The trigger that represents the action taken when a view becomes visible, either as a result of being inserted into the visible view hierarchy or the view is no longer set as hidden.
Available in Mac OS X v10.5 and later.
Declaration Syntax Version Information- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)