CODEWITHSUNDEEP
c#com.net-8.0com-interop
Palo
Palo

Reputation: 1081

How to not use builtin com interop to make trimming work in .NET

In C# .NET 8 given a pointer (IntPtr) to a native object implementing a COM-compatible interface and a C# interface definition, how do I convert the pointer to an object implementing such interface without using built-in COM to enable trimming?

Background:

I have a small C# app (.NET 8) which uses a COM library via autogenerated bindings from tlb. I would like to publish a standalone exe and use .NET's trimming option <PublishTrimmed> to make the exe's size reasonable.

The .NET built-in com interop does not support trimming. I have found a subset of dlls to mark not trimmable to make the app run. However, that still generates a lot of warnings and is I believe technically unsupported by .NET and can break in later .NET versions.

The COM DLL doesn't actually require full COM, it just uses COM-compatible API. All I need is to call a P/Invoke method which returns a pointer to a COM-like object, which matches the autogenerated tlb interface. How would I convert that pointer to an object implementing a particular C# COM-compatible interface using only features supported by trimming?

// auto generated from tlb
[ComImport]
[Guid(<guid>)]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ISomeInterface
{
    [MethodImpl(MethodImplOptions.InternalCall, MethodCodeType = MethodCodeType.Runtime)]
    void method([In][MarshalAs(UnmanagedType.LPWStr)] string input, out int pbData);
    ...
}

// my (simplified) current code using built in com interop
void GetInstance([MarshalAs(UnmanagedType.Interface)] out object createdObject);

GetInstance(out object comObject);
return comObject as ISomeInterface ?? throw new InvalidOperationException("Failed to create ISomeInterface instance.");

Upvotes: 0

Views: 39

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