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, CComPtrBase::Advise	AtlUnadvise	Vtable or dual interfaces	Yes	`AtlAdvise` is a global ATL function. `CComPtrBase::Advise` is used by CComPtr and CComQIPtr.
IDispEventSimpleImpl::DispEventAdvise	IDispEventSimpleImpl::DispEventUnadvise	IDispEventImpl or IDispEventSimpleImpl	No	Fewer parameters than `AtlAdvise` since the base class does more work.
CComCompositeControl::AdviseSinkMap(TRUE)	CComCompositeControl::AdviseSinkMap(FALSE)	ActiveX controls in Composite controls	No	`CComCompositeControl::AdviseSinkMap` advises all entries in the event sink map. The same function unadvises the entries. This method is called automatically by the `CComCompositeControl` class.
CAxDialogImpl::AdviseSinkMap(TRUE)	CAxDialogImpl::AdviseSinkMap(FALSE)	ActiveX controls in a dialog box	No	`CAxDialogImpl::AdviseSinkMap` advises and unadvises all ActiveX controls in the dialog resource. This is done automatically for you.