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POUsing C++ COM interface in C# for both client and server
 

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    <p>I need to make a piece of C# code interact through COM with all kinds of implementations.</p> <p>To make it easeier for users of that integration, I included the interacted interfaces in IDL (as part of a relevant existing DLL, but without coclass or implementation), then got that into my C# code by running Tlbimp to create the types definition.</p> <p>I implemented my C#, creating COM objects based on Windows registry info and casting the object into the interface I need.</p> <p>I then created a C# implementation of the interface in a seperate project and registered it. The main program creates the testing COM object correctly but fails to cast it into the interface (gets a null object when using C# 'as', gets an InvalidCastException of explicit cast).</p> <p>Can someone suggest why the interface is not identified as implemented by the testing object?</p> <p>This is the interface defition in IDL (compiled in C++ in VS 2005):</p> <pre><code> [ object, uuid(B60C546F-EE91-48a2-A352-CFC36E613CB7), dual, nonextensible, helpstring("IScriptGenerator Interface"), pointer_default(unique) ] interface IScriptGenerator : IDispatch{ [helpstring("Init the Script generator")] HRESULT Init(); [helpstring("General purpose error reporting")] HRESULT GetLastError([out] BSTR *Error); }; </code></pre> <p>This is the stub created for C# by Tlbimp:</p> <pre><code>[TypeLibType(4288)] [Guid("B60C546F-EE91-48A2-A352-CFC36E613CB7")] public interface IScriptGenerator { [DispId(1610743813)] void GetLastError(out string Error); [DispId(1610743808)] void Init(); } </code></pre> <p>This is part of the main C# code, creating a COM object by its ProgID and casting it to the IScriptGenerator interface:</p> <pre><code>public ScriptGenerator(string GUID) { Type comType = Type.GetTypeFromProgID(GUID); object comObj = null; if (comType != null) { try { comObj = Activator.CreateInstance(comType); } catch (Exception ex) { Debug.Fail("Cannot create the script generator COM object due to the following exception: " + ex, ex.Message + "\n" + ex.StackTrace); throw ex; } } else throw new ArgumentException("The GUID does not match a registetred COM object", "GUID"); m_internalGenerator = comObj as IScriptGenerator; if (m_internalGenerator == null) { Debug.Fail("The script generator doesn't support the required interface - IScriptGenerator"); throw new InvalidCastException("The script generator with the GUID " + GUID + " doesn't support the required interface - IScriptGenerator"); } } </code></pre> <p>And this is the implementing C# code, to test it's working (and it's not):</p> <pre><code> [Guid("EB46E31F-0961-4179-8A56-3895DDF2884E"), ProgId("ScriptGeneratorExample.ScriptGenerator"), ClassInterface(ClassInterfaceType.None), ComSourceInterfaces(typeof(SOAAPIOLELib.IScriptGeneratorCallback))] public class ScriptGenerator : IScriptGenerator { public void GetLastError(out string Error) { throw new NotImplementedException(); } public void Init() { // nothing to do } } </code></pre>
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