Categories: Java ME | MIDP 2.0 | Code Examples | Hardware | S60 3rd Edition, Feature Pack 1

This page was last modified 20:30, 9 October 2008.

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Overview

This snippet demonstrates how to flash the backlight of the device for a specified duration. In practice, the MIDlet constructs a menu item through which the user can flash the backlight.

Source

Flashing the backlight can be implemented as follows:

// Flash the backlight for 5 seconds
Display.getDisplay(this).flashBacklight(5000);

Here is a complete example:

import javax.microedition.lcdui.Command;
import javax.microedition.lcdui.CommandListener;
import javax.microedition.lcdui.Display;
import javax.microedition.lcdui.Displayable;
import javax.microedition.lcdui.Form;
import javax.microedition.midlet.MIDlet;

public class ExampleMIDlet extends MIDlet implements CommandListener {
    private Command flashCommand;
    private Command exitCommand;
    private Form mainForm;
 
    /**
     * Constructor. Constructs the object and initializes displayables.
     */
    public ExampleMIDlet() {
        mainForm = new Form("ExampleMIDlet");
        
        flashCommand = new Command("Flash", Command.SCREEN, 0);
        mainForm.addCommand(flashCommand);
        
        exitCommand = new Command("Exit", Command.EXIT, 0);
        mainForm.addCommand(exitCommand);
        
        mainForm.setCommandListener(this);
    }
    
    /**
     * Called when the MIDlet is started.
     */
    public void startApp() {
        Display.getDisplay(this).setCurrent(mainForm);
    }
    
    // Other inherited methods omitted for brevity
    // ...
    
    /**
     * From CommandListener.
     * Called by the system to indicate that a command has been invoked on a
     * particular displayable.
     * @param command the command that was invoked
     * @param displayable the displayable where the command was invoked
     */
    public void commandAction(Command command, Displayable displayable) {
        if (command == flashCommand) {
            // Flash the backlight for 5 seconds
            boolean flashAllowed = Display.getDisplay(this).flashBacklight(5000);
            if (!flashAllowed) {
                // TODO: Flashing is not allowed. Inform the user.
            }
        } else if (command == exitCommand) {
            // Exit the MIDlet
            destroyApp(true);
            notifyDestroyed();
        }
    }

Postconditions

If the user selects the Flash menu item, the backlight is flashed for 5 seconds.