无法在JFrame上绘制 [英] can't draw on JFrame

问题描述

我正在尝试制作一个simle java程序，在鼠标定位时绘制一个圆圈，它获取鼠标X和Y坐标，但它不会绘制任何东西，我试图画一个字符串，一个圆圈和一条线但没有任何效果，我改变了一些代码，但它仍然不起作用

I'm trying to make a simle java program that draws a circle at the mouse localization, it gets the mouse X and Y coordinates but it doesn't draw anything, i tried to draw a String, a circle and a line but nothing worked, i changed the code a bit but it still doesn't works

class Test4 {

public static String a;
public static JFrame frame = new JFrame();  

 public static Point Gett(){
 PointerInfo h = MouseInfo.getPointerInfo();
 Point b = h.getLocation();
 return b;
 }

public void paintComponent(int x, int y, Graphics g) {
    g.drawOval(x, y, 10, 10);
}

public static void main(String[] args) throws InterruptedException {
    int h = 250;
    int f = 200;
    frame.setVisible(true);
    frame.setSize(h, f);
    frame.setLocationRelativeTo(null);
    while(true){
    Point b = Gett();
    int x = (int) b.getX();
    int y = (int) b.getY();
    System.out.println(x);
    System.out.println(y);
    frame.repaint();}}}

推荐答案

• 不要直接在 JFrame 上执行自定义绘画。如果可以，请始终在 JComponent 上覆盖 paintComponent 方法。

  不要为此目的使用无限循环。有 MouseMotionListener 用于鼠标移动侦听

  Don't use an infinite loop for this purpose. There is the MouseMotionListener for Mouse Motion listening

  public class Test4 {
  
      public static String a;
      public static CustomDrawingPanel content;
      public static JFrame frame = new JFrame();
      final static int OVAL_WIDTH = 10;
      final static int OVAL_HEIGHT = 10;
      static int x = -20, y = -20;
      public static MouseMotionListener listener = new ContentListener();
  
      public static void main(String[] args) throws InterruptedException {
          int h = 250;
          int f = 200;
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  
          content = new CustomDrawingPanel();
          content.addMouseMotionListener(listener);
          frame.add(content);
  
          frame.getContentPane().setPreferredSize(new Dimension(h, f));
          frame.pack();
          frame.setLocationRelativeTo(null);
  
          frame.setVisible(true);
      }
  
      //class that performs custom drawing
      static class CustomDrawingPanel extends JPanel {
  
          public void paintComponent(Graphics g) {
              super.paintComponent(g);  //Always call this
              g.drawOval(x, y, 10, 10);
          }
      }
  
      //listener to the mouse motion
      static class ContentListener implements MouseMotionListener {
  
          @Override
          public void mouseDragged(MouseEvent e) {
              mouseMoved(e); //if you delete this line, when you drag your circle will hang
          }
  
          @Override
          public void mouseMoved(MouseEvent e) {
              x = e.getX() - OVAL_WIDTH / 2;
              y = e.getY() - OVAL_HEIGHT / 2;
              content.repaint();
          }
      }
  }
  

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