Java Swing，JComboBox 下拉列表在单击前更改侦听器

Question

我有一个 JComboBox，它有一个 MIDI 文件列表，我想知道以下是否可行：当我点击 JComboBox 时，会打开一个下拉列表，当我将鼠标移到一个 MIDI 文件时，它会播放 10 秒示例声音，所以我在单击并选择该文件之前就知道文件包含什么，所以如果我有 50 个 midi 文件，我可以打开列表并在列表中上下移动鼠标而不点击它，但仍然播放 10鼠标指向的文件中的第二个样本，然后在我决定哪个样本后，单击它，该样本将成为 JComboBox 中的选定样本。

如何从 JComboBox 获得鼠标位置变化/指向事件的通知？

Answer 1

How to get notified for the mouse position change/pointing events 
from the JComboBox ?

• 通过实现ItemListener，触发两次（SELECTED和DESELECTED）

或者

• 在那里添加 CustomRenderer

或者 ...

例如 JComboBox 的三个可能的事件

import java.awt.Component;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.BasicComboBoxRenderer;


public class ComboBoxHoverOver {

    private JComboBox combo = new JComboBox();

    public ComboBoxHoverOver() {
        combo.setPrototypeDisplayValue("XXXXXXXXXXXXXXXXXXXXXX");
        combo.setRenderer(new ComboToolTipRenderer(combo));
        combo.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                System.out.println(combo.getSelectedItem().toString());
            }
        });
        combo.addItem("");
        combo.addItem("Long text 4");
        combo.addItem("Long text 3");
        combo.addItem("Long text 2");
        combo.addItem("Long text 1");
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(combo);
        f.pack();
        f.setVisible(true);
    }

    private class ComboToolTipRenderer extends BasicComboBoxRenderer {

        private static final long serialVersionUID = 1L;
        private JComboBox combo;
        private JList comboList;

        ComboToolTipRenderer(JComboBox combo) {
            this.combo = combo;
        }

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);
            if (comboList == null) {
                comboList = list;
                KeyAdapter listener = new KeyAdapter() {

                    @Override
                    public void keyReleased(KeyEvent e) {
                        if (e.getKeyCode() == KeyEvent.VK_DOWN || e.getKeyCode() == KeyEvent.VK_UP) {
                            int x = 5;
                            int y = comboList.indexToLocation(comboList.getSelectedIndex()).y;
                            System.out.println(comboList.getSelectedIndex());
                        }
                    }
                };
                combo.addKeyListener(listener);
                combo.getEditor().getEditorComponent().addKeyListener(listener);
            }
            if (isSelected) {
                System.out.println(value.toString());
            }
            return this;
        }
    }

    public static void main(String[] args) {

        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ComboBoxHoverOver comboBoxHoverOver = new ComboBoxHoverOver();
            }
        });
    }
}