JPanel doesn't update until resize Jframe

Question

I subclass JPanel to overwrite paintComponent(Graphics), I want to draw an image onto jpanel in a jframe.

But my image hasn't shown up until I make a change to jframe's size. This is my code:

public class ImagePanel extends JPanel{

    public void setImage(BufferedImage bi)
    {
        image = bi;
        revalidate();
    }

    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        if(image != null)
        {
            g.drawImage(image, 0, 0, this);
        }
    }
}

Answer 1

Verify that you invoke setVisible() after adding components and calling pack(), as discussed in this related example. You may also need to adopt an appropriate layout. Invoking repaint(), as suggested here, may fix the symptom but not the underlying cause.

Answer 2

If you want to "refresh" the JPanel then you should call repaint(), which will call your paintComponent(). This should fix your problem:

public void setImage(BufferedImage bi)
{
    image = bi;
    EventQueue.invokeLater(new Runnable()
    {
        public void run()
        {
            repaint();
        }
    });
}

Its good practice to update and change the GUI using the EDT. Heres more info on the EDT if you're interested:

How does the event dispatch thread work?

repaint doesn't need to be called from the EDT. If you're changing the GUI, such as setting text to a JLabel, it should be inside of the EDT. Heres more information on what can be called outside of the EDT (courtesy of nIcE cOw):

Safe to use Component.repaint() outside EDT?