程序不是绘画 [英] Program not Painting

问题描述

我打算为此在我的JPanel上画一个正方形，但是，它没有出现。
我在做什么错了？

  class GUI扩展JPanel {
 private static Game = new Game （）; 
 ... 
 public GUI（）{
 SwingUtilities.invokeLater（new Runnable（）{
 public void run（）{
 setAttributes（）; 
 makeMenu（）; 
} 
}）; 
} 
 ... 
 public void paintComponent（Graphics g）{
 super.paintComponent（g）; 
 g.setColor（Color.white）; 
 g.drawRect（20，20，100，100）; 
 
 
 $ / code $ / pre 
 
 $ hr 
 
 
 编辑：代码 
  import javax.swing。*; 
 import java.awt。*; 
 import java.awt.event。*; 
 
类GUI扩展JPanel {
 private static Game = new Game（）; 
 
 private static JPanel panel = new JPanel（）; 
 private static JFrame frame = new JFrame（）; 
 final private static int FRAME_HEIGHT = 500; 
 final private static int FRAME_WIDTH = 500; 
 //开发板尺寸25x25px 
 final private int PIXEL_SIZE = 20; 
 public GUI（）{
 SwingUtilities.invokeLater（new Runnable（）{
 public void run（）{
 setAttributes（）; 
 makeMenu（）; 
} 
}）; 
} 
 public static void setAttributes（）{
 frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）; 
 frame.setTitle（）; 
 frame.setBackground（Color.black）; 
 frame.setVisible（true）; 
 
 
 private static void makeMenu（）{
 JButton start = new JButton（Start）; 
 start.addActionListener（new ActionListener（）{
 public void actionPerformed（ActionEvent e）{
 game.startGame（）; 
} 
}）; 
 panel.add（start）; 
 frame.add（panel）; 
 frame.pack（）; 
} 
 public void setGameFrame（）{
 panel.removeAll（）; 
 frame.setTitle（Snake v0.1）; 
 frame.setSize（FRAME_WIDTH，FRAME_HEIGHT）; 
} 
 public void paintComponent（Graphics g）{
 super.paintComponent（g）; 
 g.setColor（Color.white）; 
 g.drawRect（20，20，100，100）; 
} 
 public void paintGraphics（）{
 int [] [] pixels = Game.getGraphics（）; 
} 
} 
  
 
 
解决方案
 I看着你的代码。你在哪里添加GUI到任何东西？答：你没有，如果你不这样做，什么都不会画。解决方案：将它添加到gui中，并阅读教程，因为代码中有很多需要修复的地方。
 
 
 
其他建议：
 
 
 
 
删除所有静态变量，除了contants。
 
在主方法中调用invokeLater，而不是在JPanel的构造函数中调用
 > 
 
再次，将您的绘画图形用户界面添加到您的实际GUI中，以便将它添加到显示它的内容中。    不要调用 getGraphics（），因为它会为你提供一个非持久化的Graphics对象。 
 
 
 
 
 
 
 
例如，
 
 
  import javax.swing。*; 
 import java.awt。*; 
 
类GUI扩展JPanel {
 private static final int PREF_W = 200; 
 private static final int PREF_H = PREF_W; 
 private static final int RECT_X = 20; 
 private static final int RECT_Y = RECT_X; 
 private static final int RECT_WIDTH = 100; 
 
 public GUI（）{
 setBackground（Color.darkGray）; 
} 
 
 //使用@Override确保你的方法是一个真正的覆盖
 //注意paintComponent应该被保护，而不是public 
 @Override 
 protected void paintComponent（Graphics g）{
 super.paintComponent（g）; 
 g.setColor（Color.white）; 
 
 //在此避免魔术数字。 
 g.fillRect（RECT_X，RECT_Y，RECT_WIDTH，RECT_WIDTH）; 
 g.setColor（Color.red）; 
 g.drawRect（RECT_X，RECT_Y，RECT_WIDTH，RECT_WIDTH）; 
} 
 
 //以便布局管理员知道我想要这个JPanel有多大。 
 //这是一个愚蠢的方法实现。你希望更聪明
 @Override 
 public Dimension getPreferredSize（）{
 return new Dimension（PREF_W，PREF_H）; 
 
 
 private static void createAndShowGui（）{
 GUI mainPanel = new GUI（）; 
 
 JFrame frame = new JFrame（GUI）; 
 frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）; 
 frame.getContentPane（）。add（mainPanel）; 
 frame.pack（）; 
 frame.setLocationByPlatform（true）; 
 frame.setVisible（true）; 
 
 
 public static void main（String [] args）{
 SwingUtilities.invokeLater（new Runnable（）{
 public void run（）{
 createAndShowGui（）; 
} 
}）; 
} 
} 
  
 
I intended for this to paint a square on my JPanel, however, it does not show up.
What am I doing wrong?
class GUI extends JPanel {
    private static Game game = new Game();
    ...
    public GUI () {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                setAttributes();
                makeMenu();
            }
        });
    }
    ... 
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.white);
        g.drawRect(20, 20, 100, 100);
    }
}




Edit: the code 
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

class GUI extends JPanel {
    private static Game game = new Game();

    private static JPanel panel = new JPanel();
    private static JFrame frame = new JFrame();
    final private static int FRAME_HEIGHT = 500;
    final private static int FRAME_WIDTH = 500;
    //Board size 25x25px
    final private static int PIXEL_SIZE = 20;
    public GUI () {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            setAttributes();
            makeMenu();
         }
      });
    }
    public static void setAttributes() {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle("");
        frame.setBackground(Color.black);
        frame.setVisible(true);
    }

    private static void makeMenu() {
        JButton start = new JButton("Start");
        start.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                game.startGame();
            }
        });
        panel.add(start);
        frame.add(panel);
        frame.pack();
    }
    public void setGameFrame() {
        panel.removeAll();
        frame.setTitle("Snake v0.1");
        frame.setSize(FRAME_WIDTH, FRAME_HEIGHT);
    }
    public void paintComponent(Graphics g) {
      super.paintComponent(g);
      g.setColor(Color.white);
      g.drawRect(20, 20, 100, 100);
   }
    public void paintGraphics() {
        int[][] pixels = Game.getGraphics();
    }
}

解决方案
I looked at your code. Where do you ever add GUI to anything? Answer: you don't, and if you don't, nothing will be painted. Solution: add it to the gui, and read the tutorials as there is much to fix in your code.

Other suggestions:


Get rid of all static variables except for the contants.
Call your invokeLater in your main method, not in a JPanel's constructor
Again, add your painting GUI to your actual gui so that it gets added to something that will display it.
Don't call getGraphics() on any component as that will get you a non-persisting Graphics object.




e.g.,
import javax.swing.*;
import java.awt.*;

class GUI extends JPanel {
   private static final int PREF_W = 200;
   private static final int PREF_H = PREF_W;
   private static final int RECT_X = 20;
   private static final int RECT_Y = RECT_X;
   private static final int RECT_WIDTH = 100;

   public GUI() {
      setBackground(Color.darkGray);
   }

   // use @Override to be sure that your method is a true override
   // Note that paintComponent should be protected, not public
   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      g.setColor(Color.white);

      // avoiding "magic" numbers here.
      g.fillRect(RECT_X, RECT_Y, RECT_WIDTH, RECT_WIDTH);
      g.setColor(Color.red);
      g.drawRect(RECT_X, RECT_Y, RECT_WIDTH, RECT_WIDTH);
   }

   // so that the layout managers know how big I want this JPanel to be.
   // this is a dumb method implementation. Yours will hopefully be smarter
   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H); 
   }

   private static void createAndShowGui() {
      GUI mainPanel = new GUI();

      JFrame frame = new JFrame("GUI");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}


                        
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