我在Java中使用KeyListener
编写了示例代码,
我创建了一个 JPanel,然后将其 focusable 设置为 true,我创建了一个 KeyListener,请求焦点,然后将 KeyListener 添加到我的面板中。但 keyListener 的方法永远不会被调用。看起来虽然我请求了焦点,但它没有焦点。
有人可以帮忙吗?
listener = new KeyLis();
this.setFocusable(true);
this.requestFocus();
this.addKeyListener(listener);
class KeyLis implements KeyListener{
@Override
public void keyPressed(KeyEvent e) {
currentver += 5;
switch (e.getKeyCode()) {
case KeyEvent.VK_LEFT : if(horizontalyInBounds()) currentPos-= 5;
break;
case KeyEvent.VK_RIGHT: if(horizontalyInBounds()) currentPos+= 5;
break;
}
repaint();
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
}
}
如果需要任何可运行的代码:
import java.awt.Color;
import java.awt.Graphics;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JLabel;
public class test extends JFrame {
private AreaOfGame areaOfGame;
public test()
{
super("");
setVisible(true);
this.setBackground(Color.darkGray);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
setLayout(null);
setBounds(200, 10, 400, 700);
areaOfGame = new AreaOfGame();
this.add(areaOfGame);
startGame();
}
public int generateNext()
{
Random r = new Random();
int n = r.nextInt(7);
return n;
}
public void startGame()
{
while(!areaOfGame.GameOver())
{
areaOfGame.startGame(generateNext());
}
}
public static void main(String[] args) {
new MainFrame();
}
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.JPanel;
public class AreaOfGame extends JPanel {
private static final int rightside = 370;
private int bottom;
private int top;
private int currentPos;
private int currentver;
private KeyLis listener;
public AreaOfGame()
{
super();
bottom = 650;
top = 50;
setLayout(null);
setBounds(20, 50, 350, 600);
setVisible(true);
this.setBackground(Color.lightGray);
listener = new KeyLis();
this.setFocusable(true);
if(this.requestFocus(true))
System.out.println("true");;
this.addKeyListener(listener);
currentPos = 150;
currentver=0;
}
public void startGame(int n)
{
while(verticallyInBound()){
System.out.println("anything");
}
}
public boolean verticallyInBound()
{
if(currentPos<= bottom -50)
return true;
return false;
}
public boolean GameOver()
{
if(top>= bottom){
System.out.println("game over");
return true;
}
else return false;
}
public boolean horizontalyInBounds()
{
if(currentPos<=rightside && currentPos>= 20)
return true;
else return false;
}
class KeyLis implements KeyListener{
@Override
public void keyPressed(KeyEvent e) {
System.out.println("called");
currentver += 5;
switch (e.getKeyCode()) {
case KeyEvent.VK_LEFT : if(horizontalyInBounds()) currentPos-= 5; break;
case KeyEvent.VK_RIGHT: if(horizontalyInBounds()) currentPos+= 5; break;
}
repaint();
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
System.out.println("called 3");
}
}
}
最佳答案
我敢打赌,您在 JPanel 渲染之前请求焦点(在顶级窗口使用 pack()
或 setVisible(true)
之前)称为),如果是这样,这将不起作用。焦点请求只有在组件渲染后才可能被授予。您是否检查过对 requestFocus()
的调用返回了什么?它必须返回 true,您的调用才有机会成功。另外,最好使用 requestFocusInWindow()
而不是 requestFocus()
。
但更重要的是,您不应该为此使用 KeyListener,而应该使用键绑定(bind),这是 Swing 本身用来响应按键的一个更高级别的概念。
编辑
SSCCE 的示例:
import java.awt.Dimension;
import java.awt.event.*;
import javax.swing.*;
public class TestKeyListener extends JPanel {
private KeyLis listener;
public TestKeyListener() {
add(new JButton("Foo")); // something to draw off focus
listener = new KeyLis();
this.setFocusable(true);
this.requestFocus();
this.addKeyListener(listener);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(300, 200);
}
private class KeyLis extends KeyAdapter {
@Override
public void keyPressed(KeyEvent e) {
switch (e.getKeyCode()) {
case KeyEvent.VK_LEFT:
System.out.println("VK_LEFT pressed");
break;
case KeyEvent.VK_RIGHT:
System.out.println("VK_RIGHT pressed");
break;
}
}
}
private static void createAndShowGui() {
TestKeyListener mainPanel = new TestKeyListener();
JFrame frame = new JFrame("TestKeyListener");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
编辑2
以及等效的 SSCCE使用键绑定(bind):
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
@SuppressWarnings("serial")
public class TestKeyBindings extends JPanel {
public TestKeyBindings() {
add(new JButton("Foo")); // something to draw off focus
setKeyBindings();
}
private void setKeyBindings() {
ActionMap actionMap = getActionMap();
int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
InputMap inputMap = getInputMap(condition );
String vkLeft = "VK_LEFT";
String vkRight = "VK_RIGHT";
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), vkLeft);
inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), vkRight);
actionMap.put(vkLeft, new KeyAction(vkLeft));
actionMap.put(vkRight, new KeyAction(vkRight));
}
@Override
public Dimension getPreferredSize() {
return new Dimension(300, 200);
}
private class KeyAction extends AbstractAction {
public KeyAction(String actionCommand) {
putValue(ACTION_COMMAND_KEY, actionCommand);
}
@Override
public void actionPerformed(ActionEvent actionEvt) {
System.out.println(actionEvt.getActionCommand() + " pressed");
}
}
private static void createAndShowGui() {
TestKeyBindings mainPanel = new TestKeyBindings();
JFrame frame = new JFrame("TestKeyListener");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(mainPanel);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}
编辑3
关于您最近的 SSCCE,您的 while (true)
循环正在阻塞您的 Swing 事件线程,并且可能会阻止用户交互或绘画的发生。最好使用 Swing 计时器,而不是 while (true)
。例如:
import java.awt.*;
import java.awt.event.*;
import java.util.Random;
import javax.swing.*;
public class BbbTest extends JFrame {
private AreaOfGame areaOfGame;
public BbbTest() {
super("");
// setVisible(true);
this.setBackground(Color.darkGray);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
setLayout(null);
setBounds(200, 10, 400, 700);
areaOfGame = new AreaOfGame();
this.add(areaOfGame);
setVisible(true);
startGame();
}
public int generateNext() {
Random r = new Random();
int n = r.nextInt(7);
return n;
}
public void startGame() {
// while (!areaOfGame.GameOver()) {
// areaOfGame.startGame(generateNext());
// }
areaOfGame.startGame(generateNext());
}
public static void main(String[] args) {
new BbbTest();
}
class AreaOfGame extends JPanel {
private static final int rightside = 370;
private int bottom;
private int top;
private int currentPos;
private int currentver;
private KeyLis listener;
public AreaOfGame() {
super();
bottom = 650;
top = 50;
setLayout(null);
setBounds(20, 50, 350, 600);
setVisible(true);
this.setBackground(Color.lightGray);
listener = new KeyLis();
this.setFocusable(true);
if (this.requestFocus(true))
System.out.println("true");
;
this.addKeyListener(listener);
currentPos = 150;
currentver = 0;
}
public void startGame(int n) {
// while (verticallyInBound()) {
// System.out.println("anything");
// }
int timeDelay = 50; // msecs delay
new Timer(timeDelay , new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
System.out.println("anything");
}
}).start();
}
public boolean verticallyInBound() {
if (currentPos <= bottom - 50)
return true;
return false;
}
public boolean GameOver() {
if (top >= bottom) {
System.out.println("game over");
return true;
}
else
return false;
}
public boolean horizontalyInBounds() {
if (currentPos <= rightside && currentPos >= 20)
return true;
else
return false;
}
class KeyLis implements KeyListener {
@Override
public void keyPressed(KeyEvent e) {
System.out.println("called");
currentver += 5;
switch (e.getKeyCode()) {
case KeyEvent.VK_LEFT:
if (horizontalyInBounds())
currentPos -= 5;
break;
case KeyEvent.VK_RIGHT:
if (horizontalyInBounds())
currentPos += 5;
break;
}
repaint();
}
@Override
public void keyReleased(KeyEvent e) {
// TODO Auto-generated method stub
}
@Override
public void keyTyped(KeyEvent e) {
System.out.println("called 3");
}
}
}
}
关于java keylistener 未调用,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/59804596/