Can't addElement to JList

Question

I know this isn't the only question about filling JLists, but I didn't find the answer in another SO thread.

I've used the Netbeans GUI builder to create my GUI. The JList is added to a scrollpane, if I hardcode the content of the JList everything is showed fine.

jList1.setModel(new javax.swing.AbstractListModel() { 
public String[] strings = {"1", "2", "etc..."}; 
@Override 
  public int getSize() { 
  return strings.length; 
} 

@Override 
   public Object getElementAt(int i) { 
   return strings[i]; 
} 
});

But if I try to add items dynamically via SwingWorker, nothing appears.

JList jList1 = new javax.swing.JList();
DefaultListModel info = new DefaultListModel();
....
jList1.setModel(info);

....
public void FillList(final String subject) {

    worker = new SwingWorker() {
        @Override
        protected Object doInBackground() {
            info.addElement(subject);

            return 0;
        }

        @Override
        protected void done() {
        }
    };
    worker.execute();
}

I just want to show the subjects in the JList for visual purposes, the rest is done in the background.

Any help is appreciated,

Thanks!

Are you sure the code is executing? A little debuggin or even a `System.out.println` well placed can give a lot of perspective. — SJuan76, Oct 05 '12 at 10:45
Thanks for your answer. Yes I am sure it is executing. If place this line: `System.out.println(info.getSize());` in `doInBackground()` the size of the `ListModel` increments. — Jef, Oct 05 '12 at 10:49
When you use dynamic content, are you storing the dynamic content in the array "strings"? — Clark, Oct 05 '12 at 10:54
Oops I forgot to change the `getSize()` and `getElementAt()` methods. But in another class I retrieve certain messages from an e-mail account, from which I take the subject and call `FillList(subject)` so FillList gets called for every e-mail. I just want to show the subjects in the JList for visual purposes, the rest is done in the background. — Jef, Oct 05 '12 at 11:01
**WRONG** - you _must not_ change a component (neither any of its properties nor the underlying model) from the worker thread, that is **NOT** in doInBackground() — kleopatra, Oct 05 '12 at 11:02

score 3 · Accepted Answer · edited May 23 '17 at 12:04

3

Swing is single threaded and all output to the visible GUI must be done on EDT
you have an issue with Concurency in Swing
output from SwingWorkers methods doInBackground() doesn't notified EventDispatchThread
then any changes in ListModel isn't visible in the Swing GUI
have to override publish() or process(), these two methods quite quarenteed that output will be doe on EDT

edited May 23 '17 at 12:04

Community

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answered Oct 05 '12 at 10:52

mKorbel

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Thanks for your answer! Going to put some time in reading those links, thanks for your help. – Jef Oct 05 '12 at 11:03

Can't addElement to JList

1 Answers1