KeyListener woes

[Dan Kottas]

I would like this program to move a picture around the screen as someone presses the arrow keys. The problem is, I can't get the KeyListener to listen to keys while it's looping in my page flipping loop.

There is a MouseListener attached to my window that works great. However, the KeyListener I added doesn't do a thing.

I've tried a number of different things and most of it is commented out. So, I apologize for the mess. If anyone could help me out I would greatly appreciate it.

 
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.image.BufferStrategy;
 
public class Viewer extends Frame
implements KeyListener/*, MouseListener*/
{
private Image image;
private final int LEFT = 0;
private final int RIGHT = 1;
private final int UP = 2;
private final int DOWN = 3;
int frames=0;
 
// Determine if page flipping is supported
GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
GraphicsDevice gd = ge.getDefaultScreenDevice();
GraphicsConfiguration gc = gd.getDefaultConfiguration();
BufferCapabilities bufCap = gc.getBufferCapabilities();
boolean page = bufCap.isPageFlipping();
 
public void doMovement(int i)
{
switch(i){
case LEFT:
System.out.println("left");
break;
case RIGHT:
System.out.println("right");
break;
case DOWN:
System.out.println("down");
break;
case UP:
System.out.println("up");
break;
default:
System.out.println("oops");
break;
}
}
 
public Viewer() {
/*addKeyListener(this);*/
/*addMouseListener(this);*/
//Check for supported page flipping
if (page) {
    // Page flipping is supported
    System.out.println("Page flipping is a go.");
} else {
    // Page flipping is not supported
        System.out.println("Page flipping is a no-go.");
}
Frame frame = new Frame(gd.getDefaultConfiguration());
    Window win = new Window(frame);
 
    win.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent evt) {
            // Exit full-screen mode
            GraphicsDevice gd = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice();
            gd.setFullScreenWindow(null);
        }
    });
   //win.addKeyListener(this);
/*
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*/
    win.addKeyListener(new KeyAdapter() {
public synchronized void keyPressed(KeyEvent e){
System.out.println("I'm here");
switch(e.getKeyCode()){
case KeyEvent.VK_LEFT: doMovement(LEFT);
break;
case KeyEvent.VK_RIGHT: doMovement(RIGHT);
break;
case KeyEvent.VK_DOWN: doMovement(DOWN);
break;
case KeyEvent.VK_UP: doMovement(UP);
break;
default: System.out.println("oops1");
break;
}
e.consume();
}
});
try {
// Enter full-screen mode
gd.setFullScreenWindow(win);
win.requestFocus();
 
 
 
        // Create the back buffer
        int numBuffers = 2;  // Includes front buffer
        win.createBufferStrategy(numBuffers);
 
        // Determine the state of a back buffer after it has been displayed on the screen.
        // This information is used to optimize performance. For example, if your application
        // needs to initialize a back buffer with a background color, there is
        // no need to do so if the flip contents is BACKGROUND.
        BufferStrategy strategy = win.getBufferStrategy();
        bufCap = strategy.getCapabilities();
        BufferCapabilities.FlipContents flipContents = bufCap.getFlipContents();
        if (flipContents.equals(BufferCapabilities.FlipContents.UNDEFINED)) {
            System.out.println("1");
        } else if (flipContents.equals(BufferCapabilities.FlipContents.BACKGROUND)) {
            System.out.println("2");
        } else if (flipContents.equals(BufferCapabilities.FlipContents.PRIOR)) {
            System.out.println("3");
        } else if (flipContents.equals(BufferCapabilities.FlipContents.COPIED)) {
System.out.println("4");
            // The contents is identical to the contents just pushed to the
            // front buffer after a flip
        }
        // Draw loop
        while (true) {
            // Get screen size
            int screenWidth = win.getWidth();
            int screenHeight = win.getHeight();
 
            // Get graphics context for drawing to the window
            Graphics g = strategy.getDrawGraphics();
            if (!flipContents.equals(BufferCapabilities.FlipContents.BACKGROUND)) {
/*if(e.getKeyCode()==KeyEvent.VK_LEFT){
System.out.println("worked");
}*/
                // Clear background
                g.setColor(Color.white);
                g.fillRect(0, 0, screenWidth, screenHeight);
g.setColor(Color.black);
       g.fillRect(0,0,1280,1024);
       Toolkit toolkit = Toolkit.getDefaultToolkit();
image = toolkit.getImage("nebraska.jpg");
MediaTracker mediaTracker = new MediaTracker(this);
mediaTracker.addImage(image, 0);
try
{
mediaTracker.waitForID(0);
}
catch (InterruptedException ie)
{
System.err.println(ie);
System.exit(1);
}
g.drawImage(image, win.getWidth()/2-image.getWidth(null)/2, win.getHeight()/2-image.getHeight(null)/2, null);
 }
        frames++;
String s = "frame"+frames;
g.setColor(Color.red);
 g.drawString(s,20,20);
 // Draw shapes and images...
          // Done drawing
            g.dispose();
            // Flip the back buffer to the screen
            //System.out.println("Bout to flip");
            strategy.show();
            //System.out.println("Fliptated!");
        }
    } catch (Throwable e) {
        // Process exception...
    } finally {
        gd.setFullScreenWindow(null);
    }
/*
Toolkit toolkit = Toolkit.getDefaultToolkit();
image = toolkit.getImage("nebraska.jpg");
MediaTracker mediaTracker = new MediaTracker(this);
mediaTracker.addImage(image, 0);
try
{
mediaTracker.waitForID(0);
}
catch (InterruptedException ie)
{
System.err.println(ie);
System.exit(1);
}
addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
});
setSize(800, 600);
setTitle("The Game");
show();*/
}
 
/*public void paint(Graphics graphics) {
graphics.drawImage(image, 400-image.getWidth(null)/2, 300-image.getHeight(null)/2, null);
}*/
 
 
public void keyReleased(KeyEvent e) {}
public void keyTyped(KeyEvent e) {}
public synchronized void keyPressed(KeyEvent e) {
System.out.println("Holy crap this is stupid.");
}
 
/*public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mousePressed(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
public void mouseClicked(MouseEvent e) {}*/
 
public static void main(String[] args) {
new Viewer();
}
}

Sorry to post such a big chunk of code,
Dan

[ EJFH: Added code tags. ]
[ April 26, 2005: Message edited by: Ernest Friedman-Hill ]

[Stuart Gray]

So what is the output of the code? When you press a key nothing happens? You don't see the println messages on the screen?

[Ernest Friedman-Hill]

Hi,

Welcome to JavaRanch!

Events are handled in the same thread that does screen painting. You can't loop forever in the painting method, or events will never get handled -- as you've observed.

So what you must do to do animation is create a separate thread which loops and calls repaint() periodically. Then override paint() (or paintComponent(), in a Swing application) and in that method, draw the screen once based on the values of various member variables. In your event handlers, manipulate those member variables. The end result is that periodically, the screen is repainted in a different state.

For examples of this architecture, check out the "demos" directory in your JDK distribution -- there are a large number of examples.

[Dan Kottas]

Originally posted by Stuart Gray:
So what is the output of the code? When you press a key nothing happens? You don't see the println messages on the screen?

When I run the program it displays the picture in the center of the screen with a black background and counts the frames in the upper left corner. When I press a key nothing happens. No println or anything. The strange part is that when I left-click the mouse, it exits the program like it's supposed to. I do get the println at the beginning of the program that says "Page flipping is a go."

-Dan

[Dan Kottas]

Originally posted by Ernest Friedman-Hill:
Hi,

Welcome to JavaRanch!

Events are handled in the same thread that does screen painting. You can't loop forever in the painting method, or events will never get handled -- as you've observed.

Thank you very much for your help! I'll try this out and see if it works for me. Two things, though, that I'm still not grasping. (1)Why is it that the MouseEvent still gets handled inside of the loop, but the KeyEvent does not? (2)When I comment out the loop, it doesn't display the picture at all. I assume it's flipping to a page that hasn't been drawn on and then quits, but how do I preserve the image on screen? I thought it was the strategy.show() function that was responsible for flipping pages, but apparently not. (Obviously I don't fully understand the page-flipping yet.)
[ April 26, 2005: Message edited by: Dan Kottas ]

[Ernest Friedman-Hill]

I added UBB CODE tags to your first post to make the code easier to see. I'm afraid my reply is offbase -- it doesn't explain what you're seeing at all. IN fact, you're not hogging the event thread, so I don't see why you shouldn't get KeyEvents. I've never worked with the fullscreen mode, so maybe there's a trick here.

I'm going to move this thread to our Swing/AWT forum, where maybe somebody knowledgeable like Gregg will have a look.

[Dan Kottas]

I can't thank you enough for helping me with all of this! I hope someone can help ease my perplexity. I haven't done anything with fullscreen before either so I suppose that could be it.

-Dan

[Michael Dunn]

I changed from a window to an undecorated Frame (Window/JWindow is a pain when
used in conjunction with focus/key listeners)

the code in doMovement() is now processed, but I don't know if using a frame
will affect anything else you're trying to do

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.image.BufferStrategy;
 
class Viewer extends Frame
{
  private Image image;
  private final int LEFT    = 0;
  private final int RIGHT   = 1;
  private final int UP    = 2;
  private final int DOWN    = 3;
  int frames=0;
  GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
  GraphicsDevice gd = ge.getDefaultScreenDevice();
  GraphicsConfiguration gc = gd.getDefaultConfiguration();
  BufferCapabilities bufCap = gc.getBufferCapabilities();
  boolean page = bufCap.isPageFlipping();
  public void doMovement(int i)
  {
    switch(i){
      case LEFT:
        System.out.println("left");
        break;
      case RIGHT:
        System.out.println("right");
        break;
      case DOWN:
        System.out.println("down");
        break;
      case UP:
        System.out.println("up");
        break;
      default:
        System.out.println("oops");
        break;
    }
  }
  public Viewer()
   {
    if (page) System.out.println("Page flipping is a go.");
    else System.out.println("Page flipping is a no-go.");
    Frame frame = new Frame(gd.getDefaultConfiguration());
    frame.setUndecorated(true);//<------------------
    frame.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent evt) {
            GraphicsDevice gd = GraphicsEnvironment.getLocalGraphicsEnvironment().getDefaultScreenDevice();
            gd.setFullScreenWindow(null);
            System.exit(0);}});//close app
    frame.addKeyListener(new KeyAdapter() {
      public void keyPressed(KeyEvent e){
        System.out.println("I'm here");
          switch(e.getKeyCode()){
            case KeyEvent.VK_LEFT: doMovement(LEFT);
              break;
            case KeyEvent.VK_RIGHT: doMovement(RIGHT);
              break;
            case KeyEvent.VK_DOWN: doMovement(DOWN);
              break;
            case KeyEvent.VK_UP: doMovement(UP);
              break;
            default: System.out.println("oops1");
              break;
         }
        e.consume();}});
    try
    {
      gd.setFullScreenWindow(frame);
      frame.requestFocus();
      int numBuffers = 2;
      frame.createBufferStrategy(numBuffers);
      BufferStrategy strategy = frame.getBufferStrategy();
      bufCap = strategy.getCapabilities();
      BufferCapabilities.FlipContents flipContents = bufCap.getFlipContents();
      if (flipContents.equals(BufferCapabilities.FlipContents.UNDEFINED)) System.out.println("1");
      else if (flipContents.equals(BufferCapabilities.FlipContents.BACKGROUND)) System.out.println("2");
      else if (flipContents.equals(BufferCapabilities.FlipContents.PRIOR)) System.out.println("3");
      else if (flipContents.equals(BufferCapabilities.FlipContents.COPIED)) System.out.println("4");
      while (true)
      {
        int screenWidth = frame.getWidth();
        int screenHeight = frame.getHeight();
        Graphics g = strategy.getDrawGraphics();
        if (!flipContents.equals(BufferCapabilities.FlipContents.BACKGROUND))
        {
          g.setColor(Color.white);
          g.fillRect(0, 0, screenWidth, screenHeight);
          g.setColor(Color.black);
          g.fillRect(0,0,1280,1024);
          Toolkit toolkit = Toolkit.getDefaultToolkit();
          image = toolkit.getImage("nebraska.jpg");
          MediaTracker mediaTracker = new MediaTracker(this);
          mediaTracker.addImage(image, 0);
          try
          {
            mediaTracker.waitForID(0);
          }
          catch (InterruptedException ie)
          {
            System.err.println(ie);
            System.exit(1);
          }
          g.drawImage(image, frame.getWidth()/2-image.getWidth(null)/2, frame.getHeight()/2-image.getHeight(null)/2, null);
        }
        frames++;
        String s = "frame"+frames;
        g.setColor(Color.red);
        g.drawString(s,20,20);
        g.dispose();
        strategy.show();
      }
    }
    catch (Throwable e) {}
    finally{gd.setFullScreenWindow(null);}
  }
  public static void main(String[] args){new Viewer();}
}

[Craig Wood]

About the KeyEvents -
The Viewer class implements KeyListener and provides the required methods but is never
referred to or used as a Frame; you could just as well remove 'extends Frame' from the class
declaration (and, if so, 'implements KeyListener' too, by necessity).

A new Frame is instantiated inside Viewer and added to a Window, this new Frame is not
registered with a KeyListener and so may not respond to KeyEvents. Its enclosing Window is
registered with a KeyListener (but its child Frame may be consuming the KeyEvents). If you
will register the new Frame (instead of win) with both the KeyListener and MouseListener as
Michael did they should work. Or, you could use the enclosing class Frame in lieu of the new
Frame: remove all 'frame' instance variable references so the methods will be called on the
enclosing class (a Frame by extension).

Here's one way to set up an animation in AWT. Single left mouse click starts and stops the
animation. Double click closes the Frame.

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.awt.image.BufferStrategy;
 
public class Viewer extends Frame implements Runnable {
    private Image image;
    private final int LEFT  = 0;
    private final int RIGHT = 1;
    private final int UP    = 2;
    private final int DOWN  = 3;
    private final int DELAY = 500;
    int frames = 0;
    String s;
    Thread animator;
    boolean animate;
 
    public void doMovement(int i)
    {
        switch(i){
            case LEFT:
                System.out.println("left");
                break;
            case RIGHT:
                System.out.println("right");
                break;
            case DOWN:
                System.out.println("down");
                break;
            case UP:
                System.out.println("up");
                break;
            default:
                System.out.println("oops");
                break;
        }
    }
 
    public Viewer() {
        s = "hello world";
        animate = false;
        loadImage();                    // only need to load image once
        addWindowListener(new WindowAdapter() {      // added to Viewer
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        setSize(400,400);
        setLocationRelativeTo(null);
        setVisible(true);
 
        addMouseListener(new MouseAdapter() {        // added to enclosing class
            public void mousePressed(MouseEvent evt) {
               if(evt.getClickCount() > 1)
                   System.exit(0);
               else if(animate)
                   stop();
               else
                   start();
            }
        });
 
        addKeyListener(new KeyAdapter() {            // added to enclosing Frame
            public synchronized void keyPressed(KeyEvent e){
                System.out.println("I'm here");
                switch(e.getKeyCode()){
                    case KeyEvent.VK_LEFT: doMovement(LEFT);
                        break;
                    case KeyEvent.VK_RIGHT: doMovement(RIGHT);
                        break;
                    case KeyEvent.VK_DOWN: doMovement(DOWN);
                        break;
                    case KeyEvent.VK_UP: doMovement(UP);
                        break;
                    default: System.out.println("oops1");
                        break;
                }
            }
        });
    }
 
    /**
     * will paint over frame including any components
     */
    public void paint(Graphics g) {
        Insets insets = getInsets();
        g.setColor(getBackground());
        g.fillRect(insets.left, insets.top, insets.left + 65, 25);
        //g.setColor(Color.blue);
        //g.drawRect(insets.left, insets.top, insets.left + 65, 25);
        int actualHeight = getHeight() - insets.top - insets.bottom;
        int x = (getWidth() - image.getWidth(this))/2;
        int y = insets.top + (actualHeight - image.getHeight(this))/2;
        g.drawImage(image, x, y, this);
        x = insets.left + 5;
        y = insets.top + 15;
        g.setColor(Color.red);
        g.drawString(s, x, y);
    }
 
    public void update(Graphics g) {
        paint(g);
    }
 
    public void run() {
        while (animate) {
            frames++;
            s = "frame "+frames;
            repaint();
            try {
                Thread.sleep(DELAY);
            }
            catch(InterruptedException ie) {
                System.err.println("run interrupt: " + ie.getMessage());
            }
        }
    }
 
    private void start() {
        frames = 0;
        animate = true;
        animator = new Thread(this);
        animator.start();
    }
 
    private void stop() {
        animate = false;
        animator = null;
    }
 
    private void loadImage() {
        Toolkit toolkit = Toolkit.getDefaultToolkit();
        image = toolkit.getImage("nebraska.jpg");
        MediaTracker mediaTracker = new MediaTracker(this);
        mediaTracker.addImage(image, 0);
        try {
            mediaTracker.waitForID(0);
        }
        catch (InterruptedException ie) {
            System.err.println(ie);
            System.exit(1);
        }
    }
 
    public static void main(String[] args) {
        new Viewer();
    }
}

[Dan Kottas]

Sorry I haven't got back to this in a while. I appreciate all of the great help on using windows! If anyone can figure out how to do this in a full screen window or knows why it's not working for me, please let me know. I'm really curious why this is.

Thanks,
-Dan