Blocking the screen saver using J2Me

If your application doesn't demand constant key presses, after a while the screen saver on a J2ME phone will start automatically.

To make sure that the display light is turned on, the setLights method should be called before the screen saver is started and this must be done in a loop since the screen saver is not disabled just interrupted.

BacklightWorkaround.java

import com.nokia.mid.ui.DeviceControl;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

public class BacklightWorkaround extends MIDlet {

private SimpleCanvas canvas;

/**
 * Keeps the backlight on by repeatedly setting
 */
class LightThread extends Thread {
  public void run() {
    while(true){
   
      DeviceControl.setLights(0, 100);     
      try {
        Thread.sleep(5000);
      } catch (InterruptedException ex) {
        ex.printStackTrace();
      }
    }
  }
}

private class SimpleCanvas extends Canvas implements CommandListener{
  private Command exitCmd;
  private MIDlet midlet;

  public SimpleCanvas(MIDlet midlet) {
    this.midlet = midlet;
    exitCmd = new Command("Exit",Command.EXIT, 1);
    addCommand(exitCmd);
    setCommandListener(this);
  }
  public void paint(Graphics g) {   
    g.drawString("Let there be light.", 0, 0, Graphics.LEFT|Graphics.TOP);
  }

  public void commandAction(Command command, Displayable displayable) {
    if(command == exitCmd){
      midlet.notifyDestroyed();
    }
  }
}

public void startApp() {
  if(canvas == null){
    canvas = new SimpleCanvas(this);
    new LightThread().start();
  }

  Display.getDisplay(this).setCurrent(canvas);
}

public void pauseApp() { }

public void destroyApp(boolean unconditional) { }
}