Fundamentals of ATL COM Objects

The following illustration depicts the relationship among the various classes and interfaces used in defining an ATL COM object.

ATL Structure

ATL implements IUnknown in two phases:

• CComObject, CComAggObject, or CComPolyObject implements the IUnknown methods.
  
  
• CComObjectRoot or CComObjectRootEx manages the reference count and outer pointers of IUnknown.

Other aspects of your ATL COM object are handled by other classes:

• CComCoClass defines the object's default class factory and aggregation model.
  
  
• IDispatchImpl provides a default implementation of the IDispatch portion of any dual interfaces on the object.

For more information, see the following sections in this article:

• Implementing CComObjectRootEx
  
  
• Implementing CComObject, CComAggObject, and CComPolyObject
  
  
• Supporting IDispatch and IErrorInfo
  
  
• Supporting IDispEventImpl
  
  
• Changing the Default Class Factory and Aggregation Model
  
  
• Creating an Aggregate

For information about creating an ATL COM object, see the article Creating an ATL Project.