Java - updating textFields from JList

Question

I am making an address book GUI with Java and I have a JList that displays all the names of the people in my ArrayList (this is populated by the updateinfo method mentioned below). I want it so when I click an item on the JList, the TextFields are then updated with that persons details. Before I have only used buttons and therefore actionListeners. I think I understand that a JList must use ListSelectionListener but I cannot seem to implement this. I have added a snippet of my code below. Can somebody please help?? For continuity with my actionlisteners I would like to have it as an inner class but this is not vital

JList jl;
DefaultListModel list;

list = new DefaultListModel();
this.jl = new JList(this.list);
//add ListSelectionListener????
updateList();
this.add(this.jl, layout);

Answer 1

You just add the selection listener to the list, like that:

jl.addSelectionListener(new ListSelectionListener() {

  public void valueChanged(ListSelectionEvent e) {
     // evaluate e if necessary and call a method
     // in your class to write the text in the textfield
     int selectedRow = e.getFirstIndex(); // more complicate for multiselects
     updateTextFieldWithName(selectedRow); // to be implemented
  }
});

Using an anonymous class like here is the quickest way. It's a bit hard to read but a typical pattern.

(just read you preferred an inner class, but I can't code that here on the fly with no IDE at hand...)

Answer 2

Yes you will want to use a ListSelectionListener for this, you will also probably want to set the list to single selection(ListSelectionModel.SINGLE_SELECTION). This will allow the user to only select one item in the list. You can then add you listSelectionListener, and in the valueChanged of the event do something like the following(not exact syntax).

valueChanged(ListSelectionEvent e){
   int idx = e.getFirstIndex();
   int idx2 = e.getLastIndex();  //idx and idx2 should be the same if you set SingleSel
   if(idx==idx2){
     //here you can get the person detail however you have them stored.  You can get   them from the model like so,
      Object personObj = MYLIST.getModel().getElementAt(int index); 
   }


 }

Answer 3

You can add the listener and then just query the currently selected index.

I did a sample for you, I hope you find it useful.

This is the relevant section:

    private JComponent list() {
        final JList list =  new JList( data);
        list.addListSelectionListener(new ListSelectionListener() {
          public void valueChanged(ListSelectionEvent e) {
            int i = list.getSelectedIndex();
            nameTextField.setText( i >= 0 ? data.get( i ) : "" );
          }
        });
        return new JScrollPane( list );
    }

Bear in mind that's not the only way to go, this is just an starting point for you.

Here's the complete working sample:

import java.util.Vector;
import java.util.Arrays;

import java.awt.BorderLayout;

import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JLabel;
import javax.swing.JComponent;

import javax.swing.event.ListSelectionListener;
import javax.swing.event.ListSelectionEvent;

public class JListSample {

    private Vector<String> data = new Vector<String>( 
            Arrays.asList( new String []  {
                    "one", "two", "three"  
            })
    );

    private JTextField nameTextField;

    public static void main( String [] args) {
        JListSample s = new JListSample();
        s.run();
    }
    public  void run() {
        JFrame frame = new JFrame("Selection test");
        frame.add( list(), BorderLayout.WEST );
        frame.add( editPanel() );
        frame.pack();
        frame.setVisible( true );

    }

    private JComponent list() {
        final JList list =  new JList( data);
        list.addListSelectionListener(new ListSelectionListener() {
          public void valueChanged(ListSelectionEvent e) {
            int i = list.getSelectedIndex();
            nameTextField.setText( i >= 0 ? data.get( i ) : "" );
          }
        });
        return new JScrollPane( list );
    }
    private JComponent editPanel() {
        JPanel panel = new JPanel();
        panel.add(  new JLabel("Name:") );
        nameTextField = new JTextField(10);
        panel.add( nameTextField );
        return panel;
    }
}

This is what is displayed:

Answer 4

I think I understand that a JList must use ListSelectionListener but I cannot seem to implement this

Well, then start by reading the JList API. You will find a link to the Swing tutorial on "How to Use Lists", which contains a working example.

Also in the tutorial you will find a section on "How to Write a List Selection Listener" which contains a second example.

Start with the tutorial for your basic questions.