JFrame setText() 中的 JLabel 问题

Question

我是一名新手编码员，当我在处理一个包含 JFrame、JPanel 和 JLabel 的项目时，我遇到了一些奇怪的问题，即 JLabel 出现在两个地方，我将它设置为在顶部 -框架的左角，而不是它应该在的位置。

这是代码的基本大纲：

import java.awt.event.*;     // for key listener
import java.awt.*;         

import javax.swing.JFrame; 
import javax.swing.JLabel;
import javax.swing.BoxLayout;
import javax.swing.*;

import java.util.Random;

public class Game extends JFrame {



   JFrame Game;
   JLabel label;
   GamePanel panel;   // GamePanel class is the panel class that extends JPanel

   public Game(String title) {

      super(title);
      this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      this.setSize(420 + 110,420 + 220);
      this.setLocationRelativeTo(null); 
      this.setLayout(new BoxLayout(this.getContentPane(), BoxLayout.Y_AXIS));
      this.setResizable(false);

      label = new JLabel("Score : " + score);
      label.setAlignmentX(JLabel.CENTER_ALIGNMENT);
      label.setAlignmentY(JLabel.CENTER_ALIGNMENT);

      panel = new GamePanel(..appropriate variables);

      this.add(panel);
      this.add(label);
      this.add(Box.createRigidArea(new Dimension(0,50)));

      panel.setFocusable(true);
      panel.addKeyListener(new KeyHandler());

   }

   // some variables..


   class KeyHandler extends KeyAdapter {

      public void keyPressed(KeyEvent e)
      {
         int keycode = e.getKeyCode(); 

         switch(keycode) {

             //cases for arrow keys, which will update the variable that panel uses

         }

         //some other tasks for the game..

         panel.updateVariables(...appropriate variables to update);
         panel.repaint();
         label.setText("Score : " + score);

      }

   }

   public static void main(String [] args)  {

      Game me = new Game("GAME");        

      me.setVisible(true);


   }

}   

所以问题的总结是，每当 setText 实际更新标签时，标签似乎出现在两个地方：JFrame 的左上角和我指定它显示的位置。有趣的是，左上角的“buggy”标签也会随着真实标签的更新而更新。

提前致谢！

编辑：这是 GamePanel 的布局。

import javax.swing.JPanel;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Color;
import java.awt.Rectangle;
import java.awt.BasicStroke;

public class GamePanel extends JPanel
{      

   // some variables..

   // setXxx methods for corresponding variables

   void drawCursor(int x, int y)
   {
      //draws thicker rectangle around the selected position
      //uses setStroke, setColor, and draw(Rectangle)
   }

   public void paintComponent( Graphics g )   
   {
      Graphics2D g2 = (Graphics2D) g;         

      for(int i = 0; i < size; i++) {

         for(int j = 0; j < size; j++) {

            switch(gameGrid[j][i]) {   // I have an array grid[][] that has information of which color goes into the specific position of the grid

               // each case will setColor the corresponding color and use g2.fill(new Rectangle(...));
               case 0:
                  g2.setColor(...);
                  g2.fill(new Rectangle(...));
                  break;
               // and so on

            }
            g2.setColor(Color.BLACK);
            g2.draw(new Rectangle(50 + (j * 420/size), 50 + (i * 420/size), 420/size,420/size));         
         }    
      }
      drawCursor(x, y);
   }
}

Answer 1

正如我在我的 cmets 中所说，您正在覆盖 paintComponent（在 GamePanel 中）但没有调用 super.paintComponent...

public void paintComponent( Graphics g )   
{
    Graphics2D g2 = (Graphics2D) g;   
    for(int i = 0; i < size; i++) { 

Graphics 是一个共享资源，用于绘制在给定绘制周期内更新的所有组件的内容，这意味着，当您收到对Graphics 上下文的引用时，它仍然具有画在你面前的“东西”。 paintComponent 的工作之一就是清除上下文准备绘画

在进行任何自定义绘画之前，请致电 super.paintComponent(g);

public void paintComponent( Graphics g )   
{
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g;   
    for(int i = 0; i < size; i++) { 

查看Painting in AWT and Swing 和Performing Custom Painting 了解如何在 Swing 中绘画的详细信息