Swing探索：創建帶圖像的菜單

在Windows的“開始”菜單上，會在菜單左側顯示一幅圖像。很多基於Windows的軟件也有類似效果的菜單。用Java Swing可以製作出類似效果的菜單嗎？答案當然是肯定的，而且非常簡單。

我們首先從Swing的JPopupMenu組件進行擴展，讓其接受一個圖片，顯示在左側；或者接受一個字符串，動態生成圖片後，在顯示在左側。爲了避免準備圖片的麻煩，我們就以動態生成內存圖片爲例，編寫一個JImagedPopupMenu類。

JImagedPopupMenu在創建時可以接受一個字符串，生成一副內存圖片BufferedImage。然後，我們需要覆蓋JComponent的getInsets方法，重新計算Inset的left值，將其在原數值基礎上加上圖片的寬度，然後返回：

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

最後，覆蓋paintComponent方法，在原基礎上增加圖片的繪製：
    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);
        }
    }

完整代碼如下：

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();
    }
}

運行效果如下：

同樣，採用這種方法，也可以將JMenu擴展出同樣的效果。