仅在选择项目时如何从JList获取项目

Question

In my program - a JApplet - I have a JList that is populated with a DefaultListModel . The user has the choice to select up to a certain number of items and indicate by pressing a JButton that he has finished his / her selection. I then use the items selected in the ActionPerformed event handler for the JButton .

This works great unless no item is selected before the JButton is pressed - if nothing is selected the rest of the instructions in my ActionPerformed don't operate either. I have tried myJList.isSelectionEmpty() as an negative if condition and also compared the array length I get from myJList.getSelectedIndices() to 0 but neither work.

However, if something is initially clicked and then deselected (I have a clear selection button), it works and in every subsequent time through the program it works, so it seems to be just the first time that it needs to be triggered.

Can anyone point me in the right direction?

Answer 1

If I understood you well, this might be one solution.

Initially, disable JButton. Then, provide your JList with ListSelectionListener; inside this event handler, check if the selection is made (at least one item selected). If it is - enable JButton; otherwise disable it. This way you will prevent execution of ActionEvent handler of JButton if no item is selected, which is what you want (I suppose). Suppose your JList is lstChoices, and your JButton is btnSubmit. This should do the above mentioned:

lstChoices.addListSelectionListener(new ListSelectionListener() {
        @Override
        public void valueChanged(ListSelectionEvent e)
        {
            if(lstChoices.getSelectedValuesList().size() > 0)
            {
                btnSubmit.setEnabled(true);
            }
            else
            {
                btnSubmit.setEnabled(false);
            }
        }
    });