Does a COM DLL have to be compiled and registered for each bit edition?

Question

Is it OK for a COM DLL to be compiled as AnyCPU and work with both 32 bit and 64 bit applications?

Yesterday I started writing a C# COM DLL so that my MFC project could use the DLL. The DLL itself is for using the GMail API.

Initially I was compiling the DLL as either x86 or x64 and both of my executables were running fine.

Then I decided to change the DLL to compile as AnyCPU and now when my program runs it says Class not registered.

Does the DLL have to be compiled for each Bit edition then?

Answer 1

No, you can keep the .DLL compiled as "Any CPU" (in fact I certainly recommend it as long as you can), but you must register it in each version of the registry, so for example using regasm:

64-bit:

c:\Windows\Microsoft.NET\Framework64\v4.0.30319\RegAsm.exe ClassLibrary1.dll /codebase /tlb

32-bit:

c:\Windows\Microsoft.NET\Framework\v4.0.30319\RegAsm.exe ClassLibrary1.dll /codebase /tlb