JList - deselect when clicking an already selected item

Question

If a selected index on a JList is clicked, I want it to de-select. In other words, clicking on the indices actually toggles their selection. Didn't look like this was supported, so I tried

list.addMouseListener(new MouseAdapter()
{
   public void mousePressed(MouseEvent evt)
   {
      java.awt.Point point = evt.getPoint();
      int index = list.locationToIndex(point);
      if (list.isSelectedIndex(index))
         list.removeSelectionInterval(index, index);
   }
});

The problem here is that this is being invoked after JList has already acted on the mouse event, so it deselects everything. So then I tried removing all of JList's MouseListeners, adding my own, and then adding all of the default listeners back. That didn't work, since JList would reselect the index after I had deselected it. Anyway, what I eventually came up with is

MouseListener[] mls = list.getMouseListeners();
for (MouseListener ml : mls)
   list.removeMouseListener(ml);
list.addMouseListener(new MouseAdapter()
{
   public void mousePressed(MouseEvent evt)
   {
      java.awt.Point point = evt.getPoint();
      final int index = list.locationToIndex(point);
      if (list.isSelectedIndex(index))
         SwingUtilities.invokeLater(new Runnable()
         {
            public void run()
            {
               list.removeSelectionInterval(index, index);
            }
         });
   }
});
for (MouseListener ml : mls)
   list.addMouseListener(ml);

... and that works. But I don't like it. Is there a better way?

Answer 1

You could always the ListSelectionListener instead of deciphering the point clicked and then translating it to the item selected.

http://java.sun.com/docs/books/tutorial/uiswing/examples/events/index.html#ListSelectionDemo

http://java.sun.com/docs/books/tutorial/uiswing/events/listselectionlistener.html

http://java.sun.com/docs/books/tutorial/uiswing/examples/events/ListSelectionDemoProject/src/events/ListSelectionDemo.java

In the above link for java file there is an implementation which can be easily improved to do "deselection" :)

Answer 2

For an approach that uses a ListSelectionListener check out this posting

Answer 3

How about this?

import javax.swing.DefaultListSelectionModel;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.ListSelectionModel;

public class A {
    public static void main(String[] args) {
        JFrame f = new JFrame("Test");
        final JList list = new JList(new String[] {"one","two","three","four"});
        list.setSelectionModel(new DefaultListSelectionModel(){


            @Override
            public void setSelectionInterval(int index0, int index1) {
                if (index0==index1) {
                    if (isSelectedIndex(index0)) {
                        removeSelectionInterval(index0, index0);
                        return;
                    }
                }
                super.setSelectionInterval(index0, index1);
            }

            @Override
            public void addSelectionInterval(int index0, int index1) {
                if (index0==index1) {
                    if (isSelectedIndex(index0)) {
                        removeSelectionInterval(index0, index0);
                        return;
                    }
                super.addSelectionInterval(index0, index1);
                }
            }

        });
        f.getContentPane().add(list);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.pack();
        f.setVisible(true);
    }

}

It works but note one side effect... If you set the mode to multi selction like this for instance:

list.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION );

you cannot select multiple objects via mouse drag. Ctrl (or shift) click works. I'm sure it can be fixed but i assume you asked this for single selection lists... If not modify your question and we can start thinking for solutions to the multiple selection problem.