Re: JPanel used for graphics

Frank, 

Here's a clarification. 

I had proposed a simple way to use subclassed components by allowing the 
user to intitialize them.  My original text was 

> The Swix engine could check 
> to see if a variable to which a tag is bound already has a non-null value.  
> If it's null, then it should create a new instance as it does now.  If it's 
> non-null and it's an instance of the appropriate type, then the xml 
> attributes should be applied to the existing value.  I'm not sure whether 
> it's an easy solution to any other problems, but it would be a simple 
> solution to my subclassing problem.

Here are some snippets of code to illustrate what I mean more concretely. 

=== From XML file =======================
<!-- I want a panel (xc_panel) in the frame, but really want it to be a
    Diagram (subclass of JPanel).  See below. -->
. . .
<panel id="xc_panel" preferredSize="500,500" 
constraints="BorderLayout.CENTER">
</panel>
. . . 

=== From Diagram.java =============================
// This is the subclass of JPanel that I want xc_panel to be.
public class Diagram extends JPanel {
. . .
   public paintComponent(Graphics g) {
      // Draw my diagram to repaint the panel.
      . . .
   }
} 

=== From my main class ===========================
// A possible solution is the following.  Note that THIS DOES NOT WORK
// because Swixml always creates a new JPanel from the xml file
// and overwrites my assignment to xc_panel.
public class MyController {
   . . .
   public Diagram xc_panel;   // This is initialized by swixml
   . . .
   public MyController() {
       xc_panel = new Diagram();   // I WOULD LIKE THIS TO WORK.
       SwingEngine swix = new SwingEngine( this );
       swix.render( "XXX.xml" );
       . . . // render() has assigned a new panel to xc_panel :-(
   }
. . . 

The Diagram/JPanel variable xc_panel is specified in the .xml and
initialized by the swix.render call.  What I'd prefer the SwingEngine
to do it take a look at the contents of xc_panel before it creates
a new JPanel.  If xc_panel already contains a JPanel, as my example
does, it should not create a new one, but use the existing one and
simply apply any specifed attributes to it -- in my case a preferred
size of 500x500 was specified. 

This appears to be a simple solution to my problem where I must subclass
JPanel to override paintComponent().  I believe allowing user initialization
of components might also provide a solution to problems that initclass can't
easily solve. 

 -- Fred 

 

 

 

[email protected] writes: 

> List for Users of Carlsbad Cubes' Technologies and Products schrieb am 27.03.04 18:16:58:
>> 
>> It appears that the way to do this is to register a new tag for this 
>> subclass of JPanel that I've defined.  Is this the correct approach? 
> 
> At least this seems the most reasonable thing to me.
> Easy, documented and IMHO well used. 
> 
>> 
>> This got me to thinking about other approaches.  The Swix engine could check 
>> to see if a variable to which a tag is bound already has a non-null value.  
>> If it's null, then it should create a new instance as it does now.  If it's 
>> non-null and it's an instance of the appropriate type, then the xml 
>> attributes should be applied to the existing value.  I'm not sure whether 
>> it's an easy solution to any other problems, but it would be a simple 
>> solution to my subclassing problem. 
> 
> Could you please explain this with some (pseudo) code? I do not
> grab it... 
> 
> Frank 
> 
>  
> 
> 
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