keyListener

[r bal]

For some reason my key listeners don't even register anything. Even if I had println statements in it, they do not come up.

In my class with the main method, I have have extended JFrame. In my constructor for this class I have:

addKeyListener(myBoard); Where myBoard has been created as an object of Board class.

Then in Board class I have my keyListeners. The method implements KeyListener. And I have the three methods keyPressed, keyTyped, and keyReleased.

public void keyTyped(KeyEvent keyEvent) {
int k = keyEvent.getKeyCode();
if (k == KeyEvent.VK_DOWN) {
System.out.println("down working");
}
else if (k == KeyEvent.VK_UP) {
System.out.println("up working");
}
}

public void keyPressed(KeyEvent keyEvent) {
}

public void keyReleased(KeyEvent keyEvent) {
}


Then in my constructor for this class I have:
addKeyListener(this);

Any clue as to why my keyListener is not working???

[Stuart Gray]

Put a System.out.println call in those three methods before any of the if statements. They should be being called.

[Michael Dunn]

from the KeyEvent api

"For key pressed and key released events, the getKeyCode method returns the
event's keyCode. For key typed events, the getKeyCode method always returns
VK_UNDEFINED."

change to keyPressed/Released and it should work OK

[Stuart Gray]

Yep, that is where I was heading. I figured the methods must be being called, so probably the if statements were not evaluating to true. Didn't have the API docs handy though.

r bal sometimes it can be very useful to add a few extra println calls to your code to determine what is happening. By putting a println at the top of the method, you can tell whether or not the method is being called at all. Its a very useful debugging technique sometimes.

public void keyTyped(KeyEvent keyEvent) {
   [B]System.out.println("Inside keyTyped method");[/B]
   int k = keyEvent.getKeyCode();
   if (k == KeyEvent.VK_DOWN) {
      System.out.println("down working");
   } else if (k == KeyEvent.VK_UP) {
      System.out.println("up working");
   }
}

[ May 13, 2005: Message edited by: Stuart Gray ]

[r bal]

thanks for all the advice....

but unfortunately, the methods aren't even being read. Ie. I put println statements in all the 3 methods before the if statements, and still nothing happened.

i guess i'll keep on with the trial and error.

[Michael Dunn]

it could be what you're adding the listener to.

here's what I think is a reconstruction of your description,
it works OK adding it directly to the frame, and also to the panel,
if the indicated line is set.

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Testing extends JFrame
{
  public Testing()
  {
    setSize(200,200);
    setLocation(400,300);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    Board myBoard = new Board();
      //addKeyListener(myBoard);
      //or
      JPanel jp = new JPanel();
      jp.setFocusable(true);//must have this for it to work with a JPanel
      jp.addKeyListener(myBoard);
      getContentPane().add(jp);
  }
  public static void main(String[] args){new Testing().setVisible(true);}
}
class Board implements KeyListener
{
  public void keyPressed(KeyEvent keyEvent)
  {
    System.out.println("Pressed");
  }
  public void keyTyped(KeyEvent keyEvent)
  {
    System.out.println("Typed");
  }
  public void keyReleased(KeyEvent keyEvent)
  {
    System.out.println("Released");
  }
}

[r bal]

The option you had that was commented out...was the one I orginally had.

I tried the other option using the JPanel, but still no success.

I have tried absolutely everything I can think of.

This has me stumped.

[Stuart Gray]

A thought - when you call addKeyListener(myboard), has myboard already been initialised at this point? The reason I ask is because if it is null the addKeyListener won't work - but no error message will be thrown either! Basically you should have a line like this somewhere before you try to add the KeyListener:

Board myboard = new Board();

[r bal]

yes, i have that line of code before I add the keyListener.

I just can't figure it out...everything I need seems to be there and in the right place.

Is there any other way to go about adding keyListeners using different methods or different classes?

[Stuart Gray]

Maybe you can post the full code if it is relatively short?