INonDelegatingUnknown Interface

To enable a class to support both nondelegating and delegating IUnknown interfaces in the same COM object, the Combase.h header file declares the INonDelegatingUnknown interface. This interface is a version of IUnknown and has three methods:

INonDelegatingUnknown::NonDelegatingQueryInterface
INonDelegatingUnknown::NonDelegatingAddRef
INonDelegatingUnknown::NonDelegatingRelease

For sample implementations of these methods, see CUnknown::NonDelegatingQueryInterface, CUnknown::NonDelegatingAddRef, and CUnknown::NonDelegatingRelease.

INonDelegatingUnknown

A version of IUnknown renamed to enable a class to support both nondelegating and delegating IUnknown interfaces in the same COM object. The interface supports the following three methods, in vtable order.

Syntax

HRESULT NonDelegatingQueryInterface(

  REFIID iid,

  void **ppvObject );

ULONG NonDelegatingAddRef(void);

ULONG NonDelegatingRelease(void);

Remarks

To use INonDelegatingUnknown for multiple inheritance, perform the following steps.
Derive your class from an interface, for example, IMyInterface.
Include DECLARE_IUNKNOWN in your class definition to declare implementations of QueryInterface, AddRef, and Release that call the outer unknown.
Override NonDelegatingQueryInterface to expose IMyInterface with code such as the following:
     if (riid == IID_IMyInterface) {
         return GetInterface((IMyInterface *) this, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }
Declare and implement the member functions of IMyInterface.
To use INonDelegatingUnknown for nested interfaces, perform the following steps:
Declare a class derived from CUnknown.
Include DECLARE_IUNKNOWN in your class definition.
Override NonDelegatingQueryInterface to expose IMyInterface with the code such as the following:
     if (riid == IID_IMyInterface) {
         return GetInterface((IMyInterface *) this, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }
Implement the member functions of IMyInterface. Use CUnknown::GetOwner to access the COM object class.
In your COM object class, make the nested class a friend of the COM object class, and declare an instance of the nested class as a member of the COM object class.
Because you must always pass the outer unknown and an HRESULT to the CUnknown constructor, you can't use a default constructor. You have to make the member variable a pointer to the class and make a new call in your constructor to actually create it.
Override the NonDelegatingQueryInterface with code such as the following:
     if (riid == IID_IMyInterface) {
         return m_pImplFilter->
            NonDelegatingQueryInterface(IID_IMyInterface, ppv);
     } else {
         return CUnknown::NonDelegatingQueryInterface(riid, ppv);
     }
You can have mixed classes that support some interfaces through multiple inheritance and some interfaces through nested classes.