procedure VisibleChanging; dynamic;
DYNAMIC void __fastcall VisibleChanging();
Provides the interface for a method that responds to changes in the control's visibility.
VisibleChanging is called before the value of a control's Visible property changes. As implemented in TControl, it does nothing. Override VisibleChanging to respond to changes in the control's visibility. For example, if a control should not change its visibility, override VisibleChanging to raise an exception when an attempt is made to alter the control's visibility.