Channel 9 Forums - Tech Off - Writing a managed version of ICreateDevEnum

Tech Off - Writing a managed version of ICreateDevEnum

cosminb — Sat, 11 Mar 2006 20:10:24 GMT

I have the following interface from "strmif.h" (DirectShow stuff):

    MIDL_INTERFACE("29840822-5B84-11D0-BD3B-00A0C911CE86")
    ICreateDevEnum : public IUnknown
    {
    public:
        virtual HRESULT STDMETHODCALLTYPE CreateClassEnumerator(
            /* [in] */ REFCLSID clsidDeviceClass,
            /* [out] */ IEnumMoniker **ppEnumMoniker,
            /* [in] */ DWORD dwFlags) = 0;

    };

I have found it described in C# like this (in a project called DShow.NET):

    [ComVisible(true), ComImport,
    Guid("29840822-5B84-11D0-BD3B-00A0C911CE86"),
    InterfaceType( ComInterfaceType.InterfaceIsIUnknown )]
public interface ICreateDevEnum
{
        [PreserveSig]
    int CreateClassEnumerator(
        [In]                                            ref Guid            pType,
        [Out]                                        out UCOMIEnumMoniker    ppEnumMoniker,
        [In]                                            int                    dwFlags );
}

The generated MSIL for the function is:

.method public hidebysig newslot abstract virtual
        instance int32 CreateClassEnumerator([in] valuetype [mscorlib]System.Guid& pType,
                                              [out] class [mscorlib]System.Runtime.InteropServices.UCOMIEnumMoniker& ppEnumMoniker,
                                              [in] int32 dwFlags) cil managed preservesig
{
} // end of method ICreateDevEnum::CreateClassEnumerator

And now my question is: How to represent this interface in C++/CLI? I use VS2005, and tried several times, but it doesn't compile. I am stuck on the IEnumMoniker parameter, don't know how to declare it.

Does anyone have an idea on how to write this interface in C++/CLI, so that I am able to cast the COM server 'SystemDeviceEnum' to the interface 'ICreateDevEnum'?

Thanks,
Cosmin

Tech Off - Writing a managed version of ICreateDevEnum

cosminb — Sat, 11 Mar 2006 20:51:57 GMT

Actually the whole problem reduces to being able to pass an interface as a parameter to a function:

namespace InterfaceTest
{

    public interface class Intf
    {
        void Read();
    };

    public ref class Class1
    {
        void Something(Intf i)
        {
        }
    };

}

This yields on the function 'Something':

error C3149: 'InterfaceTest::Intf' : cannot use this type here without a top-level '^'

Thanks

Tech Off - Writing a managed version of ICreateDevEnum

Sven Groot — Sun, 12 Mar 2006 22:05:25 GMT

cosminb wrote:

namespace InterfaceTest
{

    public interface class Intf
    {
        void Read();
    };

    public ref class Class1
    {
        void Something(Intf i)
        {
        }
    };

}

The change is in red:

namespace InterfaceTest
{

    public interface class Intf
    {
        void Read();
    };

    public ref class Class1
    {
        void Something(Intf ^i)
        {
        }
    };

}

EDIT: Since the original interface takes a double pointer to the interface, you're probably going to need "void Something(Intf ^%i)" there to pass a tracking reference to the managed pointer.