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Android APIs
public final 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 PowerManager.WakeLock s unless you really need them, use the minimum levels possible, and be sure to release them as soon as possible.

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 the wake lock 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 wake lock levels are defined, with varying effects on system power. These levels 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 wake lock, the CPU will continue to run, regardless of any display timeouts or the state of the screen and even after the user presses the power button. In all other wake locks, 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 A wake lock is a mechanism to indicate that your application needs to have the device stay on. 
Constants
int ACQUIRE_CAUSES_WAKEUP Wake lock flag: Turn the screen on when the wake lock is acquired.
int FULL_WAKE_LOCK This constant was deprecated in API level 17. 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.
int ON_AFTER_RELEASE Wake lock flag: 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 level: Ensures that the CPU is running; the screen and keyboard backlight will be allowed to go off.
int SCREEN_BRIGHT_WAKE_LOCK This constant was deprecated in API level 13. 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.
int SCREEN_DIM_WAKE_LOCK This constant was deprecated in API level 17. 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.
Public Methods
void goToSleep (long time)
Forces the device to go to sleep.
boolean isInteractive ()
Returns true if the device is in an interactive state.
boolean isScreenOn ()
This method was deprecated in API level 20. Use isInteractive() instead.
PowerManager.WakeLock newWakeLock (int levelAndFlags, String tag)
Creates a new wake lock with the specified level and flags.
void reboot ( String reason)
Reboot the device.
void userActivity (long when, boolean noChangeLights)
Notifies the power manager that user activity happened.
void wakeUp (long time)
Forces the device to wake up from sleep.
[Expand]
Inherited Methods
From class java.lang.Object

Constants

public static final int ACQUIRE_CAUSES_WAKEUP

Added in API level 1

Wake lock flag: Turn the screen on when the wake lock is acquired.

Normally wake locks don't actually wake the device, they just cause the screen to remain on once it's already on. Think of the video player application 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.

Cannot be used with PARTIAL_WAKE_LOCK .

Constant Value: 268435456 (0x10000000)

public static final int FULL_WAKE_LOCK

Added in API level 1

This constant was deprecated in API level 17.
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 level: Ensures that the screen and keyboard backlight are on at full brightness.

If the user presses the power button, then the FULL_WAKE_LOCK will be implicitly released by the system, causing both the screen and the CPU to be turned off. Contrast with PARTIAL_WAKE_LOCK .

Constant Value: 26 (0x0000001a)

public static final int ON_AFTER_RELEASE

Added in API level 1

Wake lock flag: 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.

Cannot be used with PARTIAL_WAKE_LOCK .

Constant Value: 536870912 (0x20000000)

public static final int PARTIAL_WAKE_LOCK

Added in API level 1

Wake lock level: Ensures that the CPU is running; the screen and keyboard backlight will be allowed to go off.

If the user presses the power button, then the screen will be turned off but the CPU will be kept on until all partial wake locks have been released.

Constant Value: 1 (0x00000001)

public static final int SCREEN_BRIGHT_WAKE_LOCK

Added in API level 1

This constant was deprecated in API level 13.
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 level: Ensures that the screen is on at full brightness; the keyboard backlight will be allowed to go off.

If the user presses the power button, then the SCREEN_BRIGHT_WAKE_LOCK will be implicitly released by the system, causing both the screen and the CPU to be turned off. Contrast with PARTIAL_WAKE_LOCK .

Constant Value: 10 (0x0000000a)

public static final int SCREEN_DIM_WAKE_LOCK

Added in API level 1

This constant was deprecated in API level 17.
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 level: Ensures that the screen is on (but may be dimmed); the keyboard backlight will be allowed to go off.

If the user presses the power button, then the SCREEN_DIM_WAKE_LOCK will be implicitly released by the system, causing both the screen and the CPU to be turned off. Contrast with PARTIAL_WAKE_LOCK .

Constant Value: 6 (0x00000006)

Public Methods

public void goToSleep (long time)

Added in API level 1

Forces the device to go to sleep.

Overrides all the wake locks that are held. This is what happens when the power key is pressed to turn off the screen.

Requires the DEVICE_POWER permission.

Parameters
time The time when the request to go to sleep was issued, in the uptimeMillis() time base. This timestamp is used to correctly order the go to sleep request with other power management functions. It should be set to the timestamp of the input event that caused the request to go to sleep.
See Also

public boolean isInteractive ()

Returns true if the device is in an interactive state.

When this method returns true, the device is awake and ready to interact with the user (although this is not a guarantee that the user is actively interacting with the device just this moment). The main screen is usually turned on while in this state. Certain features, such as the proximity sensor, may temporarily turn off the screen while still leaving the device in an interactive state. Note in particular that the device is still considered to be interactive while dreaming (since dreams can be interactive) but not when it is dozing or asleep.

When this method returns false, the device is dozing or asleep and must be awoken before it will become ready to interact with the user again. The main screen is usually turned off while in this state. Certain features, such as "ambient mode" may cause the main screen to remain on (albeit in a low power state) to display system-provided content while the device dozes.

The system will send a screen on or screen off broadcast whenever the interactive state of the device changes. For historical reasons, the names of these broadcasts refer to the power state of the screen but they are actually sent in response to changes in the overall interactive state of the device, as described by this method.

Services may use the non-interactive state as a hint to conserve power since the user is not present.

Returns
  • True if the device is in an interactive state.
See Also

public boolean isScreenOn ()

Added in API level 7

This method was deprecated in API level 20.
Use isInteractive() instead.

Returns true if the device is in an interactive state.

For historical reasons, the name of this method refers to the power state of the screen but it actually describes the overall interactive state of the device. This method has been replaced by isInteractive() .

The value returned by this method only indicates whether the device is in an interactive state which may have nothing to do with the screen being on or off. To determine the actual state of the screen, use getState() .

Returns
  • True if the device is in an interactive state.

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

Added in API level 1

Creates a new wake lock with the specified level and flags.

The levelAndFlags parameter specifies a wake lock level and optional flags combined using the logical OR operator.

The wake lock levels are: PARTIAL_WAKE_LOCK , FULL_WAKE_LOCK , SCREEN_DIM_WAKE_LOCK and SCREEN_BRIGHT_WAKE_LOCK . Exactly one wake lock level must be specified as part of the levelAndFlags parameter.

The wake lock flags are: ACQUIRE_CAUSES_WAKEUP and ON_AFTER_RELEASE . Multiple flags can be combined as part of the levelAndFlags parameters.

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();
 // ... do work...
 wl.release();

Although a wake lock can be created without special permissions, the WAKE_LOCK permission is required to actually acquire or release the wake lock that is returned.

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
levelAndFlags Combination of wake lock level and 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)

Added in 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)

Added in API level 1

Notifies the power manager that user activity happened.

Resets the auto-off timer and brightens the screen if the device is not asleep. This is what happens normally when a key or the touch screen is pressed or when some other user activity occurs. This method does not wake up the device if it has been put to sleep.

Requires the DEVICE_POWER permission.

Parameters
when The time of the user activity, in the uptimeMillis() time base. This timestamp is used to correctly order the user activity request with other power management functions. It should be set to the timestamp of the input event that caused the user activity.
noChangeLights If true, does not cause the keyboard backlight to turn on because of this event. This is set when the power key is pressed. We want the device to stay on while the button is down, but we're about to turn off the screen so we don't want the keyboard backlight to turn on again. Otherwise the lights flash on and then off and it looks weird.
See Also

public void wakeUp (long time)

Forces the device to wake up from sleep.

If the device is currently asleep, wakes it up, otherwise does nothing. This is what happens when the power key is pressed to turn on the screen.

Requires the DEVICE_POWER permission.

Parameters
time The time when the request to wake up was issued, in the uptimeMillis() time base. This timestamp is used to correctly order the wake up request with other power management functions. It should be set to the timestamp of the input event that caused the request to wake up.
See Also