how to clear the image from jpanel

[jimgardener]

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?
thanks

jim

[Knute Johnson]

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 Johnson
email s/nospam/knute2010/

[John B. Matthews]

In article <ddhyo.3138$lM....@newsfe23.iad>,
Knute Johnson <nos...@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>

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>

[Knute Johnson]

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