addKeylistener()无法正常工作 [英] addKeylistener() not working

问题描述

对于学校来说，我必须制作一款基于Breakout的小游戏.

For school I have to make a small game which is based on Breakout.

我得到了执行此操作的JFrame:

I got my JFrame which does this:

game.setFocusable(true);
setContentpane(game);

在我的游戏中，我添加了一个输入处理程序，该输入处理程序扩展了Keylistener并实现了JPanel.

in my game I am adding a inputhandler which extends Keylistener and implements JPanel.

setFocusable(true);
Inputhandler input = new Inputhandler();
addKeylistener(input);

这似乎不起作用，我已经编写了很多测试，但是看不到让输入句柄捕获任何keyPressed.

It just doesn't seem to work, I've been writing a lot of tests but I can't see to get the input handle capture any keyPressed.

当我将JFrame更改为:

When I change my JFrame to:

add(game);

它的工作方式就像它应该工作一样，但是这样做时遇到的问题是以正确的方式绘画我的面板.我在这个问题上有些棘手，所以请有人帮帮我.

it works like it is meant to work but the problem I encounter when doing this way is painting my panels the correct way. I'm kinda stuck on this issue so please someone help me out.

我现在到达的点:

public Game(){
    setFocusable(true);
    requestFocus();
    requestFocusInWindow();

    getInputMap().put(KeyStroke.getKeyStroke("SPACE"), "pressed");
    getActionMap().put("pressed", new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Space is pressed");
        }
    });

    this.inputHandler = new InputHandler();
    addKeyListener(this.inputHandler);

    setPreferredSize(new Dimension(500,500));
}

推荐答案

如果每次问这个问题时我都有一美元，我就会退休.根据之前的类似问题...

If I had a dollar for every time this question were asked, I'd retire rich. As per previous similar questions...

• 是的，您需要使JPanel具有可聚焦性，以使其KeyListener正常工作
• 并且，您还必须将焦点放在它上面，因为集中注意力是不够的.通常，这是通过在侦听的JPanel上调用requestFocusInWindow()来实现的.
• 如果KeyListener要继续运行，没有其他任何东西可以拥有焦点或夺走焦点.
• 这是为什么我们大多数人建议反对在Swing应用程序中使用KeyListeners的几个原因之一
• 通常支持使用键绑定.

• Yes you would need to make the JPanel focusable for its KeyListener to work
• And you'd also have to give it the focus, since being focusable is not enough. Usually this is achieved by calling requestFocusInWindow() on the listened to JPanel.
• And nothing else can have the focus or steal the focus if the KeyListener is to continue functioning.
• Which is one of several reasons why most of us recommend against use of KeyListeners for Swing applications
• And usually in favor of using Key Bindings.

修改

我已经使用了您的代码，并且可以工作，无论是键绑定还是KeyListener:

I've used your code and it works, both the key bindings and the KeyListener:

import java.awt.Dimension;
import java.awt.event.*;

import javax.swing.*;

public class Game extends JPanel {
   private InputHandler inputHandler;

   public Game() {
      setFocusable(true);
      requestFocus();
      requestFocusInWindow();
      getInputMap().put(KeyStroke.getKeyStroke("SPACE"), "pressed");
      getActionMap().put("pressed", new AbstractAction() {
         @Override
         public void actionPerformed(ActionEvent e) {
            System.out.println("Space is pressed");
         }
      });
      this.inputHandler = new InputHandler();
      addKeyListener(this.inputHandler);
      setPreferredSize(new Dimension(500, 500));
   }

   class InputHandler extends KeyAdapter {
      @Override
      public void keyPressed(KeyEvent e) {
         System.out.println("key pressed");
      }

      @Override
      public void keyReleased(KeyEvent e) {
         System.out.println("key released");
      }
   }

   private static void createAndShowGui() {
      Game mainPanel = new Game();

      JFrame frame = new JFrame("Game");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_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();
         }
      });
   }
}

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