Question

我无法让我的JMenuBar与paint（）方法一起出现。

package Main;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;

public class Main extends JFrame{

int x, y; // axis position for oval

//JMenuBar Variables
JMenuBar menuBar;
JMenu file;
JMenuItem newGame;
JMenuItem checkScore;
JMenuItem exitGame;

// DOUBLE BUFFERING
private Image dbImage;
private Graphics dbGraphics;

Font font = new Font("Arial", Font.ITALIC, 30);

// KeyListener Class
public class KeyListener extends KeyAdapter {
    public void keyPressed(KeyEvent e){
        int keyCode = e.getKeyCode();
        if(keyCode == e.VK_LEFT){
            if(x <=0){ // FRAME COLLISION DETECTION 
                x=0;
            }else
            x += -5; //decrement position to the left 
        }
        if(keyCode == e.VK_RIGHT){
            if(x >= 380){
                x = 380;
            }else
            x += +5; //incrementing position to the right
        }
        if(keyCode == e.VK_UP){
            if (y <= 25){
                y = 25;
            }else
            y += -5; //decrementing position up
        }
        if(keyCode == e.VK_DOWN){
            if(y >= 380){
                y = 380;
            }else
            y += +5; //incrementing position down
        }
    }
}


// CONSTRUCTOR
public Main(){
// Window Properties
    addKeyListener(new KeyListener()); // creates instance of KeyListener class
    setTitle("Tower Defence");
    setSize(400, 400);
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    //setBackground(Color.CYAN);


// JMenuBar
    menuBar = new JMenuBar();
    file = new JMenu("File");
    newGame = new JMenuItem("New Game");
    checkScore = new JMenuItem("Check High Scores");
    exitGame = new JMenuItem("Close Game");

    menuBar.add(file);
    file.add(newGame);
    file.add(checkScore);
    file.addSeparator();
    file.add(exitGame);
    setJMenuBar(menuBar);

// Display frame after all components added
    setVisible(true);

// default position for oval
    x = 150;
    y = 150;

}


public void paint(Graphics g){
    dbImage = createImage(getWidth(), getHeight()); // creates image of screen
    dbGraphics = dbImage.getGraphics(); // gets graphics to be drawn in off screen image
    paintComponent(dbGraphics); // paints graphics
    g.drawImage(dbImage, 0, 0, this);  // draw image to the visible screen
}

    // PAINT GRAPHICS TO SCREEN
public void paintComponent(Graphics g){

    g.setFont(font);
    g.drawString("Hello World", 100, 200);

    g.setColor(Color.red);
    g.drawOval(x, y, 15, 15);
    g.fillOval(x, y, 15, 15);
    repaint();
}


// MAIN METHOD
public static void main(String[] args) {
    new Main();
}

}

我看到了一个不同的问题，解决方案是覆盖paint方法并添加super.paint（g）; 当我尝试这个时，JMenuBar会出现但框架会不断闪烁。

Answer 1

不要不必要地延长JFrame
不要在JFrame的任何绘图方法上覆盖不必要的添加Jpanel并覆盖paintComponent
不要在repaint(...)中调用paintComponent(...)，因为这会导致循环，即重新调用将重新调用paintComponent并且循环将继续
在Event Dispatch Thread
请勿在{{1}}上致电setSize(..)，而是覆盖JFrame并返回适合所有图纸的合适尺寸，然后在设置getPreferredSize之前致电JFrame#pack()可见
不要将JFrame / KeyListener用于Swing组件而是使用KeyBindings

以下是您的代码修复：

enter image description here

KeyAdapter

Answer 2

哎呀，我会把我的代码扔进戒指。根据我的评论记录。另外，不要使用KeyListeners，而是使用Key Bindings。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.RenderingHints;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.*;

@SuppressWarnings("serial")
public class Main2 extends JPanel {
   private static final int PREF_W = 400;
   private static final int PREF_H = PREF_W;
   private static final int OVAL_W = 15;
   private int x = 150;
   private int y = 150;
   private JMenuBar menuBar;
   private JMenu file;
   private JMenuItem newGame;
   private JMenuItem checkScore;
   private JMenuItem exitGame;
   private Font font = new Font("Arial", Font.ITALIC, 30);

   public Main2() {      
      menuBar = new JMenuBar();
      file = new JMenu("File");
      newGame = new JMenuItem("New Game");
      checkScore = new JMenuItem("Check High Scores");
      exitGame = new JMenuItem("Close Game");

      menuBar.add(file);
      file.add(newGame);
      file.add(checkScore);
      file.addSeparator();
      file.add(exitGame);

      addKeyBinding();
   }

   public JMenuBar getMenuBar() {
      return menuBar;
   }

   @Override
   public Dimension getPreferredSize() {
      return new Dimension(PREF_W, PREF_H);
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
            RenderingHints.VALUE_ANTIALIAS_ON);
      g2.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING, 
            RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
      g.setFont(font);
      g.drawString("Hello World", 100, 200);

      g.setColor(Color.red);
      g.drawOval(x, y, OVAL_W, OVAL_W);
      g.fillOval(x, y, OVAL_W, OVAL_W);
   }

   private void addKeyBinding() {
      int condition = WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();

      for (final MyDirection dir : MyDirection.values()) {
         KeyStroke keyStroke = KeyStroke.getKeyStroke(dir.getKeyCode(), 0);
         inputMap.put(keyStroke, dir.toString());
         actionMap.put(dir.toString(), new AbstractAction() {

            @Override
            public void actionPerformed(ActionEvent evt) {
               int newX = x + dir.getxTrans();
               int newY = y + dir.getyTrans();

               newX = Math.min(newX, PREF_W - 2 * OVAL_W);
               newX = Math.max(newX, OVAL_W);
               newY = Math.min(newY, PREF_H - 2 * OVAL_W);
               newY = Math.max(newY, OVAL_W);

               x = newX;
               y = newY;
               repaint();
            }
         });
      }
   }

   enum MyDirection {
      UP(KeyEvent.VK_UP, 0, -5), DOWN(KeyEvent.VK_DOWN, 0, 5), 
      LEFT(KeyEvent.VK_LEFT, -5, 0), RIGHT(KeyEvent.VK_RIGHT, 5, 0);

      private int keyCode;
      private int xTrans;
      private int yTrans;

      private MyDirection(int keyCode, int xTrans, int yTrans) {
         this.keyCode = keyCode;
         this.xTrans = xTrans;
         this.yTrans = yTrans;
      }

      public int getKeyCode() {
         return keyCode;
      }

      public int getxTrans() {
         return xTrans;
      }

      public int getyTrans() {
         return yTrans;
      }


   }

   private static void createAndShowGui() {
      Main2 main = new Main2();

      JFrame frame = new JFrame("Main2");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(main);
      frame.setJMenuBar(main.getMenuBar());
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

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

JMenuBar用油漆方法

2 个答案: