Screen saver

You can control the device screen saver with the Nokia UI API. By default, the screen saver starts automatically if the device user does not press any key within a certain timeframe (set to 5 seconds by default on Symbian devices). You can prevent this by keeping the screen backlight active with the Nokia UI API. The Nokia UI API provides two methods for controlling the screen backlight:

If your target device supports Nokia UI API 1.4 or newer, use the DeviceControl.resetUserInactivityTime method, since it does not change the screen brightness.

Note: Forcing the display to be constantly switched on consumes more battery. To take this into account, program the MIDlet to disable the screen saver only when on the foreground, for example.

DeviceControl.setLights

The DeviceControl.setLights method activates and deactivates the screen backlight on the device. When used to activate the backlight, the method switches the backlight on and resets the user inactivity timers on the device. If called in a loop, the backlight activation prevents the screen saver from starting.

Using the DeviceControl.setLights method to prevent the screen saver from starting is supported since Series 40 1st Edition and S60 3rd Edition, Feature Pack 1.

Note: Using the DeviceControl.setLights method overrides the device's ambient light sensor settings and can thus change the screen brightness.

Note: Resetting the user inactivity timers also prevents the automatic keypad lock from being activated.

The following example shows how to use the DeviceControl.setLights method to prevent the screen saver from starting. The screen saver timeout value is configurable, but it cannot be accessed using Java, so a hard-coded value is used in the example loop.

class DisableScreenSaver extends Thread {
  public void run() {
    while(true) {
      DeviceControl.setLights(0, 100);
      try {
        Thread.sleep(4000);   // minimum screen saver timeout in UI is 5 seconds
      } catch (InterruptedException e) {
      }
    }
  }
}

public class MyMidlet extends MIDlet {
  public void startApp() {
    new DisableScreenSaver().start();
    ...
  }
  ...
}

DeviceControl.resetUserInactivityTime

The DeviceControl.resetUserInactivityTime method resets all the user inactivity timers on the device. If called in a loop, resetting the user inactivity timers prevents the screen saver from starting.

The DeviceControl.resetUserInactivityTime method is supported since Nokia UI API 1.4 on Java Runtime 2.1 for Symbian and newer.

To determine whether the device supports the DeviceControl.resetUserInactivityTime method, use the com.nokia.mid.ui.screensaverprevention system property.

Note: Using the DeviceControl.resetUserInactivityTime method does not change the screen brightness.

Note: Resetting the user inactivity timers also prevents the automatic keypad lock from being activated.

The following example shows how to use the DeviceControl.resetUserInactivityTime method to prevent the screen saver from starting. The screen saver timeout value is configurable, but it cannot be accessed using Java, so a hard-coded value is used in the example loop.

class DisableScreenSaver extends Thread {
  public void run() {
    while(true) {
      DeviceControl.resetUserInactivityTime();   // reseting all user inactivity timers
      try {
        Thread.sleep(4000);   // minimum screen saver timeout in UI is 5 seconds
      } catch (InterruptedException e) {
      }
    }
  }
}

public class MyMidlet extends MIDlet {
  public void startApp() {
    new DisableScreenSaver().start();
    ...
  }
  ...
}
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