CODEWITHSUNDEEP
javaimageswingappletjframe
Parker
Parker

Reputation: 8851

Can't get JFrame to refresh image

Hey, so I'm working on a program and for debugging purposes, I'm trying to get the program to take a screenshot of a part of the display. I want to have the display updated, but I can't seem to get it to work. I'm sure it's a simple issue, but my experience with Java Applets is very small.

Here's the part that I'm having issues with:

...
Thread.sleep(5000);
    try {gb = new GameBoard(frame.getBounds());}
    catch(Exception e){System.out.println("Error.");} // Make "gameboard" Object

    while (true)
    {
        Thread.sleep(1000);
        gb.grabImage(); // use java.awt.Robot's createScreenCapture()

        ImageIcon icon = new ImageIcon(gb.image()); // wrap the image 
        JLabel label = new JLabel(icon, JLabel.CENTER);
        frame.getContentPane().add(label,BorderLayout.EAST); //display the image (works)
        //JOptionPane.showMessageDialog(null, label, "icon", -1);
        label.repaint(); //update the display??
        frame.repaint();
        frame.getContentPane().repaint();
    }

As I said, the image appears, and will create new ones if I change the Applet size, but I need a constantly changing image.

Thanks in advance!

Upvotes: 2

Views: 7109

Answers (3)

Cameron Skinner
Cameron Skinner

Reputation: 54516

You are creating and adding a new JLabel each time through the loop. Because you are changing the structure of the component tree you'll need to call revalidate on the frame's content pane.

A better solution would be to just change the image on a single JLabel. Create one label, add it, then in your loop use JLabel.setIcon and repaint.

Upvotes: 5

user541686
user541686

Reputation: 210765

From what I remember, repaint() in Java should really have been called invalidate() -- it doesn't actually repaint the window; it only invalidates it so it can be repainted by the OS at the next opportunity. I didn't look carefully at your code, but I think this might be the issue. I'm not sure how to force a redraw, but an idea would be to return from the function, then have a timer interrupt you and paint it then -- that way, the OS will have a chance to paint the window.

Upvotes: 0

trashgod
trashgod

Reputation: 205875

As @RD notes, createScreenCapture() will throw a SecurityException if the applet is not signed. Sleeping on the event dispatch thread may be blocking updates. This example captures a screen image as the mouse is dragged; its BufferedImage "remembers" the last image captured.

Upvotes: 2

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