考虑的很周到）。PowerManager 和PowerManager.WakerLock7用于对Android设备的电源进行管理。

　　 PowerManager:This class gives you control of the power state of the device.

　　 PowerManager.WakeLock:  lets you say that you need to have the device on.

　　Android中通过各种Lock锁对电源进行控制，需要注意的是加锁和解锁必须成对出现。先上一段Standup Timer里的代码然后进行说明。

代码

private  void  acquireWakeLock() {
if  (wakeLock  ==  null ) {
Logger.d( " Acquiring wake lock " );
PowerManager pm  =  (PowerManager) getSystemService(Context.POWER_SERVICE);
wakeLock  =  pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, this .getClass().getCanonicalName());
wakeLock.acquire();
}

}


private  void  releaseWakeLock() {
if  (wakeLock  !=  null  &&  wakeLock.isHeld()) {
wakeLock.release();
wakeLock  =  null ;
}

}

 

acquireWakeLock()方法中获取了  SCREEN_DIM_WAKE_LOCK锁，该锁使 CPU 保持运转，屏幕保持亮度（可以变灰）。这个函数在Activity的 onResume中被调用。releaseWakeLock()方法则是释放该锁。它在Activity的 onPause中被调用。利用Activiy的生命周期，巧妙的让  acquire()和release()成对出现。

@Override
protected  void  onResume()
{
super .onResume();
// 获取锁，保持屏幕亮度
acquireWakeLock();
startTimer();
}

代码

 

PowerManager和WakeLock的操作步骤

1. 　　PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);通过 Context.getSystemService().方法获取PowerManager实例。
2. 　　然后通过PowerManager的newWakeLock((intflags, String tag)来生成WakeLock实例。intFlags指示要获取哪种WakeLock，不同的Lock对cpu 、屏幕、键盘灯有不同影响。
3. 　　获取WakeLock实例后通过acquire()获取相应的锁，然后进行其他业务逻辑的操作，最后使用release()释放（释放是必须的）。

关于int flags

　　各种锁的类型对CPU 、屏幕、键盘的影响：

PARTIAL_WAKE_LOCK:保持CPU 运转，屏幕和键盘灯有可能是关闭的。

SCREEN_DIM_WAKE_LOCK：保持CPU 运转，允许保持屏幕显示但有可能是灰的，允许关闭键盘灯

SCREEN_BRIGHT_WAKE_LOCK：保持CPU 运转，允许保持屏幕高亮显示，允许关闭键盘灯

FULL_WAKE_LOCK：保持CPU 运转，保持屏幕高亮显示，键盘灯也保持亮度

ACQUIRE_CAUSES_WAKEUP：Normal wake locks don't actually turn on the illumination. Instead, they cause the illumination to remain on once it turns on (e.g. from user activity). This flag will force the screen and/or keyboard to turn on immediately, when the WakeLock is acquired. A typical use would be for notifications which are important for the user to see immediately.

ON_AFTER_RELEASE：f this flag is set, the user activity timer will be reset when the WakeLock is released, causing the illumination to remain on a bit longer. This can be used to reduce flicker if you are cycling between wake lock conditions.

权限获取

要进行电源的操作需要在AndroidManifest.xml中声明该应用有设置电源管理的权限。

< uses-permission  android:name ="android.permission.WAKE_LOCK"  />
你可能还需要
< uses-permission  android:name ="android.permission.DEVICE_POWER"  />

另外WakeLock的设置是 Activiy 级别的，不是针对整个Application应用的。

*如果你获得一个不完整的wakelock，则CPU会继续运行，不必顾及任何计时器甚至用户按下power键后。对于所有的其他的wakelock，CPU在运行，但用户可以直接用power键使设备休眠。

*If you hold a partial wakelock, the CPU will continue to run, irrespective of any timers and even after the user presses the power button. In all other wakelocks, the CPU will run, but the user can still put the device to sleep using the power button.

 

另外，你能加两个以上的标志，这些仅能影响屏幕的行为。这些标志当组合中有一个PARTIAL_WAKE_LOCK时将没有效果。

In addition, you can add two more flags, which affect behavior of the screen only. These flags have no effect when combined with a PARTIAL_WAKE_LOCK.

Flag Value	Description
ACQUIRE_CAUSES_WAKEUP	正常的wake lock不会实际转到照明。反而，他们使照明保持自他打开时（例如，来自用户activity）。这个标志会强制屏幕和/或键盘立即打开，当这个wakelock已获取时。一个典型用法是将哪些重要的通知立即让用户看到。 Normal wake locks don't actually turn on the illumination. Instead, they cause the illumination to remain on once it turns on (e.g. from user activity). This flag will force the screen and/or keyboard to turn on immediately, when the WakeLock is acquired. A typical use would be for notifications which are important for the user to see immediately.
ON_AFTER_RELEASE	如果这个标志被设置，用户activity计时器当WakeLock被释放时会重新设定，因为照明保持一点长。这个可以用于降低闪烁如果你是在wake lock状态下循环。 If this flag is set, the user activity timer will be reset when the WakeLock is released, causing the illumination to remain on a bit longer. This can be used to reduce flicker if you are cycling between wake lock conditions.

Summary

Nested Classes
class	PowerManager.WakeLock	类让你说你需要有这个设备。 Class lets you say that you need to have the device on.

Constants
int	ACQUIRE_CAUSES_WAKEUP	正常的wake lock不会实际的唤醒设备，他们自他准备好则保持着。 Normally wake locks don't actually wake the device, they just cause it to remain on once it's already on.
int	FULL_WAKE_LOCK	Wake lock 以确保屏幕和键盘全部点亮。 Wake lock that ensures that the screen and keyboard are on at full brightness.
int	ON_AFTER_RELEASE	当这个wake lock已释放时，拨开了用户界面的计时器所以屏幕停留稍微长。 When this wake lock is released, poke the user activity timer so the screen stays on for a little longer.
int	PARTIAL_WAKE_LOCK	Wake lock以确保CPU运行。 Wake lock that ensures that the CPU is running.
int	SCREEN_BRIGHT_WAKE_LOCK	Wake lock以确保屏幕全亮；键盘背光允许关闭。 Wake lock that ensures that the screen is on at full brightness; the keyboard backlight will be allowed to go off.
int	SCREEN_DIM_WAKE_LOCK	Wake lock以确保屏幕打开（但可以是暗淡的）；键盘背光将允许关闭。 Wake lock that ensures that the screen is on (but may be dimmed); the keyboard backlight will be allowed to go off.

Public Methods
void	goToSleep(long time) 强制设备进入休眠。 Force the device to go to sleep.
boolean	IsScreenOn() 返回屏幕是否当前亮着。 Returns whether the screen is currently on.
PowerManager.WakeLock	newWakeLock(int flags, String tag) 得到一个Wake lock在这个标志参数的级别。 Get a wake lock at the level of the flags parameter.
void	reboot(String reason) 重启设备 Reboot the device.
void	userActivity(long when, boolean noChangeLights) 用户界面发生。 User activity happened.