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我需要制作一个程序来打开一个图像，然后可以在它上面绘图。但是我被卡住了，因为它将我的图形返回为空。这是问题所在的代码块。如果有的话，我可以添加整个内容。

 public void paintComponent(Graphics gd) {
  // super.paintComponent(g);

super.paintComponent(gd);
//gd.drawString("This is my custom Panel!",10,20);
pencil(gd);



    }


  public void pencil(Graphics gd){
     Graphics2D g2 = (Graphics2D)gd;
  System.out.println("g2 " + g2 + "method was called");

 //g2.setColor(Color.yellow);
 //Line2D line = new Line2D();
   g2.drawLine(x1,y1,x2,y2);  
//System.out.println("pencil");


 }



  public void actionPerformed(ActionEvent e) {
  if (e.getSource() == open){
  int returnVal = fc.showOpenDialog(Lab3.this);

  if (returnVal == JFileChooser.APPROVE_OPTION) {
           File file = fc.getSelectedFile();
          try {
                    img=ImageIO.read(file);
                    ImageIcon icon=new ImageIcon(img); // ADDED
                    image.setIcon(icon); // ADDED

                    Dimension imageSize = new           Dimension(icon.getIconWidth(),icon.getIconHeight()); // ADDED
                    image.setPreferredSize(imageSize); // ADDED
                    image.add(hbar, BorderLayout.SOUTH);
                    image.add(vbar, BorderLayout.EAST);
                    image.revalidate(); // ADDED
                    image.repaint(); // ADDED
                    Graphics gd = image.getGraphics();
                }
                catch(IOException e1) {}
            }
}
 if (e.getSource() == pencil){
 try{

     System.out.println("g2" + g2);
     //pencil();
    pencil(g2);
    //g2.draw(new Ellipse2D.Double(0, 100, 30, 30));
     //g2.drawRectanlge(100,100,200,200); 
     }
 catch ( Exception err1 ) {
       System.out.println( err1.getMessage( ) );
   }
 }
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1 回答 1

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我猜你不能让图形工作

所以你需要做的是让你的画布/面板/框架从摇摆中

Canvas canvas = new Canvas();
JFrame frame = new JFrame();

frame.add(canvas);
Graphics g = canvas.getGraphics();
于 2020-03-19T15:08:33.500 回答