java - 在 JComboBox 中使用向上/向下箭头滚动时，它不应该更新显示所选项目的顶部图 block

Question

我希望我的组合框顶部磁贴仅在我们按下回车键时更新，而不是在使用向上/向下箭头滚动时更新..

目前，当我使用向上/向下箭头滚动时，当前突出显示的当前项目正在 JComboBox 的顶部磁贴中更新为所选项目。我需要避免这种情况。

这是我的代码。提前致谢!

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

public class SwingControlDemo {
    private JFrame mainFrame;
    private JLabel headerLabel;
    private JLabel statusLabel;
    private JPanel controlPanel;

    public SwingControlDemo() {
        prepareGUI();
    }

    public static void main(String[] args) {
        SwingControlDemo swingControlDemo = new SwingControlDemo();
        swingControlDemo.showComboboxDemo();
    }

    private void prepareGUI() {
        mainFrame = new JFrame("Java Swing Examples");
        mainFrame.setSize(400, 400);
        mainFrame.setLayout(new GridLayout(3, 1));
        mainFrame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent windowEvent) {
                System.exit(0);
            }
        });
        headerLabel = new JLabel("", JLabel.CENTER);
        statusLabel = new JLabel("", JLabel.CENTER);

        statusLabel.setSize(350, 100);

        controlPanel = new JPanel();
        controlPanel.setLayout(new FlowLayout());

        mainFrame.add(headerLabel);
        mainFrame.add(controlPanel);
        mainFrame.add(statusLabel);
        mainFrame.setVisible(true);
    }

    private void showComboboxDemo() {
        headerLabel.setText("Control in action: JComboBox");

        final DefaultComboBoxModel fruitsName = new DefaultComboBoxModel();

        fruitsName.addElement("Apple");
        fruitsName.addElement("Grapes");
        fruitsName.addElement("Mango");
        fruitsName.addElement("Peer");
        fruitsName.addElement("java");
        fruitsName.addElement("Mango");

        final JComboBox fruitCombo = new JComboBox(fruitsName);
        fruitCombo.setSelectedIndex(0);

        JScrollPane fruitListScrollPane = new JScrollPane(fruitCombo);

        JButton showButton = new JButton("Show");

        fruitCombo.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent arg0) {
                if (arg0.getModifiers() == ActionEvent.MOUSE_EVENT_MASK || arg0.getModifiers() == ActionEvent.KEY_EVENT_MASK || true) {
                    System.out.println("arg0" + "  " + arg0.getModifiers());
                }
            }
        });

        fruitCombo.addKeyListener(new KeyListener() {
            @Override
            public void keyTyped(KeyEvent arg0) {
                // TODO Auto-generated method stub
            }

            @Override
            public void keyReleased(KeyEvent arg0) {
                // TODO Auto-generated method stub
                if (arg0.getKeyCode() == KeyEvent.VK_ENTER) {
                    System.out.println("enter key pressed" + arg0.getKeyCode());
                }
            }

            @Override
            public void keyPressed(KeyEvent arg0) {
                // TODO Auto-generated method stub
            }
        });

        System.out.println(fruitCombo.getComponentListeners().toString());
        controlPanel.add(fruitListScrollPane);
        controlPanel.add(showButton);
        mainFrame.setVisible(true);
    }
}

Answer 1

您可以在组合框上设置一个属性，以防止在使用箭头键时触发事件:

comboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);

注意:您可能(也可能不需要)在使用上述属性时手动关闭弹出窗口:

/*
    This works on non editable combo boxes
*/
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;
import javax.swing.text.*;

public class ComboBoxAction extends JFrame implements ActionListener
{
    public ComboBoxAction()
    {
        JComboBox<String> comboBox = new JComboBox<String>();
        comboBox.addActionListener( this );

        comboBox.addItem( "Item 1" );
        comboBox.addItem( "Item 2" );
        comboBox.addItem( "Item 3" );
        comboBox.addItem( "Item 4" );

        //  This prevents action events from being fired when the
        //  up/down arrow keys are used on the dropdown menu

        comboBox.putClientProperty("JComboBox.isTableCellEditor", Boolean.TRUE);

        getContentPane().add( comboBox );
        getContentPane().add( new JTextField(), BorderLayout.SOUTH );
    }

    public void actionPerformed(ActionEvent e)
    {
        System.out.println( e.getModifiers() );

        JComboBox comboBox = (JComboBox)e.getSource();
        System.out.println( comboBox.getSelectedItem() );

        //  make sure popup is closed when 'isTableCellEditor' is used

//      comboBox.hidePopup();
    }

    public static void main(String[] args)
    {
        ComboBoxAction frame = new ComboBoxAction();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible( true );
     }
}