Refreshing picture in drawingPanel extends JPanel

Question

I have to load a small icon on the botton of my software. just to have a loading/ok/error icon. as sudgested on "http://www.particle.kth.se/~lindsey/JavaCourse/Book/Part1/Java/Chapter06/images.html" i create a dwowing panel extending JPanel.

class drawingPanel extends JPanel
{
    Image img;

    drawingPanel (Image img){
        this.img = img;
    }

    public void paintComponent (Graphics g) {
        super.paintComponent (g);

        // Use the image width & height to find the starting point
        int imgX = getSize ().width/2 - img.getWidth (this);
        int imgY = getSize ().height/2 - img.getHeight (this);

        //Draw image centered in the middle of the panel    
        g.drawImage (img, imgX, imgY, this);
    } // paintComponent

}

I initialize the component in the following way:

// Grab the image.
Image img = new ImageIcon(iconPath+"ok.png").getImage();
// Create an instance of DrawingPanel
iconPanel = new drawingPanel(img);

all works well but at runtime i want to be able to change the icon within the pannel. i tryed all the fo;llowing but none managed to view the new picture:

Image img = new ImageIcon(iconPath+"loading.gif").getImage();
// Create a new  instance of DrawingPanel
this.iconPanel = new drawingPanel(img);
this.iconPanel.repaint();
this.iconPanel.revalidate();
this.iconPanel.repaint();
this.repaint();
this.revalidate();

(i tryed this because the class in whic i am writing the code is another extension of JPanel that contains IconPanel. Any idea about why i do not manage to change the picture?

Thanks, Stefano

Answer 1

First thing don't start class name with small name. Rename drawingPanel to DrawingPanel.

I have tried making a simple demo based on your description and it works fine. The image in panel is changing perfectly.

public class Demo {

    public Demo() {
        JFrame frame = new JFrame();
        frame.setSize(400, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());

        // Grab the image.
        Image img = new ImageIcon("1.png").getImage();
        // Create an instance of DrawingPanel
        final DrawingPanel iconPanel = new DrawingPanel(img);

        frame.add(iconPanel, BorderLayout.CENTER);

        JButton button = new JButton("Change image..");
        frame.add(button, BorderLayout.NORTH);

        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                iconPanel.setImg(new ImageIcon("2.png").getImage());
                iconPanel.repaint();
            }
        });

        frame.setVisible(true);
    }

    public static void main(String[] args){
        new Demo();
    }
}

class DrawingPanel extends JPanel {
    Image img;

    DrawingPanel(Image img) {
        this.img = img;
    }

    public void setImg(Image img) {
        this.img = img;
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        // Use the image width & height to find the starting point
        int imgX = getSize().width / 2 - img.getWidth(this);
        int imgY = getSize().height / 2 - img.getHeight(this);

        // Draw image centered in the middle of the panel
        g.drawImage(img, imgX, imgY, this);
    } // paintComponent

}

The changes I have made is add a setter method of img in DrawingPanel class. So instead of creating new DrawingPanel you just have to call setImg() with new Image and then call reapint to paint the new image.