在java中绘制线条

Question

此代码存在许多问题

public class LineEx extends JFrame implements MouseMotionListener,MouseListener{
    int x1,y1,x2,y2;
    public LineEx(){
        JLabel image=new JLabel("");
        JFileChooser chooser=new JFileChooser();

        chooser.setCurrentDirectory(new File("."));
        int r=chooser.showOpenDialog(new JFrame());
        File file=chooser.getSelectedFile();
        if(r==JFileChooser.APPROVE_OPTION){
            try {
                BufferedImage bf;
                bf = ImageIO.read(file);
                ImageIcon icon=new ImageIcon(bf);
                image.setIcon(icon);
                image.setHorizontalAlignment(JLabel.CENTER);

            } catch (IOException ex) {
                Logger.getLogger(LineEx.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
        JScrollPane jsp=new JScrollPane(image);
        getContentPane().add(jsp);
        image.addMouseListener(this);
        image.addMouseMotionListener(this);
        this.pack();
    }
    public static void main(String ar[]){
        LineEx line=new LineEx();
        line.setVisible(true);
        line.setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public void mouseClicked(MouseEvent e) {

    }

    public void mousePressed(MouseEvent e) {
        x1=e.getX();
        y1=e.getY();
    }

    public void mouseReleased(MouseEvent e) {
        JOptionPane.showMessageDialog(rootPane, "X1="+x1+"  Y1="+y1);
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }
    @Override
    public void paint(Graphics g){
        super.paintComponents(g);
        Graphics2D gd=(Graphics2D)g;
        gd.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        Line2D line=new Line2D.Double(x1,y1,x2,y2);
        gd.draw(line);
    }

    public void mouseDragged(MouseEvent e) {
        x2=e.getX();
        y2=e.getY();
        repaint();
    }

    public void mouseMoved(MouseEvent e) {
    }
}

1. MouseEvents没有获得精确的坐标,这意味着无论何时我绘制一条线,它都不在其位置上.这背后的原因是什么？
2. 当滚动条上下移动时,我想沿着图像移动线,我该怎么做？

Answer 1

• MouseEvents没有获得精确的坐标,这意味着无论何时我绘制一条线,它都不在其位置上.这背后的原因是什么？
• 当滚动条上下移动时,我想沿着图像移动线,我该怎么做？

你正在从中得到正确的坐标JLabel但是在上面画上了JFrame.框架坐标从左上角开始,"包括"窗口标题/边框.

覆盖paintComponent方法,JLabel它将获得正确的插入和坐标.

例:

class ImageComponent extends JComponent 
        implements MouseListener, MouseMotionListener {
    private final BufferedImage img;
    private Point p1, p2;

    public ImageComponent(URL url) throws IOException {
        img = ImageIO.read(url);
        setPreferredSize(new Dimension(img.getWidth(), img.getHeight()));
        addMouseListener(this);
        addMouseMotionListener(this);
    }
    @Override protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(img, 0, 0, img.getWidth(), img.getHeight(), this);
        if (p1 != null && p2 != null)
            g.drawLine(p1.x, p1.y, p2.x, p2.y);
    }
    @Override public void mousePressed(MouseEvent e) {
        p1 = e.getPoint();
    }
    @Override public void mouseDragged(MouseEvent e) {
        mouseReleased(e);
    }
    @Override public void mouseReleased(MouseEvent e) {
        p2 = e.getPoint();
        repaint();
    }
    @Override public void mouseMoved(MouseEvent e) {}
    @Override public void mouseClicked(MouseEvent e) {}
    @Override public void mouseEntered(MouseEvent e) {}
    @Override public void mouseExited(MouseEvent e) {}
}

测试代码(生成此屏幕截图):

public static void main(String[] args) throws Exception {

    final URL lenna =
        new URL("http://upload.wikimedia.org/wikipedia/en/2/24/Lenna.png");

    final ImageComponent image = new ImageComponent(lenna);

    JFrame frame = new JFrame("Test");
    frame.add(new JScrollPane(image));

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 300);
    frame.setVisible(true);
}