KeyListener on不起作用：Java

Question

我寫了一些代碼在屏幕上創建一個小方塊，但是當我按下左鍵時，似乎什麼也沒有發生。矩形不移動，並且「向左移動」。不會在控制檯中打印出來。這是代碼。

package game; 

import java.awt.Canvas; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics2D; 
import java.awt.event.KeyEvent; 
import java.awt.event.KeyListener; 
import java.awt.image.BufferStrategy; 

import javax.swing.JFrame; 
import javax.swing.JPanel; 

@SuppressWarnings({ "serial" }) 
public class Game extends Canvas implements Runnable, KeyListener{ 

    public static final int WIDTH = 400; 
    public static final int HEIGHT = WIDTH/12 * 9; 
    public static final int SCALE = 3; 
    public static final String NAME = "Game"; 
    //Size, scale, and name of window. 

    boolean running = false; 
    public int tickCount = 0; 

    //X and Y coordinates of the rectangle on the screen. 
    private static int rectX = 10; 
    private int rectY = 10; 

    JFrame f; 
    Canvas can; 
    BufferStrategy bs; 

    Controls c; 
public Game(){ 

    f = new JFrame(NAME); 
    f.setSize(400, 400); 
    f.setVisible(true); 
    //Sets the size of the window and makes it visible. 
    JPanel panel = (JPanel) f.getContentPane(); 
    panel.setPreferredSize(new Dimension(WIDTH, HEIGHT)); 
    panel.setLayout(null); 
    //Sets preferred size and layout to null. 
    can = new Canvas(); 
    can.setBounds(0, 0, 400, 400); 
    can.setIgnoreRepaint(true); 
    //Creates new canvas. 
    panel.add(can); 
    //Adds the canvas to the JPanel. 
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    f.pack(); 
    f.setResizable(false); 
    //Makes the window packed, nonresizable, and close the program on exit. 
    can.createBufferStrategy(3); 
    bs = can.getBufferStrategy(); 
    //Creates buffer strategy for the canvas. 
    System.out.println("Window created."); 
    addKeyListener(this); 
} 

public synchronized void start(){ 
    running = true; 
    new Thread(this).start(); 
    //Starts thread 
} 

public synchronized void stop(){ 
    running = false; 
    //For stopping the program. 
} 

public void run() { 
    long lastTime = System.nanoTime(); 
    double nsPerTick = 1000000000.0/60.0; 

    int frames = 0; 
    int ticks = 0; 
    long lastTimer = System.currentTimeMillis(); 
    double delta = 0; 
    while(running) 
    { 
     long now = System.nanoTime(); 
     delta += (now - lastTime)/nsPerTick; 
     lastTime = now; 
     boolean shouldRender = true; 
     while(delta>=1) 
     { 
     ticks++; 
     tick(); 
     delta -= 1; 
     shouldRender = true; 
     //Creates 60fps timer. Not in use. 
     } 
     try { 
      Thread.sleep(2); 
     } catch (InterruptedException e) { 
      e.printStackTrace(); 
     } 
     if(shouldRender) 
     { 
     frames++; 
     render(); 
     //Renders the image. 
     } 
     if(System.currentTimeMillis() - lastTimer >= 1000) 
     { 
      lastTimer += 1000; 
      System.out.println(frames + " frames, " + ticks + " ticks"); 
      frames = 0; 
      ticks = 0; 
      //Resets timer. Not in use. 
     } 
    } 
} 

public void tick(){ 
    tickCount++; 
    //Not in use, yet. 
} 

public void render(){ 
    Graphics2D g = (Graphics2D)bs.getDrawGraphics(); 
    //Sets g to the buffer strategy bs. 
    g.setColor(Color.BLACK); 
    g.fillRect(rectX, rectY, 100, 100); 
    //Creates black rectangle. 
    g.dispose(); 
    bs.show(); 
    //Puts the rectangle on the screen. 
} 

public static void main(String [] args){ 
    new Game().start(); 
    //Starts thread. 
} 

@Override 
public void keyTyped(KeyEvent e) { 
    // TODO Auto-generated method stub 

} 

@Override 
public void keyPressed(KeyEvent e) { 
    if(e.getKeyCode()==KeyEvent.VK_LEFT) 
    { 
     --rectX; 
     System.out.println("Move left."); 
    } 

} 

@Override 
public void keyReleased(KeyEvent e) { 
    // TODO Auto-generated method stub 

} 

}

Answer 1

因爲在構造函數中，創建一個新的畫布，而不要使用遊戲畫布和您的矩形是在新的畫布，而不是遊戲的帆布畫，讓你的聽衆有沒有影響。

請參閱以下新的構造函數，我測試了它，它工作正常。

public Game() { 

     frame = new JFrame(NAME); 
     frame.setSize(400, 400); 
     frame.setVisible(true); 
     // Sets the size of the window and makes it visible. 
     JPanel panel = (JPanel) frame.getContentPane(); 
     panel.setPreferredSize(new Dimension(WIDTH, HEIGHT)); 
     panel.setLayout(null); 
     // Sets preferred size and layout to null. 
     //can = new Canvas(); 
     //can.setBounds(0, 0, 400, 400); 
     //can.setIgnoreRepaint(true); 
     setBounds(0, 0, 400, 400); 
     setIgnoreRepaint(true); 
     // Creates new canvas. 
     panel.add(this); 
     // Adds the canvas to the JPanel. 
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
     frame.pack(); 
     frame.setResizable(false); 
     // Makes the window packed, nonresizable, and close the program on exit. 
     //can.createBufferStrategy(3); 
     createBufferStrategy(3); 
     bs = getBufferStrategy(); 
     // Creates buffer strategy for the canvas. 
     System.out.println("Window created."); 
     addKeyListener(this); 
    }