java - Width and height of a JPanel are 0 (Specific Situation)

Question

Please pardon me if this is hard to follow, but I have a specific problem that I need help solving. I have done a ton of research, and I have tried numerous solutions but none of them are working.

My issue is that I have an ImagePanel class that is extending JPanel (code below), this class needs to use width and height to scale images (I am making a program where users can create custom tutorials including images). When I instantiate this I get an error saying that the width and height must be nonzero. I understand that this is because the layout manager has not yet passed the ImagePanel a preferred size, however I do not know how to get that size to the panel. The ImagePanel is inside a JPanel which is inside a JSplitPane inside of a JScrollPane inside of a JPanel inside of a JTabbedPane inside of a JSplitPane inside of a JFrame. A graphical representation of this in decreasing container order is as follows:

1. JFrame (GridLayout)
2. JSplitPane (Default SplitPane Layout)
3. JTabbedPane (Deault JTabbedPane Layout)
4. JPanel (GridLayout)
5. JScrollPane (Default ScrollPane Layout)
6. JSplitPane (Default SplitPane Layout)
7. JPanel (GridLayout);
8. ImagePanel

The code for the ImagePanel is as follows:

import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JPanel;

public class ImagePanel extends JPanel{

    private BufferedImage i;
    private ImageIcon miniature;
    private Image paint = null;

    public void createImage(String path){
        try {                
            i = ImageIO.read(new File(path));
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        if(i != null){
            int width = (int)((double)i.getWidth() * ((double)getWidth()/i.getWidth()));
            int height = (int)((double)i.getHeight()*i.getHeight()/i.getWidth()*((double)this.getHeight()/i.getHeight()));
            miniature = new ImageIcon(i.getScaledInstance(width, height, Image.SCALE_SMOOTH));
            paint = miniature.getImage();
        }

    }


    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (paint!=null){
            g.drawImage(paint, 0, 0, null);}     
    }

}

How can I get the proper size to the ImagePanel. I would like the image to change size with the size of the JFrame, which is why I don't just use setPreferedSize();.

Answer 1

I would like the image to change size with the size of the JFrame

Instead of doing custom painting in your own component you can use Darryl's Stretch Icon. The Icon will automatically be resized based on the space available.

which is why I dont just use 'setPreferedSize();'.

If you do use custom painting then you should NOT use setPreferredSize(). You SHOULD be overriding the getPreferredSize() method to return the size of the image. Remember the preferred size is just a suggestion to the layout manager. The layout manager can use or ignore the size.

If you want to scale the image automatically in your paintComponent() method then the code should be:

Dimension d = getSize();
g.drawImage(paint, 0, 0, d.width, d.height, this);

So the real challenge in your code (no matter which solution you choose) is to make sure you are using a layout manger that will give all available space to your component so the image can be scaled automatically.