ON_EVENT
Visual Studio 2010
Use the ON_EVENT macro to define an event handler function for an event fired by an OLE control.
ON_EVENT(theClass, id, dispid, pfnHandler, vtsParams )
The vtsParams argument is a space-separated list of values from the VTS_ constants. One or more of these values separated by spaces (not commas) specifies the function's parameter list. For example:
specifies a list containing a short integer followed by a BOOL.
For a list of the VTS_ constants, see EVENT_CUSTOM.