英文:
How to use KeyEvents Listener in Java for KeyPressed
问题
Window
package com.landminegame.main;
import java.awt.*;
import javax.swing.JFrame;
public class Window extends Canvas {
private static final long serialVersionUID = -240840600533728354L;
public static void main (String args[]) {
JFrame frame = new JFrame("Landmine Game!");
KeyPanel panel = new KeyPanel();
panel.setFocusable(true);
panel.addKeyListener(new KeyPressedKeyListener(panel));
panel.setOpaque(false);
frame.setSize(500, 500);
frame.getContentPane().add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
KeyPressedKeyListener
package com.landminegame.main;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class KeyPressedKeyListener implements KeyListener {
private KeyPanel panel;
public KeyPressedKeyListener(KeyPanel panel) {
this.panel = panel;
}
@Override
public void keyTyped(KeyEvent keyEvent) {
}
@Override
public void keyPressed(KeyEvent keyEvent) {
if (keyEvent.getKeyCode() == KeyEvent.VK_LEFT) {
panel.LeftKey();
};
if (keyEvent.getKeyCode() == KeyEvent.VK_RIGHT) {
panel.RightKey();
};
if (keyEvent.getKeyCode() == KeyEvent.VK_UP) {
panel.UpKey();
};
if (keyEvent.getKeyCode() == KeyEvent.VK_DOWN) {
panel.DownKey();
};
}
@Override
public void keyReleased(KeyEvent keyEvent) {
}
}
KeyPanel
package com.landminegame.main;
import javax.swing.*;
import java.awt.*;
public class KeyPanel extends JPanel {
public Rectangle mover = new Rectangle(56, 305, 40, 40);
private int [][] board = {
{1, 1, 1, 1, 1, 1, 1, 1},
{1, 0, 3, 3, 0, 3, 4, 1},
{1, 0, 3, 3, 3, 0, 3, 1},
{1, 3, 3, 0, 3, 3, 0, 1},
{1, 0, 3, 0, 3, 0, 0, 1},
{1, 3, 0, 3, 0, 0, 0, 1},
{1, 2, 3, 0, 3, 0, 0, 1},
{1, 1, 1, 1, 1, 1, 1, 1}
};
public void paint(Graphics g) {
super.paint(g);
g.translate(28, 25);
for (int row = 0; row < board.length; row++) {
for (int col = 0; col < board[0].length; col++) {
Color color = Color.WHITE;
switch (board[row][col]) {
case 1 : color = Color.BLACK; break;
case 2 : color = Color.YELLOW; break;
case 4 : color = Color.RED;
}
g.setColor(color);
g.fillRect(50*col, 50 * row, 50, 50);
g.setColor(Color.BLACK);
g.drawRect(50*col, 50*row, 50, 50);
}
}
g.setColor(Color.GREEN);
g.fillRect(mover.x, mover.y, mover.width, mover.height);
}
public void LeftKey() {
mover.x -= 40;
this.repaint();
}
public void RightKey() {
mover.x += 40;
this.repaint();
}
public void UpKey() {
mover.y -= 40;
this.repaint();
}
public void DownKey() {
mover.y += 40;
this.repaint();
}
}
这是你的整个程序。如果有任何帮助,谢谢!
英文:
I am a newbie to Java and I have been working on a landmine game. I finished the board and the key events but the key events are not working. I am not sure what I am doing wrong. I have shown the code below. I used some help from Youtube from the following video: https://www.youtube.com/watch?v=7kMXr2AJLPA
Window
package com.landminegame.main;
import java.awt.*;
import javax.swing.JFrame;
public class Window extends Canvas {
private static final long serialVersionUID = -240840600533728354L;
public static void main (String args[]) {
JFrame frame = new JFrame("Landmine Game!");
KeyPanel panel = new KeyPanel();
panel.setFocusable(true);
panel.addKeyListener(new KeyPressedKeyListener(panel));
panel.setOpaque(false);
frame.setSize(500, 500);
frame.getContentPane().add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setResizable(false);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
KeyPressedKeyListener
package com.landminegame.main;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
public class KeyPressedKeyListener implements KeyListener {
private KeyPanel panel;
public KeyPressedKeyListener(KeyPanel panel) {
this.panel = panel;
}
@Override
public void keyTyped(KeyEvent keyEvent) {
}
@Override
public void keyPressed(KeyEvent keyEvent) {
if (keyEvent.KEY_PRESSED == KeyEvent.VK_LEFT) {
panel.LeftKey();
};
if (keyEvent.KEY_PRESSED == KeyEvent.VK_RIGHT) {
panel.RightKey();
};
if (keyEvent.KEY_PRESSED == KeyEvent.VK_UP) {
panel.UpKey();
};
if (keyEvent.KEY_PRESSED == KeyEvent.VK_DOWN) {
panel.DownKey();
};
}
@Override
public void keyReleased(KeyEvent keyEvent) {
}
}
KeyPanel
package com.landminegame.main;
import javax.swing.*;
import java.awt.*;
public class KeyPanel extends JPanel {
public Rectangle mover = new Rectangle(56, 305, 40, 40);
private int [][] board = {
{1, 1, 1, 1, 1, 1, 1, 1},
{1, 0, 3, 3, 0, 3, 4, 1},
{1, 0, 3, 3, 3, 0, 3, 1},
{1, 3, 3, 0, 3, 3, 0, 1},
{1, 0, 3, 0, 3, 0, 0, 1},
{1, 3, 0, 3, 0, 0, 0, 1},
{1, 2, 3, 0, 3, 0, 0, 1},
{1, 1, 1, 1, 1, 1, 1, 1}
};
public void paint(Graphics g) {
super.paint(g);
g.translate(28, 25);
for (int row = 0; row < board.length; row++) {
for (int col = 0; col < board[0].length; col++) {
Color color = Color.WHITE;
switch (board[row][col]) {
case 1 : color = Color.BLACK; break;
case 2 : color = Color.YELLOW; break;
case 4 : color = Color.RED;
}
g.setColor(color);
g.fillRect(50*col, 50 * row, 50, 50);
g.setColor(Color.BLACK);
g.drawRect(50*col, 50*row, 50, 50);
}
}
g.setColor(Color.GREEN);
g.fillRect(mover.x, mover.y, mover.width, mover.height);
}
public void LeftKey() {
mover.x -= 40;
this.repaint();
}
public void RightKey() {
mover.x += 40;
this.repaint();
}
public void UpKey() {
mover.y += 40;
this.repaint();
}
public void DownKey() {
mover.y -= 40;
this.repaint();
}
}
This is my whole program. Any help is appreciated, thank you!
答案1
得分: 2
使用KeyListener
到JPanel
是行不通的。你将不得不改用KeyBindings。例如:
panel.getInputMap().put(KeyStroke.getKeyStroke("LEFT"), "left");
panel.getActionMap().put("left", new AbstractAction() {
@Override
public void actionPerformed(ActionEvent e) {
System.out.println("按下了左键");
}
});
然而,这些匿名的AbstractAction
类让我感到烦恼。这就是为什么我会做类似这样的事情:
public class RunnableAction extends AbstractAction {
private Runnable action;
public RunnableAction(Runnable action) {
this.action = action;
}
@Override
public void actionPerformed(ActionEvent e) {
action.run();
}
}
然后:
panel.getInputMap().put(KeyStroke.getKeyStroke("LEFT"), "left");
panel.getActionMap().put("left", new RunnableAction(panel::LeftKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("RIGHT"), "right");
panel.getActionMap().put("right", new RunnableAction(panel::RightKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("DOWN"), "down");
panel.getActionMap().put("down", new RunnableAction(panel::DownKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("UP"), "up");
panel.getActionMap().put("up", new RunnableAction(panel::UpKey));
不过,我建议你尝试遵循标准的命名约定。例如,方法应该以小写字母开头(panel.UpKey()
应改为 panel.upKey()
等)
最后,你不必将main
方法放在一个继承自Canvas
的类中。这是完全没有意义的。
英文:
Using a KeyListener
to a JPanel
is not going to work. You will have to use KeyBindings instead. For example:
panel.getInputMap().put(KeyStroke.getKeyStroke("LEFT"), "left");
panel.getActionMap().put("left", new AbstractAction() {
@Override
public void actionPerformed(ActionEvent e) {
System.out.println("left key is pressed");
}
});
However, these anonymous AbstractAction
classes annoy me. That's why I would do something like that:
public class RunnableAction extends AbstractAction {
private Runnable action;
public RunnableAction(Runnable action) {
this.action = action;
}
@Override
public void actionPerformed(ActionEvent e) {
action.run();
}
}
And then:
panel.getInputMap().put(KeyStroke.getKeyStroke("LEFT"), "left");
panel.getActionMap().put("left", new RunnableAction(panel::LeftKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("RIGHT"), "right");
panel.getActionMap().put("right", new RunnableAction(panel::RightKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("DOWN"), "down");
panel.getActionMap().put("down", new RunnableAction(panel::DownKey));
panel.getInputMap().put(KeyStroke.getKeyStroke("UP"), "up");
panel.getActionMap().put("up", new RunnableAction(panel::UpKey));
However, I suggest you to try following the standard naming conventions. For example, methods should start with lower case. (panel.UpKey()
should be panel.upKey()
, etc)
Finally you do not have to have your main
method in a class that extends Canvas
. This is totally pointless.
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