动态JComboBoxes

Question

I have following data (String):

Course1: A1
Course1: A2
Course2: B1
Course2: B2
Course2: B3
Course2: B4
Course3: C1
Course3: C2

I'd like to create two JComboBox (JComboBox1, JComboBox2) so that JComboBox1 contains Course1,Course2,Course3, etc.

If I select, say, Course2 from JComboBox1 then corresponding B1,B2,B3,B4 should be populated in JComboBox2.

How to implement this? Many Thanks.

Answer 1

Yes, simply create a DefaultComboBoxModel for each set, and do setModel() on JComboBox2 when JComboBox1 changes.

Addendum: For example,

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ComboBoxModel;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class ComboTest extends JPanel implements ActionListener, Runnable {

    private final JComboBox combo1 = new JComboBox(
        new String[]{"Course 1", "Course 2", "Course 3"});
    private final JComboBox combo2 = new JComboBox();
    private ComboBoxModel[] models = new ComboBoxModel[3];

    public ComboTest() {
        models[0] = new DefaultComboBoxModel(
            new String[]{"A1", "A2"});
        models[1] = new DefaultComboBoxModel(
            new String[]{"B1", "B2", "B3", "B4"});
        models[2] = new DefaultComboBoxModel(
            new String[]{"C1", "C2"});

        combo2.setModel(models[0]);
        this.add(combo1);
        this.add(combo2);
        combo1.addActionListener(this);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        int i = combo1.getSelectedIndex();
        combo2.setModel(models[i]);
    }

    @Override
    public void run() {
        JFrame f = new JFrame("ComboTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new ComboTest());
    }
}

Answer 2

Yes. You can add a change event listener to the first JComboBox that updates the values of the second JComboBox.

Something like this

// first comboBox
final JComboBox courseBox = new JComboBox(
                               new String[]{"Course 1", "Course 2", "Course 3"});

final JComboBox box2 = new JComboBox();

// Now listen for changes
courseBox.addActionListener(new ActionListener(){
   void actionPerformed(ActionEvent e){
       if(courseBox.getSelectedItem().equals("Course 1")){
           // we know that the user picked "Course 1", now change box2 to match
           // first clear everything
           box2.removeAllItems();
           // now add back relevant values
           box2.addItem("A1");
           box2.addItem("A2");
       }else if(...){
           // ...
       }
   }
});