JPanel size

[Juhan Voolaid]

Hi
I don't understand why i don't get my screen size (it gives me 0) with the same way that it get it in my paint method. In paintComponent i have a function fillRect(0, 0, getWidth(), getHeight(), this); nad it works and fills my screen with given colour. But in same class, in constructor i want to give values to int x, y; , so that x=getWidth()/2 and y=getHeight()/2 -- but it gives 0. What's the problem? How should i assign those values to x and y?
code:

  
private class gamePanel extends JPanel implements ActionListener, Runnable{

Image hero_back=Toolkit.getDefaultToolkit().getImage("hero.gif");

int x, y; 
int delay=200; //0.2 sek


public gamePanel(){
x=super.getWidth()/2; //0
y=getHeight()/2;//0
System.out.println("width: " +this.getWidth());//still 0
repaint();
}

public void paintComponent(Graphics g){

Graphics2D g2D=(Graphics2D)g;
g2D.setColor(Color.black);

g2D.fillRect(0, 0, getWidth(), getHeight());//but works here

g2D.drawImage(hero_back, x, y, this);

}

public void run(){



}

public void actionPerformed(ActionEvent e){


}

}

[ February 28, 2004: Message edited by: Juhan Voolaid ]

[Don Kiddick]

a) getWidth() & getHeight() will return the size of your gamePanel, not the size of your screen.
b) the first call to getWidth() & getHeight() occurs in your constructor. At this time the height & width is zero. Later on (presumbly after you've added the gamePanel to another container) paintComponent() gets called and by that time your gamePanel's height & width is not zero.
D.

[Juhan Voolaid]

yes i ment the size of the panel not the whole screen - thnx, but what should i do to know where the center is after i have created the gamePanel object?
[ February 28, 2004: Message edited by: Juhan Voolaid ]

[Don Kiddick]

Just calculate it when you need it :

 
private Dimension getCentre() {
  return new Dimension( getWidth(), getHeight() );
}

D.

[Juhan Voolaid]

OK i still have difficulties to solve this problem.
U told to use this method getCenter() by creating new Dimension, but it still gives 0.
I want to use it only when i have created the object - then i suppose in constructor.
Could u please do this code so that. When i have created the gamePanel class - i have 2 int-s x and y that are the center cordinates of this panel.

 
private class gamePanel extends JPanel{
 int x, y;
 public gamePanel(){
  //code here so that x=getWidth()/2 and y=getHeight()/2
 }
}

I'm sure it is one simple thing that i don't understand clearly. Please help.

[Don Kiddick]

don't put the code in the constructor. When the panel is constructed it does not have a width or a height as it's not displayed anywhere.
My advice was to calculate the centre of the screen whenever you need to use it.
Does that make sense ? If not show me the code where you use the centre of the screen and I'll show you what I mean.
D.

[Juhan Voolaid]

OK i see now. But what i want to do is - is so that if my program starts - there is a image at the center position. So my class code is similar to what i gave u as a sample. Only it has loaded a image and has paintComponent() method. But in the paintComponent is drawImage() and it takes arguments int x and y as cordinates. So thats why i want to create x, y dynamically.
ok here is code:

  
private class gamePanel extends JPanel {

Image hero_back=Toolkit.getDefaultToolkit().getImage("hero.gif");

int x;
int y; 


public gamePanel(){

}

public void paintComponent(Graphics g){

Graphics2D g2D=(Graphics2D)g;
g2D.setColor(Color.black);

g2D.fillRect(0, 0, getWidth(), getHeight());

g2D.drawImage(hero_back, x, y, this);

}


}

[Don Kiddick]

Why can't you just do this ?

 
private class gamePanel extends JPanel {
        Image hero_back=Toolkit.getDefaultToolkit().getImage("hero.gif");
        public gamePanel(){}
        public void paintComponent(Graphics g){
                Graphics2D g2D=(Graphics2D)g;
                g2D.setColor(Color.black);
                g2D.fillRect(0, 0, getWidth(), getHeight());
                g2D.drawImage(hero_back, getWidth() / 2, getHeight() / 2, this);
         }
}

D.
[ March 02, 2004: Message edited by: Don Kiddick ]

[Juhan Voolaid]

because i will use drawImage() later when i animate the image by calling repaint(). Thats's why i want x and y to have values.
[ March 02, 2004: Message edited by: Juhan Voolaid ]

[Don Kiddick]

so, everytime you use drawImage, just do this :

 
g2D.drawImage(hero_back, getWidth() / 2, getHeight() / 2, this);
 

I don't see the problem.
D.

[Don Kiddick]

From your other post, I've realised what you want to do now. Try lazily instantiating the position, like this :

 
import java.awt.Point;
private class gamePanel extends JPanel {
    Image hero_back = Toolkit.getDefaultToolkit(  ).getImage( "hero.gif" );
    
    private Point heroPosition;
    public gamePanel(  ) {}
    
    private Point getHeroPosition() {
        if( this.heroPosition == null ) {
            this.heroPosition = new Point( getWidth() / 2, getHeight() / 2);
        }
        return this.heroPosition;
    }
    public void paintComponent( Graphics g ) {
        Graphics2D g2D = (Graphics2D) g;
        g2D.setColor( Color.black );
        g2D.fillRect( 0, 0, getWidth(  ), getHeight(  ) );
        g2D.drawImage( hero_back, getHeroPosition().x, getHeroPosition().y, this );
    }
}

Always use getHeroPosition() rather than accessing the instance variable directly.
does that help ?
D.