如何从其JPanel内容更改JDialog图标？

Question

I've a JDialog and JPanel

---

...
MyPanel panel = new MyPanel();
JDialog dialog = new JDialog();
dialog.add(panel);
dialog.show();
...

---

public class MyPanel extends javax.swing.JPanel {
    ....
}

How can I change the icon of dialog from MyPanel class when it is opened?

My code:

...    
initComponents();

1. ((JFrame)((JDialog)this.getParent()).getOwner()).setIconImage(img);

2. Window win = SwingUtilities.getWindowAncestor(this);
   win.setIcon(img);

Both are returning NullPointerException

Answer 1

It returns null because you're calling these methods from withing the constructor of the panel. And when the panel is constructed, it's not added to the dialog yet.

Either set the icon from the outside:

MyPanel panel = new MyPanel();
JDialog dialog = new JDialog();
dialog.add(panel);
dialog.setIconImage(...);
dialog.show();

or add an AncestorListener to the panel to be notigied when it's being made visible, and set the icon from the listener method.