Java 键绑定不起作用

Question

我正在尝试在 JPanel 上使用 Java 进行键绑定。当我按下“w”按钮时，我希望执行某个操作。我按照 Java 教程进行绑定，但 actionPerformed 方法没有执行（即没有文本打印出来）。以下是我的测试 GUI 的全部代码，相关部分突出显示：

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;

@SuppressWarnings("serial")
public class Test extends JFrame{

private JPanel panel;

public Test(){
    super();
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setSize(500,500);
    setLayout(new BorderLayout());
    setVisible(true);        
    panel = new JPanel();

    // HERE ARE THE KEY BINDINGS
    panel.getInputMap().put(KeyStroke.getKeyStroke('w'),"forward");
    panel.getActionMap().put("forward", new AbstractAction(){
        @Override
        public void actionPerformed(ActionEvent e){
            System.out.println("test");
        }
    });
    // END OF KEY BINDINGS

    add(panel, BorderLayout.CENTER);
}

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

}

永远不会打印文本“test”。我已经多次尝试使用许多不同的变体、不同的键，并且我确保面板处于焦点位置，但没有运气。我究竟做错了什么？

Answer 1

问题在于您查找KeyStroke 的方式。 KeyStroke.getKeyStroke('w') 将返回 typed w，由于某种原因，它不会触发关键事件。这就是为什么我倾向于避免这种方法。而是使用

panel.getInputMap().put(KeyStroke.getKeyStroke("W"),"forward");

或

panel.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0),"forward");

另外，您可能想要为InputMap 定义焦点约束，类似于

panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW)...

会更安全...但您需要确定希望从哪个级别触发击键

请参阅JComponent 和How to use Key Bindings 了解更多详情

更新示例

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.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test extends JFrame {

    private JPanel panel;

    public Test() {
        super();
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(500, 500);
        setLayout(new BorderLayout());
        setVisible(true);
        panel = new JPanel();

        // HERE ARE THE KEY BINDINGS
        panel.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0), "forward");
        panel.getActionMap().put("forward", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("test");
            }
        });
        // END OF KEY BINDINGS

        add(panel, BorderLayout.CENTER);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                new Test();
            }
        });
    }
}