How can C# use a legacy DLL simply without registration(regsvr32)

For my original answer to a similar question see: TFS Build server and COM references - does this work?

A good way to compile .NET code that references COM components without the COM components being registered on the build server is to use the COMFileReference reference item in your project/build files instead of COMReference. A COMFileReference item looks like this:

<ItemGroup>
  <COMFileReference Include="MyComLibrary.dll">
    <EmbedInteropTypes>True</EmbedInteropTypes>
  </COMFileReference>
</ItemGroup>

Since Visual Studio provides no designer support for COMFileReference, you must edit the project/build file by hand.

During a build, MSBuild extracts the type library information from the COM DLL and creates an interop assembly that can be either standalone or embedded in the calling .NET assembly.

Each COMFileReference item can also have a WrapperTool attribute but the default seemed to work for me just fine. The EmbedInteropTypes attribute is not documented as being applicable to COMFileReference, but it seems to work as intended.

See https://docs.microsoft.com/en-ca/visualstudio/msbuild/common-msbuild-project-items#comfilereference for a little more detail. This MSBuild item has been available since .NET 3.5.

It's a shame that no-one seems to know anything about this technique, which to me seems simpler than the alternatives. It's actually not surprising since I could only find just the one above reference to it on-line. I myself discovered this technique by digging into MSBuild's Microsoft.Common.targets file.

There's a walkthrough on registration-free COM here:

http://msdn.microsoft.com/en-us/library/ms973913.aspx

And excruciating detail here: http://msdn.microsoft.com/en-us/library/aa376414 (the root of that document is actually here: http://msdn.microsoft.com/en-us/library/dd408052 )

Also, for building in general, you should be able to use Tlbimp or tlbexp to create a TLB file that you can use for building, assuming the point of registering is just to be able to compile successfully, and not to run specific tests.