🚀 go-pugleaf

Qiang Song wrote:
> 
> I solved this problem by overriding the getPreferredSize function.
> 
>  public Dimension getPreferredSize(){
>     return new Dimension(img.getWidth(null), img.getHeight(null));
>   }
> 
> This can not be solved by setting the canvas size!

The reason you have to override this method is that
Canvas.getPreferredSize() really has no way of knowing
that the "img" instance variable of your subclass "myCanvas"
even exists.  

Wihelmsen's suggestion that you base your subclass on
JComponent would obviate the need to override 
"getPreferredSize()" if you invoke "this.setPreferredSize()"
immediately after loading your image in the constructor
of your subclass.

 public myJCanvas(){
  //you may change image to your own
  img = Toolkit.getDefaultToolkit().getImage("AboutSwing.gif");

  // add this ...
  this.setPreferredSize(new Dimension(img.getWidth(null), img.getHeight(null)));
 }


In addition, you may want to make sure that any 
view/component you place into the JViewport 
implements the Scrollable interface.  This will
give your object control over the scrolling units.


Paul Furbacher