Adding scrollbars to a panel containing a buffered image

Question

Frame Class:
package HeatMap;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridBagLayout;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ScrollPaneConstants;
import javax.swing.SwingUtilities;
class HeatMapFrame extends JFrame
     BufferedImage img;
     HeatMapFrame(BufferedImage img)
          super("Gene Expression Profile Heatmap");
          this.img = img;
          HeatMapPane mapPanel = new HeatMapPane(img);
          JScrollPane scrollPane = new JScrollPane(mapPanel, ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS,   
                                          ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS );   
          scrollPane.setPreferredSize(new Dimension(640,480));
          add(scrollPane,BorderLayout.CENTER);
          setSize(640,480);
          setLocation(getWidth()/4,getHeight()/4);
          setDefaultCloseOperation(EXIT_ON_CLOSE);
          setVisible(true);
Panel Class:
package HeatMap;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.AffineTransform;
import java.awt.image.BufferedImage;
import javax.swing.JPanel;
public class HeatMapPane extends JPanel
     BufferedImage img;
     HeatMapPane(BufferedImage img)
          this.img = img;
          //setSize(640,480);
     protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // Draw image centered.
        //int x = (getWidth() - img.getWidth())/2;
        //int y = (getHeight() - img.getHeight())/2;
        g.drawImage(img, 0, 0, this);
}I`m drawing the BufferedImage to a JPanel and addig the JPanel to a JScrollPane. The problem is that the scrollbars are visible but not active. Scrolling is not working. Can somebody tell me why? Thanks for any advice.

Answer 1

Since your HeatMapPane does not declare a preferred size, I'm guessing(1) it is assigned a size of 0x0.
1) I would do more than guess, if you had posted an SSCCE. For an SSCCE to do with images, you might hot-link to some of the images available at my [media page|http://pscode.org/media/#image], or generate an image within the source.