JScrollPane function with Custom Paint ???

Question

Hi, I'm having a problem with scrolling with components for which I've overidden the paint method for.
I have a scrollpane which contains a ContentPanel (my own subclass of JPanel in which I implemented paint and paintComponent). The ContentPanel contains Subclasses JButton's which also have their own paintComponent methods.
Problem: Everything (including scrollbars) paint correctly initially. The problem arises when one tries to scroll. When I pull the scrollbar in any direction, the JButtons paint oscillate between painting themselves at the correct scrolled position and at the original position in the Viewport. Then when one lets go of the scroll, the component rests in exactly the same position in the Viewport as it started.
I tried implementing the Scrollable inteface, still no luck. The documentation seems to imply that custom painting should have no effect on scrolling because the content is contained in the view and the ScrollBar commissions a Viewport class to help it move around. I'm not sure, but it seems like it should not be the result of my overidding the paint methods.
I'm so confused, is there something else I need to implement to use JScrollPanes, like Adjustment Listener?
Thanks for your help, Aurora

Answer 1

Dear Tom,
It looks like the code you have was originally made for awt, not swing. In swing, one should override the paintComponent(Graphics g) method, not the paint() method.
For reasons why check out this tutotial on how painting works.
http://java.sun.com/docs/books/tutorial/uiswing/overview/draw.html
The reason why you need to call super.paintComponent() in the JPanel is because the JPanel you have is not completely opaque, (I think). Anyway, it has to do with how painting works.
public class myPanel extends JPanel
public myPanel()
setVisible(true);
setSize(600,200);
setLayout(null);
setBackground(Color.white);
myBox m1 = new myBox();
//is the bounds of myBox set appropriately??? Perhaps you need to setBounds() in the constructor of mybox.
add(m1);
public void paintComponent(Graphics g)
super.paintComponent(g);
g.setColor(Color.black);
g.drawString("Test", 10, 13);
m1.paint(g);
//this is important. The subcomponents will not paint themselves unless they are told to by their containers.
In Swing, basically painting works as a hierarchy where the top level Component paints itself and then paints all it's children component, they paint their children and so on. Swing also determines many important things using the bounds of each component. To ensure correct painting and listening behavior, make sure the bounds for your myBoxes are the correct size. Also, implement public void paintComponent(Graphics g) in the myBox so that it will draw it's own rectangle when called by myPanel.
If that doesn't work, check out how myPanel is being added to the overall JFrame. It may not be displaying correctly because you have forgotten to add it or don't have a layout manager etc.
Good luck,
Aurora