Creating an image from a panel

Question

Hi everybody,
I have a panel which extends JPanel, and wrote an image() method to extract the drawn image off the panel. For some reason, though, when I call this method, I get a dialog with a black box centered in it, and not the appropriate image.
My SSCCE is as follows:
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
public class MyPanel extends JPanel {
    private BufferedImage image;
    public BufferedImage image() {
        int x = getWidth();
        int y = getHeight();
        //image = new BufferedImage(x, y, BufferedImage.TYPE_INT_RGB);
        image = new BufferedImage(200, 200, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = image.createGraphics();
        SwingUtilities.paintComponent( g2, this, new JPanel(), 0, 0, x, y );
        g2.dispose();
        return image;
    public static void main( String args[] ) {
         MyPanel canvas = new MyPanel() {
              public void paintComponent( Graphics g ) {
                   Graphics2D g2 = (Graphics2D)g;
                   for( int i = 1; i <= 20; i++ ) {
                        int pos = i*50;
                        g2.drawString( "This is a test", pos, pos );
         JDialog test = new JDialog();
        JLabel label = new JLabel( new ImageIcon( canvas.image() ) );
        JScrollPane scroller = new JScrollPane( label );
        scroller.setPreferredSize( new Dimension( 500, 500 ) );
        test.add( scroller );
        test.pack();
        test.setVisible( true );
}I'm pretty sure it has something to do with the sizing of the image and the timing of the repainting--when I uncomment the commented line in image(), I get an error saying width and height can't be less than or equal to 0. But anyway, I need to paint and then show an image of what was painted, not the actual painted panel--that's what I'm having trouble with. If anyone could help me out, I'd appreciate it. Can anyone help me fix this, please?
Thanks,
Jezzica85
Edited by: jezzica85 on Jun 1, 2009 6:16 AM

Answer 1

Odd choice to both have the panel with a getImage() method, and also override paintComponent(Graphics).
Here is an alternate form of your code.
import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*;
public class MyPanel extends JPanel {
  private BufferedImage image;
  public BufferedImage image() {
    int x = 200;
    int y = 200;
    image = new BufferedImage(x,y, BufferedImage.TYPE_INT_RGB);
    Graphics2D g2 = image.createGraphics();
    g2.setColor(Color.yellow);
    g2.fillRect(0,0,x,y);
    g2.setColor(Color.black);
    for( int i = 1; i <= 20; i++ ) {
      int pos = i*50;
      g2.drawString( "This is a test", pos, pos );
    g2.dispose();
    return image;
  public static void main( String args[] ) {
    Runnable r = new Runnable() {
      public void run() {
        MyPanel canvas = new MyPanel();
        JDialog test = new JDialog();
        JLabel label = new JLabel( new ImageIcon( canvas.image() ) );
        JOptionPane.showMessageDialog(null, label);
        JScrollPane scroller = new JScrollPane( label );
        scroller.setPreferredSize( new Dimension( 500, 500 ) );
        JOptionPane.showMessageDialog(null, scroller);
    EventQueue.invokeLater(r);
}