Arguments: dialog-item
Returns the value of the on-change event property of dialog-item. The value of the on-change property should be a function (function object or function name, such as a symbol) to be called when the dialog-item's value is changed. The application supplies this function to implement any side effects that should be done when the value changes. The on-change function will be called regardless of whether the value was changed interactively (by the user clicking on or typing into the component) or programmatically (via a call to (setf value)).
The value of on-change may be nil if no function needs to be called.
The function should take three arguments, which are (1) the control
(i.e. dialog-item), (2) the new value of
the control, and (3) the old (previous) value of the control.
The function should return true if the
application accepts the new value. If it returns nil, then the previous value will automatically be
restored to the control.
The on-change
function will only be called if the new value is different from the
old value. The value of the on-change-test event property is a
functions which takes the old and new values as arguments and returns
nil if they are different (and the
on-change
function should be called) and true if they are the same (and
on-change should not be called).
on-change is distinct from on-click. For example, if the user clicks an item-list control on the value that is already selected, then the on-click function will be called but not the on-change function (assuming that the on-change-test function returns true, which it will if it has the default value eql). On the other hand, if the value of a control is changed programmatically by application code, then the on-change function will be called but not the on-click function.
Common Graphics and IDE documentation is described in About Common Graphics and IDE documentation in cgide.htm. See also About event handling in the IDE in that document.
The documentation is described in introduction.htm and the index is in index.htm.
Copyright (c) 1998-2000, Franz Inc. Berkeley, CA., USA. All rights reserved.
Created 2000.10.5.