Question

I’m having a heck of a time understanding C++/CLI syntax. I have a member variable defined as so:

gcroot<Object^> m_DotNetContextFactory;

I’d like to cast this object to an IContextFactory interface.

If I were in C#, I would simply do the following:

object contextFactory = ...;
IContextFactory contextFactory = (IContextFactory)contextFactory;

Any ideas?

Answer 1

A double cast is required since you rooted Object^. I assume that’s the problem here. For example:

#include "stdafx.h"
#include <msclr\gcroot.h>
using namespace msclr;
using namespace System;

class native {
public:
    gcroot<Object^> m_foo;
};

interface class IBar {};
ref class managed : IBar {};


int main(array<System::String ^> ^args)
{
    native* nobj = new native;
    managed^ mobj = gcnew managed;
    nobj->m_foo = mobj;
    IBar^ itf = (IBar^)(Object^)nobj->m_foo;
    return 0;
}

Or make it a bit more readable with a helper variable:

    Object^ foo = nobj->m_foo;
    IBar^ itf = (IBar^)foo;