如何在 java 中向我的 Gui 添加 keylistener

Question

我有一个简单的 Gui

public Gui(){
    ablak = new JFrame("Snake game");
    ablak.setVisible(true);
    ablak.setSize(new Dimension(600,600));
    ablak.setFocusable(true);
    ablak.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    ablak.add(new Grid());
    ablak.add(new Key());
}

还有一个关键类来监听关键事件

package snake;

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

public class Key implements KeyListener {

    @Override
    public void keyPressed(KeyEvent e) {
        if(e.getKeyCode() == KeyEvent.VK_UP){
            System.out.println("Hi");
        }
    }

    @Override
    public void keyTyped(KeyEvent e) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }

    @Override
    public void keyReleased(KeyEvent e) {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
    }


}

如您所见，按向上箭头键应该会说类似 Hi，但没有任何反应。 如果我尝试在 Gui 类中添加(new Key())，则会出现错误。 我做错了什么？

谢谢

Answer 1

你需要使用addKeyListener()方法：

public class Test2 {
    public static void main(String[] args) {
        JFrame ablak = new JFrame("Snake game");
        ablak.setVisible(true);
        ablak.setSize(new Dimension(600,600));
        ablak.setFocusable(true);
        ablak.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        ablak.addKeyListener(new KeyListener(){
             @Override
                public void keyPressed(KeyEvent e) {
                    if(e.getKeyCode() == KeyEvent.VK_UP){
                        System.out.println("Hi");
                    }
                }

                @Override
                public void keyTyped(KeyEvent e) {
                    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
                }

                @Override
                public void keyReleased(KeyEvent e) {
                    throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
                }
        });
        ablak.setVisible(true);
    }
}

Answer 2

您需要先阅读教程。您不要使用 add(...) 添加 KeyListeners 而是使用 addKeyListener(...) 因为 add(...) 仅用于添加 component ，但话虽如此，我什至不会为此使用 KeyListener 而是当焦点阻止您的 KeyListener 工作时，键绑定将有助于解决您将来会遇到的问题。

Key Bindings tutorial Link

---

例如，用我的小键绑定添加编译和运行 Kevin Bowersox 的程序：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Test2 {
   public static void main(String[] args) {
      JFrame ablak = new JFrame("Snake game");
      ablak.setVisible(true);
      ablak.setSize(new Dimension(600, 600));
      ablak.setFocusable(true);
      ablak.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      ablak.addKeyListener(new KeyAdapter() {
         @Override
         public void keyPressed(KeyEvent e) {
            if (e.getKeyCode() == KeyEvent.VK_UP) {
               System.out.println("Hi from KeyListener");
            }
         }
      });
      ablak.setVisible(true);

      JPanel contentPane = (JPanel) ablak.getContentPane();
      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = contentPane.getInputMap(condition);
      ActionMap actionMap = contentPane.getActionMap();

      String down = "down";
      inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), down);
      actionMap.put(down, new AbstractAction() {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            System.out.println("Hi from Key Binding");
         }
      });

   }
}

如果您运行它并按下向上和向下箭头，您将看到来自功能正常的 KeyListener 和 Key Bindings 的响应。

但是如果你像这样添加一个 JButton 会怎样：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Test2 {
   public static void main(String[] args) {
      JFrame ablak = new JFrame("Snake game");
      ablak.setVisible(true);
      ablak.setSize(new Dimension(600, 600));
      ablak.setFocusable(true);
      ablak.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      ablak.addKeyListener(new KeyAdapter() {
         @Override
         public void keyPressed(KeyEvent e) {
            if (e.getKeyCode() == KeyEvent.VK_UP) {
               System.out.println("Hi from KeyListener");
            }
         }
      });

      JPanel contentPane = (JPanel) ablak.getContentPane();
      int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = contentPane.getInputMap(condition);
      ActionMap actionMap = contentPane.getActionMap();

      String down = "down";
      inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), down);
      actionMap.put(down, new AbstractAction() {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            System.out.println("Hi from Key Binding");
         }
      });

      JButton fooButton = new JButton("Foo");
      contentPane.setLayout(new FlowLayout());
      contentPane.add(fooButton);

      ablak.setVisible(true);
   }
}

然后按下按钮后会发生什么？告诉我哪个密钥处理例程有效？