An alert dialog is a term for a particular type of dialog box that occurs in a graphical user interface. It is also known as an alert box, alert window, or alert popup.

Alerts were designed for two main uses. The first is to inform the user than an operation could not continue or complete due to some insurmountable error. The second is to warn them that the current course of action could be in some way dangerous or detrimental, and to offer the option of not proceeding.

The following tip shows how to show alert dialog boxes in Java ME.

 import javax.microedition.midlet.*;
import javax.microedition.lcdui.*;
public class DisplayAlert extends MIDlet implements CommandListener
{
  private Display display; 
  private Alert alert;
  private Form form; 
  private Command exit; 
  private boolean exitFlag; 
  public DisplayAlert()
  {
    exitFlag = false;
    display = Display.getDisplay(this);
    exit = new Command("Exit", Command.SCREEN, 1);
    form = new Form("Throw Exception");
    form.addCommand(exit);
    form.setCommandListener(this);
  }
  public void startApp()
  {
   display.setCurrent(form);
  }
  public void pauseApp()
  {
  }
  public void destroyApp(boolean unconditional) 
        throws MIDletStateChangeException
  {
    if (unconditional == false)
    {
     throw new MIDletStateChangeException();
    }
  }      
  public void commandAction(Command command, Displayable displayable)
  {
    if (command == exit)
    {
      try
      {
        if (exitFlag == false)
        {
         alert = new Alert("Busy", "Please try again.", 
                           null, AlertType.WARNING); 
         alert.setTimeout(Alert.FOREVER); 
         display.setCurrent(alert, form);
         destroyApp(false);
        }
        else
        {
         destroyApp(true);
         notifyDestroyed();
        }
      }
      catch (MIDletStateChangeException exception)
      {
        exitFlag = true; 
      }
    }
  }
}

 

 

 

 Related Tips