如何在 KeyEventDispatcher 触发后释放 KeyEvents 事件？

Question

我正在尝试为 java 中的 JFrame 表单实现 KeyListener。到目前为止，我使用了 code suggested here

并得到了相当不错的结果，但是当事件触发时（当按下任何所需的键时），似乎我不仅按下了最后一个键，而且随着事件的继续，我得到 2 , 3, etc, keys 的值（可以通过显示的 JOptionPane.showMessageDialog() 的数量看到）。

如何将事件的评估限制为仅按下最后一个键？或者，我如何在每次事件触发时 "clear" 按键数组？

这是我的表单的完整代码：

import java.awt.event.*;
import javax.swing.KeyStroke;
import javax.swing.Action;
import javax.swing.JOptionPane;
import java.awt.KeyEventDispatcher;
import java.awt.KeyEventPostProcessor;
import java.awt.KeyboardFocusManager;


public class frmMain extends javax.swing.JFrame {
    char optionselected;
    String other;
    private class MyDispatcher implements KeyEventDispatcher {
        @Override
        public boolean dispatchKeyEvent(KeyEvent e) {
            if (e.getID() == KeyEvent.KEY_RELEASED) { optionselected = e.getKeyChar(); }
            other = String.valueOf(optionselected).toUpperCase();
            switch (other) {
                case "C": JOptionPane.showMessageDialog(null, "Option 1"); break;
                case "T": JOptionPane.showMessageDialog(null, "Option 2"); break;
                case "D": JOptionPane.showMessageDialog(null, "Option 3"); break;
                case "N": JOptionPane.showMessageDialog(null, "Option 4"); break;
                case "O": JOptionPane.showMessageDialog(null, "Option 5"); break;
                case "S": JOptionPane.showMessageDialog(null, "Option 6"); break;
                default: break;
            }
            return false;
        }
    }    
    /**
     * Creates new form frmMain
     */
    public frmMain() {
        initComponents();
        KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
        manager.addKeyEventDispatcher(new MyDispatcher());     
    }

    /**
     * This method is called from within the constructor to initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is always
     * regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jInternalFrame1 = new javax.swing.JInternalFrame();
        jDesktopPane1 = new javax.swing.JDesktopPane();
        mbarMenu = new javax.swing.JMenuBar();
        mnuConta = new javax.swing.JMenu();
        mnuTeso = new javax.swing.JMenu();
        mnuDiezmo = new javax.swing.JMenu();
        mnuNomi = new javax.swing.JMenu();
        mnuCole = new javax.swing.JMenu();
        mnuExit = new javax.swing.JMenu();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setMaximumSize(new java.awt.Dimension(800, 600));
        setMinimumSize(new java.awt.Dimension(800, 600));
        setPreferredSize(new java.awt.Dimension(800, 600));
        setResizable(false);

        jInternalFrame1.setMaximumSize(new java.awt.Dimension(1000, 607));
        jInternalFrame1.setMinimumSize(new java.awt.Dimension(1000, 607));
        jInternalFrame1.setPreferredSize(new java.awt.Dimension(1000, 607));
        jInternalFrame1.setVisible(true);

        mnuConta.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/books_noun_9566_cc.png"))); // NOI18N
        mnuConta.setText("[C] = Option 1");
        mnuConta.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mbarMenu.add(mnuConta);

        mnuTeso.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/money_noun_197480_cc.png"))); // NOI18N
        mnuTeso.setText("[T] = Option 2");
        mnuTeso.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mbarMenu.add(mnuTeso);

        mnuDiezmo.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/diezmador_noun_247665_cc.png"))); // NOI18N
        mnuDiezmo.setText("[D] = Option 3");
        mnuDiezmo.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mbarMenu.add(mnuDiezmo);

        mnuNomi.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/payroll_noun_233106_cc.png"))); // NOI18N
        mnuNomi.setText("[N] = Option 4");
        mnuNomi.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mbarMenu.add(mnuNomi);

        mnuCole.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/school_noun_147545_cc.png"))); // NOI18N
        mnuCole.setText("[O] = Option 5");
        mnuCole.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mbarMenu.add(mnuCole);

        mnuExit.setIcon(new javax.swing.ImageIcon(getClass().getResource("/icons/logout_noun_14841_cc.png"))); // NOI18N
        mnuExit.setText("[S] = Option 6");
        mnuExit.setFont(new java.awt.Font("Arial", 0, 12)); // NOI18N
        mnuExit.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                mnuExitMouseClicked(evt);
            }
        });
        mbarMenu.add(mnuExit);

        jInternalFrame1.setJMenuBar(mbarMenu);

        javax.swing.GroupLayout jInternalFrame1Layout = new javax.swing.GroupLayout(jInternalFrame1.getContentPane());
        jInternalFrame1.getContentPane().setLayout(jInternalFrame1Layout);
        jInternalFrame1Layout.setHorizontalGroup(
            jInternalFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jDesktopPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 989, Short.MAX_VALUE)
        );
        jInternalFrame1Layout.setVerticalGroup(
            jInternalFrame1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jDesktopPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 539, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jInternalFrame1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jInternalFrame1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        pack();
    }// </editor-fold>                        

    private void mnuExitMouseClicked(java.awt.event.MouseEvent evt) {                                     
        this.dispose();
        System.exit(0);
    }                                    

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(frmMain.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(frmMain.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(frmMain.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(frmMain.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new frmMain().setVisible(true);
            }
        });
    }

    public static void salida(){
        System.exit(0);
    }

    // Variables declaration - do not modify                     
    private javax.swing.JDesktopPane jDesktopPane1;
    private javax.swing.JInternalFrame jInternalFrame1;
    private javax.swing.JMenuBar mbarMenu;
    private javax.swing.JMenu mnuCole;
    private javax.swing.JMenu mnuConta;
    private javax.swing.JMenu mnuDiezmo;
    private javax.swing.JMenu mnuExit;
    private javax.swing.JMenu mnuNomi;
    private javax.swing.JMenu mnuTeso;
    // End of variables declaration                   
}

MyDispatcher class 实现了 KeyListener，并且应该在每次按下所需的键时仅引发一次 JOptionPane.showMessageDialog()。

提前感谢您提供有关该主题的任何指导。

Answer 1

来自the documentation for dispatchKeyEvent：

Return true if the KeyboardFocusManager should take no further action with regard to the KeyEvent; false otherwise

当不需要进一步处理事件时，您也可以在 dispatchKeyEvent 实现中直接使用事件。

e.consume();

@MadProgrammer 的建议也很重要。使用全局事件处理可能性是最后的选择。

Answer 2

基本问题是，您同时获得了按键事件和按键释放事件，但您仅在按键释放时更改了 optionselected。

所以：

按C，在keyPressed，optionSelected是null，other将是null，在 keyReleased 上，optionSelected 变为 C，显示对话框
按 T，在 keyPressed optionselected 上（仍然）C，显示对话框，在 keyReleased optionselected 变为 T，显示对话框

相反，您应该只处理 keyReleased 事件

private class MyDispatcher implements KeyEventDispatcher {

    @Override
    public boolean dispatchKeyEvent(KeyEvent e) {
        if (e.getID() == KeyEvent.KEY_RELEASED) {
            optionselected = e.getKeyChar();
            other = String.valueOf(optionselected).toUpperCase();
            switch (other) {
                case "C":
                    JOptionPane.showMessageDialog(null, "Option 1");
                    break;
                case "T":
                    JOptionPane.showMessageDialog(null, "Option 2");
                    break;
                case "D":
                    JOptionPane.showMessageDialog(null, "Option 3");
                    break;
                case "N":
                    JOptionPane.showMessageDialog(null, "Option 4");
                    break;
                case "O":
                    JOptionPane.showMessageDialog(null, "Option 5");
                    break;
                case "S":
                    JOptionPane.showMessageDialog(null, "Option 6");
                    break;
                default:
                    break;
            }
        }
        return false;
    }
}

话虽如此，KeyEventDispatcher 级别非常非常低，更好的解决方案可能是使用键绑定 API，请参阅 How to Use Key Bindings 了解更多详情

如何在 KeyEventDispatcher 触发后释放 KeyEvents 事件？

How to release KeyEvents events after KeyEventDispatcher fires?

java

swing

keylistener

jframe

keyboard-events