尝试实例化位于可执行文件中的COM对象时，COM Interop：System.InvalidCastException

Question

Using COM interop, I have following exception in my C# client code when trying to instantiate a COM object coded in C++ compiled and running in a COM executable server: System.InvalidCastException: Unable to cast object of type 'System.__ComObject' to type "XXX". (Where XXX was the class type used in my C# code for the COM object)

The executable containing the COM object runs on the same machine as the client code. I have verified that the COM object is registered properly in the windows registry.

The instantiation fails not systematically in my project. I need to execute at least 3 times to see the failure. I have the same issue during the tests running in our CI system.

Answer 1

The problem is solved: 2 assemblies were used by my project that had references to the Interop dll used to instantiate the COM object. One of these 2 assemblies had “EmbedInteropTypes” set to true and the other one had the same property set to false. Putting “EmbedInteropTypes” to false for both fixed the problem.

I am still looking for good explanations on why this did not work. I have found other projects where similar issues happened it seems: https://github.com/yck1509/ConfuserEx/issues/302