用Java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。为了避免预备图片的麻烦，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 ImageMenu extends JPopupMenu {

??? private Font font = new Font("Dialog", Font.BOLD, 13);

??? private ImageIcon imageIcon = null;

??? public ImageMenu(ImageIcon imageIcon) {

??????? this.imageIcon = imageIcon;

??? }

??? public ImageMenu(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();