密钥侦听器无法正常工作

Question

I'm really desperate. I've tried all the tips I could find, searched days in the internet and I still can't understand why can't my code work. it just doesn't respond to my keyboard input, no error message.

package drawLine;

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.*;

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class SnakeJPanel extends JPanel implements KeyListener {
    private static final long serialVersionUID = 7526472295622776147L;


JPanel panelForSnake, snake;

final int WID = 10;
final int HEI = 10;
public static int x1 = 50;
public static int y1 = 50;
public static boolean right = true, left = false, down = false, up = false;
static long millis =System.currentTimeMillis();
static long millisn =System.currentTimeMillis();


public class MyGraphics extends JComponent {

    private static final long serialVersionUID = 1L;

    MyGraphics() {
        setPreferredSize(new Dimension(1000,700));
    }


    public void paintComponent(Graphics g) {
        super.paintComponents(g);
        g.setColor(Color.red);
        g.fillOval(x1, y1, WID, HEI);
    }
}

public JPanel createContentPane (){
    JPanel totalGUI = new JPanel();
    totalGUI.setLayout(null);


    panelForSnake = new JPanel();
    panelForSnake.setBackground(Color.black);
    panelForSnake.setLocation(1,1);
    panelForSnake.setSize(1000,700);
    totalGUI.add(panelForSnake);

    MyGraphics tr = new MyGraphics();
    tr.setLocation(1,50);
    tr.setSize(1000,1000);
    panelForSnake.add(tr);

    return totalGUI;

}
private static void createAndShowGUI() {

    JFrame.setDefaultLookAndFeelDecorated(true);
    JFrame frame = new JFrame("Snake Harel");
    //Create and set up the content pane.
    SnakeJPanel demo = new SnakeJPanel();
    frame.setContentPane(demo.createContentPane());

    // The other bits and pieces that make our program a bit more stable.

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(1000, 1000);
    frame.setVisible(true);


}
public void keyPressed(KeyEvent e) {
    requestFocusInWindow();
    requestFocus();
    addKeyListener((KeyListener) this);
    setFocusable(true);
    setFocusTraversalKeysEnabled(false);
    int key = e.getKeyCode();

    if ((key == KeyEvent.VK_LEFT) && (!right)) {
        left = true;
        up = false;
        down = false;
    }

    if ((key == KeyEvent.VK_RIGHT) && (!left)) {
        right = true;
        up = false;
        down = false;
    }

    if ((key == KeyEvent.VK_UP) && (!down)) {
        up = true;
        right = false;
        left = false;
    }

    if ((key == KeyEvent.VK_DOWN) && (!up)) {
        down = true;
        right = false;
        left = false;
    }
}
public static void move(boolean l,boolean r,boolean u,boolean d){
    if (r = true){
        millis =System.currentTimeMillis();
        millisn =System.currentTimeMillis();
            while (millisn<millis+20){
                millisn=System.currentTimeMillis();
            }
        ++x1;
    }
    if (l = true){
        millis =System.currentTimeMillis();
        millisn =System.currentTimeMillis();
            while (millisn<millis+20){
                millisn=System.currentTimeMillis();
            }
        --x1;
    }
    if (u = true){
        millis =System.currentTimeMillis();
        millisn =System.currentTimeMillis();
            while (millisn<millis+20){
                millisn=System.currentTimeMillis();
            }
        ++y1;
    }
    if (d = true){
        millis =System.currentTimeMillis();
        millisn =System.currentTimeMillis();
            while (millisn<millis+20){
                millisn=System.currentTimeMillis();
            }
        --y1;
    }
}

public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
         move(left, right, up, down);
         }
    });
}

public void keyReleased(KeyEvent e) {}
public void keyTyped(KeyEvent e) {}

}

Answer 1

I've tried all the tips I could find, searched days in the internet

Then why are you still attempting to use a KeyListener??? The better solutions you will find on the forums will always tell you to use Key Bindings.

See Motion With the Keyboard for common problems with using a KeyListner and the solutions as well as working examples with Key Bindings which is what you should be using anyway.

Answer 2

You're adding the keyListener inside the keyPressed method. However, the keyPressed method is never called until the keyListener is added. Just add it in the main method or when the GUI is created.

private static void createAndShowGUI() {
    JFrame.setDefaultLookAndFeelDecorated(true);
    JFrame frame = new JFrame("Snake Harel");
    //Create and set up the content pane.
    SnakeJPanel demo = new SnakeJPanel();
    frame.setContentPane(demo.createContentPane());
    addKeyListener(this);

    // The other bits and pieces that make our program a bit more stable.

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(1000, 1000);
    frame.setVisible(true);
}

Since you're not using all of the keyListener interface I suggest creating a nested class instead and extending the KeyAdapter class.

public class ActionListener extends KeyAdapter {
    public void keyPressed(KeyEvent e) {
        int keyCode = e.getKeyCode();
        if ((key == KeyEvent.VK_LEFT) && (!right)) {
                left = true;
                up = false;
                down = false;
        }
        if ((key == KeyEvent.VK_RIGHT) && (!left)) {
            right = true;
            up = false;
            down = false;
        }
        if ((key == KeyEvent.VK_UP) && (!down)) {
            up = true;
            right = false;
            left = false;
        }
        if ((key == KeyEvent.VK_DOWN) && (!up)) {
            down = true;
            right = false;
            left = false;
        }
}

Then you'd add the ActionListener class as the key listener.

EDIT: Create an instance of the class in the main method,

new SnakeJPanel();

Then create a constructor,

private SnakeJPanel() {
    addKeyListener(this);
}