java - 按键监听器不工作

Question

public class KL implements KeyListener {

 public static void main(String[] args) {
        final JPopupMenu popup = new JPopupMenu();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 200);
        frame.setVisible(true);

    }

@Override
public void keyPressed(KeyEvent arg0) {
    System.out.println(arg0.getKeyChar());
}

@Override
public void keyReleased(KeyEvent e) {
    System.out.println(e.getKeyChar());

}

@Override
public void keyTyped(KeyEvent e) {
    System.out.println(e.getKeyChar());

}
}

那是我的类(class)，对我来说这可能是非常愚蠢的事情，但是我的 KeyListener 不起作用。控制台上没有任何显示。

Answer 1

让我们从您没有将监听器附加到任何东西的事实开始，然后继续讨论您确实应该使用 Key Bindings 的事实

举例

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class TestTableEditing {

    public static void main(String[] args) {
        new TestTableEditing();
    }

    public TestTableEditing() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JLabel key;
        private int counter = 0;

        public TestPane() {
            key = new JLabel("...");
            add(key);
            InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
            ActionMap am = getActionMap();
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0), "A.pressed");
            am.put("A.pressed", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    System.out.println("A was pressed");
                    key.setText("A was pressed " + (++counter));
                }
            });
        }

    }

}