As well as selecting items, users often want to deselect them. Items in multiple-selection and extended-selection lists may be deselected.
In a multiple-selection list, deselection is done by clicking on the selected item again with either of the selection or extension gestures.
In an extended-selection list, deselection is done by performing the extension gesture upon the selected item. (If this was done using the selection gesture, the list would behave as a single-selection list and all other selections would be lost.)
Just like a selection, a deselection -- or retraction -- can have a callback associated with it.
For a multiple-selection list pane, there may be the following callbacks:
:selection-callback -- called when a selection is made :retract-callback -- called when a selection is retracted Consider the following example. The function set-title changes the title of the interface to the value of the argument passed to it. By using this as the callback to the check-button-panel , the title of the interface is set to the current selection. The function retract-callback returns a message dialog with the name of the button retracted.
(defun set-title (data interface)
(setf (interface-title interface)
(format nil "~S" data)))
(make-instance 'check-button-panel
:items '(one two three four five)
:print-function 'string-capitalize
:selection-callback 'set-title
:retract-callback 'test-callback)
(contain *) 
Figure 4.5 An example of a callback to a check-button panel
For an extended-selection list pane, there may be the following callbacks:
:selection-callback -- called when a selection is made :retract-callback -- called when a selection is retracted :extend-callback -- called when a selection is extendedAlso available in extended-selection and single-selection lists is the action callback. This is called when you double-click on an item.