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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 Interface
INonDelegatingUnknownA 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:
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.
See Also
GetInterface, CUnknown, IUnknown Macro
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