C++ – ATL simple object wizard – “Object Xxx already exists” error

atlccomvisual studiovisual-studio-2005

I am attempting to create a new COM object in my DLL using the ATL Simple Object Wizard in Visual Studio 2005.

I enter the short name for the object, and all of the other fields are derived.

However, when I click Next in the wizard, the following error message comes up:

Object 'IXxxInterfaceName' already exists

I have searched my entire solution for all references to IXxxInterfaceName and can't see it defined anywhere.

How is the wizard determining that it exists already?

Best Answer

I never found out why the wizard determined that the object name existed already - I'm guessing something was cached somewhere that I couldn't track down.

In the end, I appended a 2 to the end of the interface name when creating it which allowed it to be added. Then I replaced all the occurrences of IXxxInterfaceName2 with IXxxInterfaceName. Everything worked after this.

If I ever track down the root cause of this problem, I'll update the answer.

Related Solutions

C++ – How to make an ATL COM class derived from a base class

Just a suggestion - if your COM object does not need to do anything special with COM related stuff then you can implement code such that the real logic that your base COM class does is encapsulated in another plain old C++ class say CBaseLogic.

CBaseLogic : IBase

class ATL_NO_VTABLE CBase :
    public CComObjectRootEx<CComSingleThreadModel>,
    public CComCoClass<CBase, &CLSID_Base>,
    public ISupportErrorInfo,
    public IConnectionPointContainerImpl<CBase>,
    public CProxy_IBaseEvents<CBase>,
    public IDispatchImpl<IBase, &IID_IBase, &LIBID_ExampleLib
{
CBaseLogic m_LogicObj; /* Method calls are simply forwarded to this member */
};


CDerivedLogic : public CBaseLogic

class ATL_NO_VTABLE CDerived :
    public CComObjectRootEx<CComSingleThreadModel>,
    public CComCoClass<CDerived, &CLSID_Base>,
    public ISupportErrorInfo,
    public IConnectionPointContainerImpl<CDerived>,
    public CProxy_IBaseEvents<CDerived>,
    public IDispatchImpl<IBase, &IID_IBase, &LIBID_ExampleLib
{
CDerivedLogic m_LogicObj;
};

This achieves what you are trying to do with the added advantage of

Keeps your real program logic separate from the infrastructure / packaging (COM)
Makes the real logic platform independent.
Future maintainer need not understand your clever COM hack
Keeps your program logic clean and away from the COM syntax, improving readability
Makes re-use of real logic easier in other forms of packaging eg as a C DLL

C++ – How to work-around “Object required” error when adding a variable in an ATL Dialog

This may helps. This is while adding the class. Same thing may apply for adding variables.

Best Answer

Related Solutions

C++ – How to make an ATL COM class derived from a base class

C++ – How to work-around “Object required” error when adding a variable in an ATL Dialog

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