在Swing中向模型添加元素后，JList不会更新

Question

I'm having troubles updating a JList widget in Swing.

I'm creating a model, adding elements to it, then setting it as model for a JList element. Everything works well, it's showed correctly.

The problem is when I want to add an element to the model. It doesn't do anything.

I'm adding elements on the fly after an update from an Observer Pattern is fired.

What am I doing wrong ?

Here is the code of the UI.

// all the imports

    public class View extends JPanel implements Observer{
        private vivo vivox;
        private Label label = new Label("Hola Mundo");
        private DefaultListModel modelo = new DefaultListModel();
        private JList nameList = new JList(modelo);


        public View() {
            super();
            nameList.setFont(new Font("Arial",Font.BOLD,40));
            this.setLayout(new GridLayout());
            JButton button = new JButton("New Time");
            JButton button1 = new JButton("New Time2");
            label.setFont(new Font("Serif", Font.PLAIN, 50));
            JPanel group = new JPanel( new GridLayout());
            group.add(button);
            group.add(button1);

            JPanel east = new JPanel( new BorderLayout() );
            east.add(label, BorderLayout.NORTH);
            east.add(nameList, BorderLayout.CENTER);
            east.add(group, BorderLayout.SOUTH);

            add(east, BorderLayout.EAST);
            vivox = new vivo();
            vivox.addObserver(this);
            this.setListElements();
        }

        public void setListElements() {
            this.modelo.addElement("Messi");
            this.modelo.addElement("CR7");
            this.modelo.addElement("Iniesta");
        }

        @Override
        public void update(Observable o, Object arg) {
            this.label.setText("Some changes");
            this.modelo.addElement("Maradona");
        }


    }

Answer 1

The problem must be either with layout (that you dont see the actual happening changes) or is somewhere else as this shoult work. Here is working example that can show you, when adding new elements to list may be not visible (due to element size restrictions or actual size).

public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setLayout(new FlowLayout());
    DefaultListModel<String> model = new DefaultListModel<>();
    for (int i = 0; i < 5; i++) {
        model.addElement(String.valueOf(Math.random()));
    }
    JList list = new JList(model);
    JButton button = new JButton("Click me!");
    button.addActionListener(e -> model.addElement(String.valueOf(Math.random())));

    frame.add(list);
    frame.add(button);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400,200);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
} 

This is as simple as that. Notice that when you add couple elements you wont see the changes because they exceeds the frame, and you have to resize it. I think that similar issue may be in your case, or update code is not invoked at all.

PS: This is Java 8 example (used lambda - use anonymous ActionListener extending class in version<8 environements)