直接绘制到面板中的JButton不能通过WindowsLookAndFeel显示背景

Question

So, I'm developing a drag-and-drop style visual designer in Java using Swing.

Since the components that you see on the designer aren't actual components, only a visual representation (eg buttons can't be clicked, text fields can't accept text, etc) I'm painting them directly on my panel, overriding the methods getX() , getY() , getWidth() and getHeight() .

It works perfectly fine on any LookAndFeel except for WindowsLookAndFeel. There, for some reason, the backgrounds of JButtons are not being painted. I have to use Windows LookAndFeel for the designer because that's how our software is deployed, and if I use a different LookAndFeel the designer layout will not be the same as our software.

I've lost a few hours trying to solve this problem, and I suspect that it's happening because by not adding the JButton on a container, it's native peer has not been instantiated. I've tried to create the peer manually, but without success.

I have noticed this problem on Windows 7 (With Aero) and Windows 8. If I use the classic theme on Windows 7 it works, so I assume it also works on Windows XP (But I haven't tested this). I'm using Java 1.7.0_25-b17 to test this.

Here's a sample I've made to show the problem:

package test;


import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestSwing {

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) { }

        JFrame f = new JFrame();
        f.setSize(300, 150);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        f.getContentPane().setLayout(new BoxLayout(f.getContentPane(), BoxLayout.X_AXIS));
        JPanel p1 = new JPanel();
        p1.setPreferredSize(new Dimension(150, 150));
        p1.setBorder(BorderFactory.createLineBorder(Color.yellow));
        p1.add(new JButton("Test"));
        f.add(p1);

        final MyButton b = new MyButton();
        b.addNotify();

        JPanel p2 = new JPanel() {
            @Override   
            public void paint(Graphics g) {
                super.paint(g);
                b.paint(g);
            }
        };
        p2.setPreferredSize(new Dimension(150, 150));
        p2.setBorder(BorderFactory.createLineBorder(Color.red));

        f.add(p2);
        f.setVisible(true);
    }

    private static class MyButton extends JButton {
        public MyButton() {
            super("Test");
        }

        @Override
        public int getWidth() {
            return 70;
        }
        @Override
        public int getHeight() {
            return 25;
        }

    }
}

---

Here's the sample using WindowsLookAndFeel:

And here with MetalLookAndFeel:

Answer 1

As a potential solution. You could use a class like Screen Image to create an image of the button. Then just display the image an an Icon on a JLabel an you will have a real component to work with that you can drag around.

Answer 2

Ok, I found it, thanks to your sugestion @camickr.

All I had to do was call setSize(int width, int height) before painting it. Looking at the Component source code, I've found this on the resize method (Called by setSize ):

setBoundsOp(ComponentPeer.SET_SIZE);

I assume that this command tells the native component that it's size has changed, and without calling it the background is actually being painted, but with size 0x0.

So now, instead of creating a class MyButton and overriding the getWidth() and getHeight() methods, all I have to do is the following:

final JButton b = new JButton("Test");
b.setSize(70, 25);

And still paint it on my JPanel.