How to dynamically add items to a JList?

Question

I'm having trouble adding items to a JList called lstContacts whenever a button is pressed.

When I press my new contact button, a line should be added to lstContacts but when I press the button nothing happens.

Here is my action listener for the new contact button:

newContactButton.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            Contacts contacts = new Contacts();

            contacts.createContact();
        }
    });

Here is my createContact method in the contacts class:

ArrayList<String> contactsList = new ArrayList<String>();
public void createContact() {
    ContactsDB database = new ContactsDB();
    System.out.println("new contact");
    contactsList.add("New Contact");
    listModel.addElement("New Contact");
}

And lastly here is my createCustomUIComponent() method:

private void createUIComponents() {
    // TODO: place custom component creation code here
    listModel = new DefaultListModel();
    lstContacts = new JList<String>(listModel);
}

Why aren't the new contacts getting added to my JList?

Answer 1

The problem is here:

Contacts contacts = new Contacts();

contacts.createContact();

You are creating a new contacts object every time you click the button, but the JList doesn't have a reference to the Contacts object. I don't know how the contacts object is defined, but you should make sure that the object you are adding the contact to has reference to the DefaultListModel.

Another problem I see (but isn't causing the problem you posted about) is that you call new DefaultListModel(), but list model is a parameterized type. You probably want to call new DefaultListModel<String>().

Answer 2

1. Don't create an ArrayList of Contacts. All the Contact data should be stored in the ListModel.

2. So when you click on the button all you do is create a Contact and add the Contact to the DefaultListModel. However, your code doesn't make much sense because you're just creating an empty Contact. I would expect the Contact to have a name or something. So really what you want to do is have a text field were the user can enter a name and then when you click the button you create a Contact using the name data and then add the Contact to the list.

Read the section from the Swing tutorial on How to Use Lists. The ListDemo example show you how to dynamically add/remove an item from the DefaultListModel. Download the example and modify the working example to meet your specific requirements. When learning a new concept, start with working code.

Answer 3

First of all you have to have new a default ListView:

 DefaultListModel listModel = new DefaultListModel();

Thenm build your JList with this list:

 JList jList = new JList(listModel);

Anytime you want to change your list for each action you considered, call addElement on your jList:

listModel.addElement("This is a test contact");