CODEWITHSUNDEEP
javaswing
Gerry
Gerry

Reputation: 79

JPanel and PaintComponent

I am really having problems understanding how overriding the paintComponent(Graphics g) method works.

I have the following class:

public class DisplayDocs2 extends JPanel {
    ArrayList <BufferedImage> docList;
    BufferedImage imageCount;

    public DisplayDocs2(ArrayList docList){
        this.docList = docList;
    }

    public JPanel DisplayImage(){
        this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));

        for (int i = 0; i < docList.size(); i++){
            imageCount = docList.get(i);
        }
        return this;
    }

    @Override
    protected void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(imageCount, 0, 0, this);
    }
}

Whatever I try, if I have more than one image then the first image is always covered by the last one.

I want to use BufferedImages because I want to be able to manipulate them afterwards.

Upvotes: 0

Views: 153

Answers (4)

Gilbert Le Blanc
Gilbert Le Blanc

Reputation: 51565

I am really having problems understanding how overriding the paintComponent(Graphics g) method works.

It's pretty simple. Every time the system or you call for a repaint of the JPanel, the code in the paintComponent method is executed.

In the paintComponent method, you paint. Period. Full stop. You do nothing else in the paintComponent method but paint (draw).

The first thing you do is create a Java object that holds a BufferedImage and a java.awt.Point to hold the x, y position of the BufferedImage.

package com.ggl.testing;

import java.awt.Point;
import java.awt.image.BufferedImage;

public class ImageLocation {

    private final BufferedImage image;

    private Point imageLocation;

    public ImageLocation(BufferedImage image, Point imageLocation) {
        this.image = image;
        this.imageLocation = imageLocation;
    }

    public Point getImageLocation() {
        return imageLocation;
    }

    public void setImageLocation(Point imageLocation) {
        this.imageLocation = imageLocation;
    }

    public BufferedImage getImage() {
        return image;
    }

}

Next, you pass a List of ImageLocation instances to your drawing panel.

Finally, your paintComponent method would look something like this:

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

        for (ImageLocation imageLocation : imageLocations) {
            Point p = imageLocation.getImageLocation();
            g.drawImage(imageLocation.getImage(), p.x, p.y, this);
        }
    }

You create the List of ImageLocation instances somewhere else in your code. Preferably in a GUI model class.

Upvotes: 3

mpocsaji
mpocsaji

Reputation: 126

The behaviour you experiencing is the result of your code. The part:

        for (int i = 0; i < docList.size(); i++) {
            imageCount = docList.get(i);
        }

Sets the imageCount reference to the last element of the list, which the paintComponent() method draws. So your first image is not covered, it is not painted at all.

If you want to draw all the images,

  1. Remove the for cycle above and the imageCount attribute, they are unnecessary.

  2. Put a code like this into your paintComponent():

    super.paintComponent(g);
int x = 0;
for (BufferedImage img : docList) {
    g.drawImage(img, x, 0, this);
    x += img.getWidth();
}

This will paint all your images next to each other. (Note that the code will throw NullPointerException if the method DisplayDocs2 is never called with a non-null parameter.

Upvotes: 2

SomeDude
SomeDude

Reputation: 14238

You can actually use jlabel instead of paintComponent.

for (int i = 0; i < docList.size(); i++)
{
    imageCount = docList.get(i);
    JLabel label = new JLabel( new ImageIcon( imageCount ) );
    this.add ( label );
}

Upvotes: 0

jmj
jmj

Reputation: 649

Because of this :

 g.drawImage(imageCount, 0, 0, this);

Try to do something as :

g.drawImage(imageCount, x, y, this); // x, y should have dynamic values.

Hope this Helps.

Upvotes: 0

Related Questions