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

Looking at the Example "ListSelectionModel: Enabling Toggle Selection Mode" here: http://java.sun.com/products/jfc/tsc/tech_topics/jlist_1/jlist.html

I have modified it slightly for multi-select list boxes (changed setSelectionInterval to addSelectionInterval) and eliminated a problem with re-selection if you click to de-select and move your mouse while the mouse is down (moved the gestureStarted check for both add and remove).

objList.setSelectionModel(new DefaultListSelectionModel() {
    private static final long serialVersionUID = 1L;

    boolean gestureStarted = false;

    @Override
    public void setSelectionInterval(int index0, int index1) {
        if(!gestureStarted){
            if (isSelectedIndex(index0)) {
                super.removeSelectionInterval(index0, index1);
            } else {
                super.addSelectionInterval(index0, index1);
            }
        }
        gestureStarted = true;
    }

    @Override
    public void setValueIsAdjusting(boolean isAdjusting) {
        if (isAdjusting == false) {
            gestureStarted = false;
        }
    }

});

Answer 2

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.

Answer 3

I know that this question already has an accepted answer, but I thought that I'd expand a bit, since I ended up stuck on this task for a few hours.

I was trying to implement a click-to-deselect action for selected items, but my list implementation requires the use of Single-Selection mode, specified by

JList jlist = new JList(new DefaultListModel());
jlist.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

Unfortunately, this led to exceptions and redundant calls for many of the solutions for the click-to-deselect problem on many SO questions, including this answer by FuryComptuers above. Due to code in DefaultListSelectionModel.class , specifically in the addSelectionInterval(int index0, int index1) and removeSelectionInterval(int index0, int index1) methods, which calls back to the setSelectionInterval(int index0, int index1) method, caused a circular call that leads to (obviously) exceptions. This "problem" code can be seen below.

 // If we only allow a single selection, channel through
    // setSelectionInterval() to enforce the rule.
    if (getSelectionMode() == SINGLE_SELECTION) {
        setSelectionInterval(index0, index1);
        return;
    }

Sawas Dalkitsis ' answer solved this problem, but would still act weird when dragging the mouse on a selected item (the selected item will select and de-select itself over and over while dragging the mouse). This wouldn't seem like a problem, but (apparently) I have a shaky hand, and minor mouse movements while clicked resulted in unwanted behavior. I combined Sawas Dalkitsis answer and FuryComptuers 's answer to get the following code, which seems to work as desired:

    JList jlist = new JList(new DefaultListModel());
    jList.setSelectionModel(new DefaultListSelectionModel() {
        private static final long serialVersionUID = 1L;

        boolean gestureStarted = false;

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

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

        @Override
        public void setValueIsAdjusting(boolean isAdjusting) {
            if (isAdjusting == false) {
                gestureStarted = false;
            }
        }

    });
    jList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

Note: I didn't check this against the ListSelectionModel.SINGLE_INTERVAL_SELECTION , as Sawas Dalkitsis did, so use caution if implementing it in that case.

Answer 4

I extended FuryComptuers answer to support multiple selection, and fixed an issue where setSelectionInterval didn't work if it was called directly.

public class ToggleableListSelectionModel extends DefaultListSelectionModel {
    private static final long serialVersionUID = 1L;

    private boolean mGestureStarted;

    @Override
    public void setSelectionInterval(int index0, int index1) {
        // Toggle only one element while the user is dragging the mouse
        if (!mGestureStarted) {
            if (isSelectedIndex(index0)) {
                super.removeSelectionInterval(index0, index1);
            } else {
                if (getSelectionMode() == SINGLE_SELECTION) {
                    super.setSelectionInterval(index0, index1);
                } else {
                    super.addSelectionInterval(index0, index1);
                }
            }
        }

        // Disable toggling till the adjusting is over, or keep it
        // enabled in case setSelectionInterval was called directly.
        mGestureStarted = getValueIsAdjusting();
    }

    @Override
    public void setValueIsAdjusting(boolean isAdjusting) {
        super.setValueIsAdjusting(isAdjusting);

        if (isAdjusting == false) {
            // Enable toggling
            mGestureStarted = false;
        }
    }   
}

Answer 5

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 6

Nick Dandoulakis' answer didn't quite work for me when selecting multiple items at once using a mouse click while pressing Shift .

The following ListSelectionModel behaves as I'd expect it when selecting items using mouseclicks with Shift or Ctrl .

Also, holding down Shift + Ctrl and pressing either → or ← selects items the way I want it to.

public static class ToggleableListSelectionModel extends DefaultListSelectionModel {
        private static final long serialVersionUID = 1L;

        @Override
        public void setSelectionInterval(int startIndex, int endIndex) {
            if (startIndex == endIndex) {
                if (multipleItemsAreCurrentlySelected()) {
                    clearSelection();
                }
                if (isSelectedIndex(startIndex)) {
                    clearSelection();
                }
                else {
                    super.setSelectionInterval(startIndex, endIndex);
                }
            }
            // User selected multiple items
            else {
                super.setSelectionInterval(startIndex, endIndex);
            }
        }

        private boolean multipleItemsCurrentlyAreSelected() {
            return getMinSelectionIndex() != getMaxSelectionIndex();
        }
    }