java - 自定义 JComboBox 顶部标签

Question

希望是一个简单的问题。

来自 http://download.oracle.com/docs/cd/E17409_01/javase/tutorial/uiswing/components/combobox.html 上的示例在“提供自定义渲染器”部分，我可以制作一个 JComboBox，如

Picture 3 - Text 3
-------------------
Picture 1 - Text 1
Picture 2 - Text 2
Picture 3 - Text 3
Picture 4 - Text 4
Picture 5 - Text 5

其中Picture 3 - Text 3为当前选中项。

是否可以自定义标签？比如

Text 3
-------------------
Picture 1 - Text 1
Picture 2 - Text 2
Picture 3 - Text 3
Picture 4 - Text 4
Picture 5 - Text 5

组合框处于最小化状态时不显示图像。

我以前使用过 JButton/未修饰的弹出 JFrame 来模拟这个，但我想知道是否可以使用纯 JComboBox

谢谢

Answer 1

Is it possible to have a custom label? Such as...

是的。同一个渲染器用于渲染下拉列表和组合框中的选定项。当“渲染器索引”为-1 时，选择的值为渲染器，因此您可以根据需要自定义渲染。像这样的东西:

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;

public class ComboBoxItemIcon extends JFrame
{
    public ComboBoxItemIcon()
    {
        Vector model = new Vector();
        model.addElement( new Item(new ImageIcon("copy16.gif"), "copy" ) );
        model.addElement( new Item(new ImageIcon("add16.gif"), "add" ) );
        model.addElement( new Item(new ImageIcon("about16.gif"), "about" ) );

        JComboBox comboBox;

        comboBox = new JComboBox( model );
        comboBox.setRenderer( new ItemRenderer() );
        getContentPane().add(comboBox, BorderLayout.SOUTH );
    }

    class ItemRenderer extends BasicComboBoxRenderer
    {
        public Component getListCellRendererComponent(
            JList list, Object value, int index,
            boolean isSelected, boolean cellHasFocus)
        {
            super.getListCellRendererComponent(list, value, index,
                isSelected, cellHasFocus);

            Item item = (Item)value;

            if (index == -1)
            {
                setText( item.getText() );
                setIcon( null );
            }
            else
            {
                setText( item.getText() );
                setIcon( item.getIcon() );
            }

            return this;
        }
    }

    class Item
    {
        private Icon icon;
        private String text;

        public Item(Icon icon, String text)
        {
            this.icon = icon;
            this.text = text;
        }

        public Icon getIcon()
        {
            return icon;
        }

        public String getText()
        {
            return text;
        }
    }

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

}