KeyListener方法keyPressed不工作
KeyListener方法keyPressed不工作
提问于 2020-04-25 13:18:39
我正在尝试用java swing做一个小游戏，并且已经取得了相当大的进展，但是现在我的KeyListener没有使用keyPressed方法。
下面是我的一些代码
public class Screen extends JPanel implements Runnable{
private static final int WIDTH = 300, HEIGHT = 300, RIGHT = 0, LEFT = 1, UP = 2, DOWN = 3, STILL = 4;
private Thread thread;
private boolean running = false;
private int direction = DOWN;
public Screen() {
setFocusable(true);
addKeyListener(new Key());
setPreferredSize(new Dimension(WIDTH, HEIGHT));
start();
}
public void tick(){
System.out.println(direction)
}
public void start() {
running = true;
thread = new Thread(this, "Game Loop");
thread.start();
}
public void run() {
while (running) {
tick();
repaint();
}
}
private class Key implements KeyListener{
@Override
public void keyTyped(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
if (key == KeyEvent.VK_D) {
direction = RIGHT;
}
if (key == KeyEvent.VK_A) {
direction = LEFT;
}
if (key == KeyEvent.VK_W) {
direction = UP;
}
if (key == KeyEvent.VK_S) {
direction = DOWN;
}
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
}
}我正在查看控制台，并期望输出从3(按下)变为我按下的任何按钮，但它永远不会改变。过了一段时间后，我意识到keyPressed方法有问题，我只是不知道是什么问题。
回答 2
Stack Overflow用户
发布于 2020-04-25 15:04:02
你不需要单独的“游戏循环”线程。Swing是事件驱动的。当用户按下计算机键盘上的某个键时，将调用您的按键侦听器代码。
正如MadProgrammer在他的comment to your question中提到的
在EDT上下文之外修改UI的状态可能会导致绘画问题
换句话说，Swing是single threaded的，这个线程被称为事件分派线程( Event Dispatch thread，EDT )，所有更改图形用户界面的代码都应该只在事件分派线程上执行。
下面的代码是一个独立的Swing应用程序，它显示一个可聚焦的JPanel。当您按下键盘上的一个相关“方向”键时，即A或D或S或W，控制台将显示方向。按下任何其他键时，方向仍会写入控制台。请注意，我对各个方向使用了enum，而不是整数常量。
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;
public class Screen01 extends JPanel implements Runnable {
public enum Directions {RIGHT, LEFT, UP, DOWN, STILL};
private static final int WIDTH = 300, HEIGHT = 300;
private Directions direction;
public Screen01() {
setPreferredSize(new Dimension(WIDTH, HEIGHT));
setFocusable(true);
addKeyListener(new Key());
}
public void run() {
createAndDisplayGui();
}
private void createAndDisplayGui() {
JFrame frame = new JFrame("Screen");
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.add(this, BorderLayout.CENTER);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
private class Key implements KeyListener {
@Override
public void keyTyped(KeyEvent e) {
// Do nothing.
}
@Override
public void keyPressed(KeyEvent e) {
int key = e.getKeyCode();
switch (key) {
case KeyEvent.VK_D:
direction = Directions.RIGHT;
break;
case KeyEvent.VK_A:
direction = Directions.LEFT;
break;
case KeyEvent.VK_W:
direction = Directions.UP;
break;
case KeyEvent.VK_S:
direction = Directions.DOWN;
break;
default:
direction = Directions.STILL;
}
System.out.println("Direction = " + direction);
}
@Override
public void keyReleased(KeyEvent e) {
// Do nothing.
}
}
public static void main(String[] args) {
EventQueue.invokeLater(new Screen01());
}
}Stack Overflow用户
发布于 2020-04-26 07:51:19
利用key bindings API，它将解决这个和所有其他与KeyListener相关的问题，而不会有太多的黑客攻击，也不会弄清楚为什么它“有时”会工作
Swing是单线程的。这意味着您在从事件分派线程的上下文之外(直接或间接)更新UI的状态时应格外小心，这也包括UI可能依赖的任何状态。
有关更多详细信息，请查看Concurrency in Swing。
在没有更多细节的情况下，最简单的解决方案之一是使用Swing Timer作为主要的“勾选”操作。每当它“滴答作响”时，您将检查输入的状态，更新模型的状态，并触发重新绘制来更新UI
例如..。
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.util.HashSet;
import java.util.Set;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
public class Main {
public static void main(String[] args) {
new Main();
}
public Main() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame();
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public static class TestPane extends JPanel {
enum Input {
UP, DOWN, LEFT, RIGHT
}
private Set<Input> input = new HashSet<>();
public TestPane() {
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "Left.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "Left.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, false), "Right.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "Right.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false), "Up.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true), "Up.released");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, false), "Down.pressed");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, true), "Down.released");
am.put("Left.pressed", new InputAction(Input.LEFT, input, false));
am.put("Left.released", new InputAction(Input.LEFT, input, true));
am.put("Right.pressed", new InputAction(Input.RIGHT, input, false));
am.put("Right.released", new InputAction(Input.RIGHT, input, true));
am.put("Down.pressed", new InputAction(Input.DOWN, input, false));
am.put("Down.released", new InputAction(Input.DOWN, input, true));
am.put("Up.pressed", new InputAction(Input.UP, input, false));
am.put("Up.released", new InputAction(Input.UP, input, true));
input.add(Input.UP);
input.add(Input.DOWN);
input.add(Input.LEFT);
input.add(Input.RIGHT);
Timer timer = new Timer(5, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
// Check what's currently been pressed
// and update the state accordingly...
if (input.contains(Input.UP)) {
//..
}
if (input.contains(Input.DOWN)) {
//..
}
if (input.contains(Input.LEFT)) {
//..
}
if (input.contains(Input.RIGHT)) {
//..
}
repaint();
}
});
timer.start();
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
int midX = getWidth() / 2;
int midY = getHeight() / 2;
FontMetrics fm = g2d.getFontMetrics();
int spaceWidth = fm.stringWidth("M");
int spaceHeight = fm.getHeight();
if (input.contains(Input.UP)) {
String text = "UP";
g2d.drawString(text,
midX - (fm.stringWidth(text)) / 2,
(midY - (spaceHeight * 2) + fm.getAscent()));
}
if (input.contains(Input.DOWN)) {
String text = "DOWN";
g2d.drawString(text,
midX - (fm.stringWidth(text)) / 2,
(midY + spaceHeight + fm.getAscent()));
}
if (input.contains(Input.LEFT)) {
String text = "LEFT";
g2d.drawString(text,
(midX - spaceWidth - fm.stringWidth(text)),
(midY + (fm.getAscent() / 2)));
}
if (input.contains(Input.RIGHT)) {
String text = "RIGHT";
g2d.drawString(text,
(midX + spaceWidth),
(midY + (fm.getAscent() / 2)));
}
g2d.dispose();
}
public class InputAction extends AbstractAction {
private Input input;
private Set<Input> inputSet;
private boolean onRelease;
public InputAction(Input input, Set<Input> inputSet, boolean onRelease) {
this.input = input;
this.inputSet = inputSet;
this.onRelease = onRelease;
}
@Override
public void actionPerformed(ActionEvent e) {
if (onRelease) {
inputSet.remove(input);
} else {
inputSet.add(input);
}
}
}
}
}这是一个基本的示例，它直接在paintComponent方法中打印按键输入的状态。更实际的实现是使用Timer的ActionListener来检查input状态，并相应地更改所需的模型，如示例中所暗示的那样。
如果您需要更直接的控制，那么您需要避免使用Swing绘画系统，而是自己进行控制。为此，您需要使用BufferStrategy。这是一个更复杂的解决方案，但它也更强大，因为您可以完全控制何时更新UI
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/61421299
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