Swing探索：创建带图像的菜单

在Windows的“开始”菜单上，会在菜单左侧显示一幅图像。很多基于Windows的软件也有类似效果的菜单。用Java Swing可以制作出类似效果的菜单吗？答案当然是肯定的，而且非常简单。

我们首先从Swing的JPopupMenu组件进行扩展，让其接受一个图片，显示在左侧；或者接受一个字符串，动态生成图片后，在显示在左侧。为了避免准备图片的麻烦，我们就以动态生成内存图片为例，编写一个JImagedPopupMenu类。

JImagedPopupMenu在创建时可以接受一个字符串，生成一副内存图片BufferedImage。然后，我们需要覆盖JComponent的getInsets方法，重新计算Inset的left值，将其在原数值基础上加上图片的宽度，然后返回：

 public Insets getInsets() {
        Insets insets = (Insets)super.getInsets().clone();
        insets.left += imageIcon.getIconWidth();
        return insets;
    }

最后，覆盖paintComponent方法，在原基础上增加图片的绘制：
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if (imageIcon != null) {
            Insets insets = getInsets();
            g.drawImage(imageIcon.getImage(),
                        insets.left - imageIcon.getIconWidth(),
                        insets.top,
                        null);
        }
    }

完整代码如下：

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.awt.image.*;
import javax.swing.*;

public class JImagedPopupMenu extends JPopupMenu {
    private Font font = new Font("Dialog", Font.BOLD, 13);
    private ImageIcon imageIcon = null;

    public JImagedPopupMenu(ImageIcon imageIcon) {
        this.imageIcon = imageIcon;
    }

    public JImagedPopupMenu(String text) {
        this.imageIcon = createImage(text);
    }

    private ImageIcon createImage(String text) {
        BufferedImage bi = new BufferedImage(30, 1000, BufferedImage.TYPE_INT_ARGB);
        ImageIcon image = new ImageIcon(bi);
        Graphics2D g2d = bi.createGraphics();

        GradientPaint paint = new GradientPaint(0, 0, Color.yellow, 30, 10, Color.red, true);
        g2d.setPaint(paint);

        g2d.fillRect(0, 0, bi.getWidth(), bi.getHeight());

        AffineTransform at = new AffineTransform();
        at.rotate( -Math.PI / 2);

        g2d.setTransform(at);
        g2d.setColor(Color.white);
        g2d.setFont(font);
        g2d.drawString(text, -180, bi.getWidth() / 2);

        return image;
    }

    public Insets getInsets() {
        Insets insets = (Insets)super.getInsets().clone();
        insets.left += imageIcon.getIconWidth();
        return insets;
    }

    public void paint(Graphics g) {
        super.paint(g);
        if (imageIcon != null) {
            Insets insets = getInsets();
            g.drawImage(imageIcon.getImage(),
                        insets.left - imageIcon.getIconWidth(),
                        insets.top,
                        null);
        }
    }

    public static void main(String[] args) {
        final JFrame frame = new JFrame();
        frame.setSize(600, 500);
        frame.setTitle("ImageMenu");
        final JImagedPopupMenu menu = new JImagedPopupMenu("Windows XP Perfessional");
        menu.add(new JMenuItem("Winzip 8.0"));
        menu.addSeparator();
        menu.add(new JMenuItem("Programs"));
        menu.add(new JMenuItem("Document"));
        menu.add(new JMenuItem("Settings"));
        menu.add(new JMenuItem("Search"));
        menu.add(new JMenuItem("Help and Support"));
        menu.add(new JMenuItem("Run..."));
        menu.addSeparator();
        menu.add(new JMenuItem("Shut Down..."));
        JLabel label = new JLabel("Right click me to show image popup menu.");
        label.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseReleased(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    menu.show(frame, e.getPoint().x, e.getPoint().y);
                }
            }
        });
        frame.getContentPane().add(label, BorderLayout.CENTER);
        frame.show();
    }
}

运行效果如下：

同样，采用这种方法，也可以将JMenu扩展出同样的效果。