Import Qt dll in C#

[Andrea]

Hi everybody,

I'm getting stucked trying to import and use a Qt class, deployed as dll library, in a Visual Studio C# solution.
I've googled a lot, and found many different possible advices on how to "solve" this issue: who tells to register dll as COM, who tells to make a C# wrapper, who to call dllimport, and many other.
Also Qt "official" tutorial seems to be quite old (still using MC++).
In all C# solution tested, also the simplest one with just one form and a button, still getting error:

"A reference to [dll_path] could not be added. Please make sure that the file is accessible, and that is a valid assembly or COM component"

Many thanks

[JonB]

@Andrea
Unless an expert here knows different and offers you a solution example, that message is telling you that you do indeed need either a native .NET assembly or a COM component and you will need to try the Googles you've found for one that works....

[mrdebug]

Hi Andrea. This is a method exported by a Qt dll

extern "C" DLLTESTSHARED_EXPORT int Somma(DllTest *&dlltest, int a, int b);

and this is the way to have it in a c# source

[DllImport(@"C:\Cpp\dllTest\dllTest-build-desktop\release\dllTest.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int Somma(ref IntPtr ptr, int a, int b);

[Andrea]

@mrdebug Thanks for your reply. I've seen how to "export" a method, but is possible doing something similar for unmanaged classes?

I know that I should create a C++/CLI wrapper, but my question is: if I'm not able to import the DLL, and therefore the class, how can I wrap it?

[mrjj]

@Andrea
Hi
In older times it was not possible to export a true class from c++ to c#.
Newer visual studio might be able to tricks
i dont know about to make work, so take this with a grain of salt.

However, back then you would wrap the class and use a function based
proxy-like design to create and use
classes in the dll and not directly in c#.
Like here
https://stackoverflow.com/questions/315051/using-a-class-defined-in-a-c-dll-in-c-sharp-code
the PInvoke version.

[Pangolin]

@mrdebug said in Import Qt dll in C#:

DLL
This is the right answer.