通过实现PanelUI在JPanel上绘图：
import java.awt.Image;
import java.awt.MediaTracker;
import java.awt.Toolkit;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class ImgPanel extends JPanel
{
private Image img;
public ImgPanel()
{
}
public void updateUI()
{
setUI(ImgPanelUI.getInstance());
}
public Image getImg()
{
return img;
}
public void setImg(Image image)
{
img = image;
}
public static void main(String[] args)
{
try
{
JFrame frame = new JFrame("test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Image img = Toolkit.getDefaultToolkit().getImage(ImgPanel.class.getResource("test.jpg"));
ImgPanel panel = new ImgPanel();
MediaTracker tracker = new MediaTracker(panel);
tracker.addImage(img, 1);
tracker.waitForID(1);
System.out.println("load image ok");
panel.setImg(img);
panel.add(new JButton("test1"));
panel.add(new JButton("test2"));
frame.getContentPane().add(panel);
frame.setSize(640, 480);
frame.setLocation(80, 60);
frame.setVisible(true);
}
catch(Throwable e)
{
e.printStackTrace();
System.exit(1);
}
}
}
import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.plaf.ComponentUI;
import javax.swing.plaf.basic.BasicPanelUI;
public class ImgPanelUI extends BasicPanelUI
{
private static ImgPanelUI instance = new ImgPanelUI();
public static ComponentUI getInstance()
{
return instance;
}
public void paint(Graphics g, JComponent c)
{
System.out.println("draw ImgPanel");
ImgPanel panel = (ImgPanel) c;
g.drawImage(panel.getImg(), 0, 0, panel.getWidth(), panel.getHeight(), panel);
super.paint(g, c);
}
}
这里的paint方法只会被调用一次
