This event occurs when the selection in a Tree View control is about to change. EVENT-DATA-1 contains the reason for the change (see the Help file MSG-TV-SELCHANGE), and EVENT-DATA-2 contains the ID of the item that is about to be selected. You can prevent the selection from occurring by setting EVENT-ACTION to EVENT-ACTION-FAIL.
This event is generated much more often and in many more circumstances than may be anticipated. For example, the event is generated when the control goes active, even if the selection does not change. If the program is deployed with the thin client, the volume of these events can cause performance problems. The configuration variable TC_TV_SELCHANGING provides some control over the generation of these events in a thin client deployment. See the entry for TC_TV_SELCHANGING for more information.