Re: how to clear the image from jpanel

From:
Knute Johnson <nospam@rabbitbrush.frazmtn.com>
Newsgroups:
comp.lang.java.programmer
Date:
Thu, 28 Oct 2010 14:45:21 -0700
Message-ID:
<U9myo.1977$d67.455@newsfe16.iad>
On 10/28/2010 11:50 AM, John B. Matthews wrote:

In article<ddhyo.3138$lM.1269@newsfe23.iad>,
  Knute Johnson<nospam@rabbitbrush.frazmtn.com> wrote:

On 10/28/2010 6:30 AM, jimgardener wrote:

I have an ImagePanel subclassed from JPanel ,where I can set an image

class ImagePanel extends JPanel{
    private BufferedImage bi;
    public ImagePanel(){
        super();
    }
    public void setImage(String imagefilename) throws IOException{
        bi = ImageIO.read(new File(imagefilename));
        this.setPreferredSize(new Dimension(bi.getWidth(),bi.getHeight()));

        this.revalidate();
        this.repaint();
          }
         @Override
    public void paintComponent(Graphics g) {
          g.setColor(getBackground());
          g.fillRect(0,0,getWidth(),getHeight());
          g.drawImage(bi,0,0,null);
          }
}

I can set the image by giving an image filename.But I wish to clear
the previous image from the panel,thus showing a blank image
panel,if a user supplies an invalid image name. How can I do
this?Can someone please tell me?

[...]

If no image gets loaded, set the reference to null and test for that
in the paintComponent() method and don't draw the image just clear
the background.


Knute's right; and if you forget the test, as I have sometimes done, the
drawImage() method "does nothing if img is null."

<http://download.oracle.com/javase/6/docs/api/java/awt/Graphics.html>


I never noticed that before. I must have been trying to protect against
a NullPointerException that never gets thrown.

--

Knute Johnson
email s/nospam/knute2010/

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