ATL Event Handling Summary

In general, handling COM events is a relatively simple process. There are three main steps:

Implementing the Interface

There are four main ways of implementing an interface using ATL:

Derive from	Suitable for Interface type	Requires you to implement all methods*	Requires a type library at run time
The interface	Vtable	Yes	No
IDispatchImpl	Dual	Yes	Yes
IDispEventImpl	Dispinterface	No	Yes
IDispEventSimpleImpl	Dispinterface	No	No

* When using ATL support classes, you are never required to implement the IUnknown or IDispatch methods manually.

There are three main ways of advising and unadvising an event source using ATL.

Advise function	Unadvise function	Most suitable for use with	Requires you to keep track of a cookie?	Comments
AtlAdvise, CComPtr::Advise, or CComQIPtr::Advise	AtlUnadvise	Vtable or dual interfaces	Yes	AtlAdvise is a global ATL function; CComPtr::Advise and CComQIPtr::Advise just wrap calls to this function when the contained pointer is to an interface on the event source object.
IDispEventSimpleImpl: :DispEventAdvise	IDispEventSimpleImpl: :DispEventUnadvise	IDispEventImpl or IDispEventSimpleImpl	No	Fewer parameters than AtlAdvise since the base class does more work.
CComCompositeControl: :AdviseSinkMap	CComCompositeControl: :AdviseSinkMap	Composite controls derived from IDispEventImpl	No	CComCompositeControl::AdviseSinkMap advises all the entries in the event sink map. The same function unadvises the entries. This method is called automatically by the CComCompositeControl class.