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Android APIs
public class

PowerManager

extends Object
java.lang.Object
   ↳ android.os.PowerManager

Class Overview

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

Device battery life will be significantly affected by the use of this API. Do not acquire WakeLocks unless you really need them, use the minimum levels possible, and be sure to release it as soon as you can.

You can obtain an instance of this class by calling Context.getSystemService().

The primary API you'll use is newWakeLock(). This will create a PowerManager.WakeLock object. You can then use methods on this object to control the power state of the device. In practice it's quite simple: 

PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
 PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.SCREEN_DIM_WAKE_LOCK, "My Tag");
 wl.acquire();
   ..screen will stay on during this section..
 wl.release();

The following flags are defined, with varying effects on system power. These flags are mutually exclusive - you may only specify one of them.

Flag Value CPU Screen Keyboard
PARTIAL_WAKE_LOCK On* Off Off
SCREEN_DIM_WAKE_LOCK On Dim Off
SCREEN_BRIGHT_WAKE_LOCK On Bright Off
FULL_WAKE_LOCK On Bright Bright

*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.

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 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 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.
Any application using a WakeLock must request the android.permission.WAKE_LOCK permission in an <uses-permission> element of the application's manifest.

Summary

Nested Classes
class PowerManager.WakeLock Class lets you say that you need to have the device on. 
Constants
int ACQUIRE_CAUSES_WAKEUP 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 that ensures that the screen and keyboard are on at full brightness.
int ON_AFTER_RELEASE 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 that ensures that the CPU is running.
int SCREEN_BRIGHT_WAKE_LOCK This constant is deprecated. Most applications should use FLAG_KEEP_SCREEN_ON instead of this type of wake lock, as it will be correctly managed by the platform as the user moves between applications and doesn't require a special permission. 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 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)
Force the device to go to sleep.
boolean isScreenOn()
Returns whether the screen is currently on.
PowerManager.WakeLock newWakeLock(int flags, String tag)
Get a wake lock at the level of the flags parameter.
void reboot(String reason)
Reboot the device.
void userActivity(long when, boolean noChangeLights)
User activity happened.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int ACQUIRE_CAUSES_WAKEUP

Since: API Level 1

Normally wake locks don't actually wake the device, they just cause it to remain on once it's already on. Think of the video player app as the normal behavior. Notifications that pop up and want the device to be on are the exception; use this flag to be like them.

Does not work with PARTIAL_WAKE_LOCKs.

Constant Value: 268435456 (0x10000000)

public static final int FULL_WAKE_LOCK

Since: API Level 1

Wake lock that ensures that the screen and keyboard are on at full brightness.

Most applications should strongly consider using FLAG_KEEP_SCREEN_ON. This window flag will be correctly managed by the platform as the user moves between applications and doesn't require a special permission.

Constant Value: 26 (0x0000001a)

public static final int ON_AFTER_RELEASE

Since: API Level 1

When this wake lock is released, poke the user activity timer so the screen stays on for a little longer.

Will not turn the screen on if it is not already on. See ACQUIRE_CAUSES_WAKEUP if you want that.

Does not work with PARTIAL_WAKE_LOCKs.

Constant Value: 536870912 (0x20000000)

public static final int PARTIAL_WAKE_LOCK

Since: API Level 1

Wake lock that ensures that the CPU is running. The screen might not be on.

Constant Value: 1 (0x00000001)

public static final int SCREEN_BRIGHT_WAKE_LOCK

Since: API Level 1

This constant is deprecated.
Most applications should use FLAG_KEEP_SCREEN_ON instead of this type of wake lock, as it will be correctly managed by the platform as the user moves between applications and doesn't require a special permission. Wake lock that ensures that the screen is on at full brightness; the keyboard backlight will be allowed to go off.

Constant Value: 10 (0x0000000a)

public static final int SCREEN_DIM_WAKE_LOCK

Since: API Level 1

Wake lock that ensures that the screen is on (but may be dimmed); the keyboard backlight will be allowed to go off.

Constant Value: 6 (0x00000006)

Public Methods

public void goToSleep (long time)

Since: API Level 1

Force the device to go to sleep. Overrides all the wake locks that are held.

Parameters
time is used to order this correctly with the wake lock calls. The time should be in the SystemClock.uptimeMillis() time base.

public boolean isScreenOn ()

Since: API Level 7

Returns whether the screen is currently on. The screen could be bright or dim. 

PowerManager pm = (PowerManager) getSystemService(Context.POWER_SERVICE);
 boolean isScreenOn = pm.isScreenOn();

Returns
  • whether the screen is on (bright or dim).

public PowerManager.WakeLock newWakeLock (int flags, String tag)

Since: API Level 1

Get a wake lock at the level of the flags parameter. Call acquire() on the object to acquire the wake lock, and release() when you are done. 

PowerManager pm = (PowerManager)mContext.getSystemService(
                                          Context.POWER_SERVICE);
PowerManager.WakeLock wl = pm.newWakeLock(
                                      PowerManager.SCREEN_DIM_WAKE_LOCK
                                      | PowerManager.ON_AFTER_RELEASE,
                                      TAG);
wl.acquire();
 // ...
wl.release();

If using this to keep the screen on, you should strongly consider using FLAG_KEEP_SCREEN_ON instead. This window flag will be correctly managed by the platform as the user moves between applications and doesn't require a special permission.

Parameters
flags Combination of flag values defining the requested behavior of the WakeLock.
tag Your class name (or other tag) for debugging purposes.
See Also

public void reboot (String reason)

Since: API Level 8

Reboot the device. Will not return if the reboot is successful. Requires the REBOOT permission.

Parameters
reason code to pass to the kernel (e.g., "recovery") to request special boot modes, or null.

public void userActivity (long when, boolean noChangeLights)

Since: API Level 1

User activity happened.

Turns the device from whatever state it's in to full on, and resets the auto-off timer.

Parameters
when is used to order this correctly with the wake lock calls. This time should be in the SystemClock.uptimeMillis() time base.
noChangeLights should be true if you don't want the lights to turn on because of this event. This is set when the power key goes down. We want the device to stay on while the button is down, but we're about to turn off. Otherwise the lights flash on and then off and it looks weird.