JComboBox 在每个项目中都有不同的颜色失败

Question

• Purpose : to have a JComboBox with different background colors and text in each item.
• My problem : The background color doesn't change, and the text is not what I've set in setText, which have been correctly shown in System.out.println. The getSelectedIndex() works well.

The capture: http://i.stack.imgur.com/EgfZs.png

The following is the code after I've digested and try-and-error what Dr.Google shows:

public class ColorCode{
   private Color color;
   private String alias;
   ...
}
public class ElectronicColorCode extends JFrame implements ActionListener{
   private JComboBox[] selections = new JComboBox[4];
   ...
   public ElectronicColorCode(){
      for(int i=0; i<selections.length; i++){
         selections[i] = new JComboBox();
         for(int j=0; j<tolColorSets.length; j++)
            selections[i].addItem(new ComboBoxRenderer(colorSets[j]));
      }
      selections[i].addActionListener(this);
      ...
   }
}
class ComboBoxRenderer extends JLabel implements ListCellRenderer{
   private ColorCode colorCode;

   public ComboBoxRenderer(ColorCode colorCode){
      super();
      this.colorCode = colorCode;
      setBackground(colorCode.getColor());
      setText(colorCode.getAlias());
      System.out.println(colorCode.getAlias());
   }

   public Component getListCellRendererComponent(JList list, Object obj, int row, boolean isSelected, boolean hasFocus){
      return this;
   }
}

Answer 1

You don't add renderers as an item for the combo box. The renderer is used to renderer the Object that is stored in the model. If you want you can add a custom object to the model that contains both the text and the background color you want displayed in the renderer.

Here is a simple example that shows how to do this. You will obviously need to customize the code to store and render the background color instead of the id.

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

public class ComboBoxItem2 extends JFrame implements ActionListener
{
    public ComboBoxItem2()
    {
        Vector model = new Vector();
        model.addElement( new Item(1, "car" ) );
        model.addElement( new Item(2, "plane" ) );
        model.addElement( new Item(4, "boat" ) );
        model.addElement( new Item(3, "train" ) );

        JComboBox comboBox = new JComboBox( model );
        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);

            Item item = (Item)value;
            setText( item.getDescription().toUpperCase() );

            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 ComboBoxItem2();
        frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
        frame.pack();
        frame.setVisible( true );
     }

}