Key Listener

[Slyvr]

This is my first time trying to use KeyListener and I just need it to move an image over 20 px every time I press the right arrow key. After 400px, it should move down to the next line vertically 'playery.' For Some reason it prints out the console output twice. I also just want to make sure my layout for everything is common and acceptable

addKeyListener (
	         new KeyListener() {
	            public void keyPressed(KeyEvent e) {
	            	System.out.println("key pressed");
	            	if (e.getKeyCode() == KeyEvent.VK_RIGHT){
	            		playerx+=20;
	            		System.out.println("playerx: "+playerx);
	            		if (playerx>400){
	            			playery+=20;
	            			playerx=0;
	            		}
	            		repaint();
	            	}
	            }
				public void keyReleased(KeyEvent arg0) {
					System.out.println("key released");
				}
				public void keyTyped(KeyEvent arg0) {
					System.out.println("key typed");
				}
	         }
	);

This is my console output:

key pressed
playerx: 20
key pressed
playerx: 40
key released
key released
key released

For some reason, one key stroke replies with 2.

[Slyvr]

I have code for a basic game I'm building. I haven't used KeyListener before and I need a player image to move over 20 pixels when an arrow key is pressed.

addKeyListener (
    		new KeyListener() {
    			public void keyPressed(KeyEvent p) {
    				System.out.println("key pressed");
    				if ((p.getKeyCode() == KeyEvent.VK_RIGHT)&&(playerx<380)){
    					playerx+=20;
    					System.out.println("playerx: "+playerx);
    					repaint();
    				}
    				if ((p.getKeyCode() == KeyEvent.VK_LEFT)&&(playerx>0)){
    					playerx-=20;
    					System.out.println("playerx: "+playerx);
    					repaint();
    				}
    				if ((p.getKeyCode() == KeyEvent.VK_UP)&&(playery>0)){
    					playery-=20;
    					System.out.println("playerx: "+playerx);
    					repaint();
    				}
    				if ((p.getKeyCode() == KeyEvent.VK_DOWN)&&(playery<400)){
    					playery+=20;
    					System.out.println("playerx: "+playerx);
    					repaint();
    				}
    			}
    			public void keyReleased(KeyEvent r) {
    				System.out.println("key released");
    			}
    			public void keyTyped(KeyEvent t) {
    				System.out.println("key typed");
    			}
    		}
    );

What I get from this with right arrow key is used twice:

key pressed
playerx: 20
key pressed
playerx: 40
key released
key released
key released
key pressed
playerx: 60
key pressed
playerx: 80
key pressed
playerx: 100
key released
key released
key released
key released

What I want:

key pressed
playerx: 40
key released
key pressed
playerx: 60
key released

[mKorbel]

majorities of Listeners works multiplayed, but just last give output to GUI, you can compare that with DocumentListener, ListSelectionListener ...

http://download.oracle.com/javase/tutorial/uiswing/events/index.html

check this one http://download.oracle.com/javase/tutorial/uiswing/misc/keybinding.html

[Slyvr]

majorities of Listeners works multiplayed, but just last give output to GUI, you can compare that with DocumentListener, ListSelectionListener ...

http://download.oracle.com/javase/tutorial/uiswing/events/index.html

check this one http://download.oracle.com/javase/tutorial/uiswing/misc/keybinding.html

Sorry, I didn't get anything out of that :/ What exactly is wrong with my code that makes it exponentially increase its output?

[Ezzaral]

Are you sure you haven't added the listener more than once? Because that is kind of what your output looks like. I don't see anything wrong with your listener code itself.

[Slyvr]

Are you sure you haven't added the listener more than once? Because that is kind of what your output looks like. I don't see anything wrong with your listener code itself.

I'm positive. I'll post the entire program if that helps, but I've looked into almost everything. I just thought it might be something to do with KeyListener itself

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;
import java.awt.image.ImageObserver;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.border.TitledBorder;

class GridsCanvas extends Canvas {
   int width, height;
   int rows;
   int cols;
   int playerx=0, playery=0;
   BufferedImage mob1=null, bg=null;
   ImageObserver observe = null;

   GridsCanvas(int w, int h, int r, int c) {
      setSize(width=w, height=h);
      rows = r;
      cols = c;
   }

   public void paint(Graphics g) {
      int i;
      width = getSize().width;
      height = getSize().height;
      
      try {
		mob1 = ImageIO.read(new File("mob1.png"));
		bg = ImageIO.read(new File("grid.png"));
	} catch (IOException e) {
		e.printStackTrace();
	}
	
      //grid is 20x21
      boolean wall=false;
      int NumofTiles=420;
      int x=0, y=0;

    g.drawImage(bg, 0, 0, observe);
    g.drawImage(mob1, playerx, playery, observe);

    addKeyListener (
	         new KeyListener() {
	            public void keyPressed(KeyEvent p) {
	            	System.out.println("PLAYERX 1: "+playerx);
	            	System.out.println("key pressed");
	            	if ((p.getKeyCode() == KeyEvent.VK_RIGHT)&&(playerx<380)){
	            		playerx+=20;
	            		System.out.println("playerx: "+playerx);
	            	}
	            	else if ((p.getKeyCode() == KeyEvent.VK_LEFT)&&(playerx>0)){
	            		playerx-=20;
	            		System.out.println("playerx: "+playerx);
	            	}
	            	else if ((p.getKeyCode() == KeyEvent.VK_UP)&&(playery>0)){
	            		playery-=20;
	            		System.out.println("playery: "+playery);
	            	}
	            	else if ((p.getKeyCode() == KeyEvent.VK_DOWN)&&(playery<400)){
	            		playery+=20;
	            		System.out.println("playery: "+playery);
	            	}
	            	repaint();
	            	System.out.println("PLAYERX 2: "+playerx);
	            }
				public void keyReleased(KeyEvent r) {
					System.out.println("key released");
				}
				public void keyTyped(KeyEvent t) {
					System.out.println("key typed");
				}
	         }
	);  
   }
}

/** This is the demo class. */
public class Grids extends Frame {
   /* Construct a GfxDemo2 given its title, width and height.
    * Uses a GridBagLayout to make the Canvas resize properly.
    */
	
   Grids(String title, int w, int h, int rows, int cols) {
      setTitle(title);

      // Now create a Canvas and add it to the Frame.
      GridsCanvas xyz = new GridsCanvas(w, h, rows, cols);
      add(xyz);
      setResizable(true);

        addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent e) {
            setVisible(false);
            dispose();
            System.exit(0);
         }
      });

      // Normal end ... pack it up!
      pack();
   }  

   public static void main(String[] a) {
      new Grids("Grid", 500, 500, 20, 20).setVisible(true);
   }
}

EDIT: Ok, so I just added a MouseListener and a counter for number of mouseclicks. It's doubling that as well but it doesn't exponentially increase. It's always two mouse clicks when I'm actually only clicking once.

[Ezzaral]

You are adding the key listener in your paint() method. Every time it gets called, you add another.

[Slyvr]

You are adding the key listener in your paint() method. Every time it gets called, you add another.

Ahhh, thank you :D I cleaned up the code a bit now and trying to figure out how to repaint(); from inside the main class for the keylistener now...

[Ezzaral]

Just move the addListener() code up into the constructor. You can still call repaint() the same way.

edit: You may want to consider using Swing JFrame and JPanel classes instead of Frame and Canvas unless there is a reason you need to stick to older awt classes.

[Slyvr]

Just move the addListener() code up into the constructor. You can still call repaint() the same way.

edit: You may want to consider using Swing JFrame and JPanel classes instead of Frame and Canvas unless there is a reason you need to stick to older awt classes.

Huzzah! It's working perfectly and all the code is completely cleaned up. Thanks for your help. Darwin fish ftw