Using C# with an old API object

Administrator

I am trying to do some coding in C# against an API object that has not been updated to be fully COM compliant. It does not appear to have a valid type library in the dll. My problem is that I can get everything to work in VB6 and VB.Net without having any reference to the API object. Obviously, Intellisense does not work, but the programs will compile and run with no problem. All calls into the API work just as documented in the API documentation. In C#, I can't compile anything without a reference to the object. I can't set up a reference, since there is no type library. Is there a way to get C# to compile without the reference? All I get is the compiler error "The type or namespace name 'OfficeTalk' could not be found (are you missing a using directive or an assembly reference?)" Am I missing something here? Thanks, Trent

4 Replies

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jcity44422y ago
I suspect you are not marshaling the parameters correctly. Post one of the methods you aret trying to use and I'm sure someone can give you an example on how to do it. -Mike G.
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zfjaj22y ago
I have a similar situation: From VB.NET I want to access Module methods from a COM Dll created from C++ source. I have succeeded using the DllImport(Attribute) concept, if the method has no parameters. I got NullReferenceException, when the method has String input/output parameters. So Suspects 1,3 can be excluded from my opinion. Have you further ideas for reason and correction of this problem? I would appreciate an answer also, if you found no solution.
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normanordas22y ago
I created an app in VB.Net that calls an old API i.e. a DLL file that is not fully COM compliant and therefore can't be imported to assembly code nor it can be reference as a COM inside VS.Net. What i did is use P/Invoke using DllImport. I was successful at doing that and most of the methods/functions were working except for some methods that when called returns System.NullReferenceException. Why is that then? Suspects: 1. COM Module method/function call inside VB.Net not supported i.e. only COM Class method/function is allowed. 2. Passing object to arguments but has no object reference yet (unfortunately its all value-types and not reference types so NullReferenceException is not possible) 3. COM can't expose methods/functions declared inside a Module Please advise! Tnx!
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Administrator23y ago
If your dll does not have a type library or is not callable through COM then you need to import the API using the DllImport attribute. Then you need to declare the api calls you want to use as external and then you can call them in your program. e.g. [DllImport("User32.dll")] public static extern int MessageBox(int h, string m, string c, int type);
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