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POInterop COM(-isch) interface marshaling results in AccessViotlationException on simple call
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copied!<p>I am trying to write a managed interop library for a native C++ plugin standard. This native C++ library uses a COM-compatible interface design. It does NOT however, do any of the class registration stuff. As with COM, all interfaces derive from IUnknown (called FUnknown but same 3 methods anyway).</p> <p>I have written a simple C++ console app that loads my managed test plugin and retrieves the initial (root) interface (an object factory pattern - much like com) through an exported method. I use a 3rd party DllExport code attribute implementation - that does seem to work fine. The C++ test app uses LoadLibrary/GetProcAddress and successfully retrieves a reference to the interface. I can set a breakpoint in my managed exported function and it gets hit as expected.</p> <p>Then the C++ test app calls AddRef on the IUnknown (part of the) interface and it returns 2 - as could be expected. Note that my managed interface definition (counter-part) does NOT derive from IUnknown -or include these methods. I would say that means that the managed marshaling magic has stepped in and provided a CCW.</p> <p>Then the C++ test app calls a simple method on the factory interface - one that just returns an int32 - and that also arrives in the managed implementation (breakpoint gets hit), but as that method returns it throws an AccessViolationException - somewhere in the managed-unmanaged transition.</p> <pre><code>class IPluginFactory : public FUnknown { public: // removed other methods before and after this one virtual int32 PLUGIN_API countClasses () = 0; }; </code></pre> <p>The int32 is a #define and the PLUGIN_API gets defined as __stdcall - which is COM compatible as far as I can tell.</p> <p>The managed representation of that interface I have defined as follows:</p> <pre><code>[ComImport] [Guid("same guid as in C++ file")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IPluginFactory { [return: MarshalAs(UnmanagedType.I4)] Int32 CountClasses(); } </code></pre> <p>The managed implementation of this method just returns a hard coded number (1).</p> <p>I have tried many things (so many I can not even remember them all) and am currently at a loss as how to resolve this, or what the problem could be.</p> <p>Any help is much appreciated. Thanx!</p> <p>EDIT: Request for details on FUnknown:</p> <pre><code>class FUnknown { public: virtual tresult PLUGIN_API queryInterface (const TUID iid, void** obj) = 0; virtual uint32 PLUGIN_API addRef () = 0; virtual uint32 PLUGIN_API release () = 0; }; </code></pre>

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