A listener which is notified when the current page of a multi-page dialog is
changing. Use this listener to perform long-running work that should only be
executed once, when the page is in the process of changing, rather then
during validation of page controls.
See Also:PageChangingEvent since: 3.3
Handle the an IDialogPage changing.
The doit field of the PageChangingEvent
must be set to false to prevent the page from changing.
Parameters: event - event object describing the change