JScrollPane child dimesniosn not updating

[rareseu]

Hy guys ! i'm running into a bit of trouble with a JScrollPane, the pane itself has to stay the same size but the viewport inside the pane has to get longer as i add stuff to it( right now i'm just drawing circles downwards) the problem is that when the viewport gets big enough to require scrolling my drawing dissapears my globals :

//global variables :
//params for the circle i draw :
public int positionY=10;
public int positionX=20;
public int width=30;
public int height=30;

//used to set dimension of the viewport :
private Dimension dim=new Dimension();

//the viewport in which i draw, it extends JViewport
private MyJViewport drawHere=new MyJViewport();

private JScrollPane displayResult;

private JButton jButton1;

the MyJViewport class :

class MyJViewport extends JViewport {

    @Override
    public void paint(Graphics g) {
        g.setColor(Color.BLUE);
        g.fillOval(positionX, positionY, width, height);

    }//paint
    
}//MyJViewport

in the constructor i instance the scrollpane :

displayResult = new javax.swing.JScrollPane(drawHere);
displayResult.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
displayResult.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

the event handler for the button press:

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
//the new circle will be positioned under the previous
positionY+=height;

    // if the point where the circle gets drawn exceeds the bounds of the viewport
    // resize the viewport
    if (positionY > drawHere.getHeight()) {
            dim.height = drawHere.getHeight() + height;
            dim.width = drawHere.getWidth();
            drawHere.setPreferredSize(dim);
            drawHere.revalidate();
            
        }//if

    drawHere.repaint();
}

can anyone help with this ?

[Nagy Vilmos]

It looks like you are only painting the last item.

---

Panic, Chaos, Destruction. My work here is done.

[rareseu]

I don't understand :| , do you mean the last item in the scrollpane ? there is only the viewport in there, can you please explain ?

[Nagy Vilmos]

All your code is doing is painting a circle at the LAST position. The repaint needs to paint EVERY circle. The simplest approach is to have a collection of objects each representing on of the thing you wish to display. Each class knows how and where to piant itself on a given graphic: [this code is not tested]

// you need a 'circle' class
class MyCircle
{
private int top;
private int left;
private int radius; // don't need two vars here

MyCircle (int top, int left, int radius)
{
this.top = top;
this.left = left;
this.radius = radius;
}

void Repaint (Graphic g)
{
g.setColor(Color.BLUE);
g.fillOval(this.top,
this.left,
this.radius,
this.radius);
}
}

As you add your curcles create a new object with the X,Y,R. Hold these in a list object. On the scrollpane repant iterate through the list and paint each object.

---

Panic, Chaos, Destruction. My work here is done.

[rareseu]

I see now :) thank you for explaining !