INonDelegatingUnknown

[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The INonDelegatingUnknown interface is a version of IUnknown that is renamed to enable support for both nondelegating and delegating IUnknown interfaces in the same COM object.

Syntax

interface INonDelegatingUnknown
{
    virtual HRESULT NonDelegatingQueryInterface(REFIID riid, LPVOID *ppv) PURE;
    virtual ULONG NonDelegatingAddRef(void) PURE;
    virtual ULONG NonDelegatingRelease(void) PURE;
};

Remarks

To use INonDelegatingUnknown for multiple inheritance, perform the following steps.

1. Derive your class from an interface, for example, IMyInterface.

2. Include DECLARE_IUNKNOWN in your class definition to declare implementations of QueryInterface, AddRef, and Release that call the outer unknown.

3. 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);
        }
   

4. Declare and implement the member functions of IMyInterface.

To use INonDelegatingUnknown for nested interfaces, perform the following steps:

1. Declare a class derived from CUnknown.

2. Include DECLARE_IUNKNOWN in your class definition.

3. 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);
        }
   

4. Implement the member functions of IMyInterface. Use CUnknown::GetOwner to access the COM object class.

5. 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.

Requirements

See also

COM Helper Functions