如何使用 Map 元素作为 JComboBox 的文本 [英] How to use Map element as text of a JComboBox

问题描述

我正在用集合的所有元素填充一个 JComboBox(使用 addItem()).集合中的每个元素都是一个 HashMap(所以它是一个 Hashmaps 的 ComboBox..).

I am populating a JComboBox (using addItem()) with all the elements of a collection. Each element in the collection is a HashMap (so its a ComboBox of Hashmaps..).

我的问题是 - 鉴于我需要每个项目都是 HashMap 我如何将文本设置为出现在 GUI 的组合框中?它需要是映射中某个键的值.通常，如果我用自己的类型填充组合框，我会覆盖 toString() 方法......但我不确定如何实现这一点，因为我使用的是 Java HashMap.

My question is - Given that I need each item to be a HashMap how do I set the text to apear in the combobox on the GUI? It needs to be the value of a certain key in the map. Normally if I am populating a combobox with my own type, I would just overide the toString() method...but I am not sure how to acheive this since I am using a Java HashMap.

有什么想法(如果可能，不实现我自己的 HashMap)?

Any ideas (if possible, without implementing my own HashMap)?

更新:如果我想要自定义功能，似乎没有办法避免让 JComboBox 覆盖 toString() 中的对象.我希望有一种方法来 (1) 指定要加载到 JComboBox 中的对象和 (2) 指定这些对象在 GUI 中的显示方式.

Update: It seems like there isn't anyway to avoid having the object int the JComboBox overide toString() if I want custom functionality..I wish there was a way to (1) specify the objects to be loaded into the JComboBox and (2) specify how these objects are to appear in the GUI.

推荐答案

(2) 指定这些对象如何出现在 GUI 中.

(2) specify how these objects are to appear in the GUI.

您可以将任何对象添加到模型中，然后创建自定义渲染器以您想要的任何方式显示对象.显示 toString() 方法和自定义渲染器方法的简单示例:

You can add any Object to the model and then create a custom renderer to display the object any way you want. Simple example that shows the toString() approach and custom renderer approach:

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

public class ComboBoxItem extends JFrame implements ActionListener
{
    public ComboBoxItem()
    {
        Vector model = new Vector();
        model.addElement( new Item(1, "car" ) );
        model.addElement( new Item(2, "plane" ) );
        model.addElement( new Item(3, "train" ) );
        model.addElement( new Item(4, "boat" ) );

        JComboBox comboBox;

        //  Easiest approach is to just override toString() method
        //  of the Item class

        comboBox = new JComboBox( model );
        comboBox.setDragEnabled(true);
        comboBox.addActionListener( this );
        getContentPane().add(comboBox, BorderLayout.NORTH );

        //  Most flexible approach is to create a custom render
        //  to diplay the Item data

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

    public void actionPerformed(ActionEvent e)
    {
        JComboBox comboBox = (JComboBox)e.getSource();
        Item item = (Item)comboBox.getSelectedItem();
        System.out.println( item.getId() + " : " + item.getDescription() );
    }

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

            if (value != null)
            {
                Item item = (Item)value;
                setText( item.getDescription().toUpperCase() );
            }

            if (index == -1)
            {
                Item item = (Item)value;
                setText( "" + item.getId() );
            }


            return this;
        }
    }

    class Item
    {
        private int id;
        private String description;

        public Item(int id, String description)
        {
            this.id = id;
            this.description = description;
        }

        public int getId()
        {
            return id;
        }

        public String getDescription()
        {
            return description;
        }

        public String toString()
        {
            return description;
        }
    }

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

}

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