How to draw PNG Image onto JPanel?

Question

I'm trying to draw a image onto a JPanel by overriding the paintComponent method. However, I'm having no luck with it at all and I don't know why.

Here's the code I've got at the moment:

DrawPanel

public class DrawPanel extends JPanel{

    private Image backgroundImg;

    public DrawPanel()
    {
        backgroundImg = Toolkit.getDefaultToolkit().createImage("C:\\Users\\Administrator\\workspace\\Scrub\\src\\loginBackground.png");
    }

    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.drawImage(backgroundImg, 0, 0, null);
    }
}

LoginWindow Class

import java.awt.*;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class LoginWindow extends Window{

    private DrawPanel panel;

    public LoginWindow(int width, int height)
    {
        super("", width, height);


        panel = new DrawPanel();
        this.add(panel);

        panel.setVisible(true);
    }
}

Main

public class Main
{
    public static void main(String[] args)
    {
        LoginWindow loginWindow = new LoginWindow(500, 300);


    }
}

you want background image right? then maybe this can help you http://stackoverflow.com/questions/22203049/java-background-not-showing-up/22203780#22203780 — Frakcool, Mar 05 '14 at 20:18

MadProgrammer · Answer 1 · 2014-03-05T20:48:00.993

There are lots of reasons this might not work

The image might not be getting loaded. You should use ImageIO.read instead, as it will throw an IOException if something goes wrong
The layout manager is using the preferred size of your panel, which is defaulted to 0x0, making the component effectively invisible
You're not setting the window to be visible...

For example

public class DrawPanel extends JPanel{
    //...
    public Dimension getPreferredSize() {
        return backgroundImg == null ? new Dimesion(100, 100) : new Dimension(backgroundImg.getWidth(this), backgroundImg.gtHeight(this));
    }

And then in your Window class...

public LoginWindow(int width, int height)
{
    super("", width, height);


    panel = new DrawPanel();
    this.add(panel);

    // Swing components are visible by default
    //panel.setVisible(true);
    // windows aren't
    setVisible(true);
}

A simpler soliton would be to use a JLabel...

setLayout(new BorderLayout());
BufferedImage img = ImageIO.read(new File(...));
JLabel label = new JLabel(new ImageIcon(img));
add(label);
setVisible(true);

Take a look at How to use Labels and Reading/Loading an Image for more details

Sorry for the confusion. About what you've said for Window's being visible. The LoginWindow extends to another class called Window that I have created. In this super class, I have `setVisible(true)` so it doesn't needs to be called again. In fact, the window shows it's just not drawing the image, thats all. — Danny, Mar 05 '14 at 21:27
Okay, lesson, try and avoid using class names that already exist if you can or identify them early on. The rest should be valid... — MadProgrammer, Mar 05 '14 at 22:31

How to draw PNG Image onto JPanel?

1 Answers1