防止在工作目录中加载dll，InvalidCastException类型A不能强制转换为类型B

Question

Is it possible to prevent the loading of a dll that is in the working directory and force it to use a dll somewhere else that I specify?

I am trying to run some unit tests and am getting this InvalidCast exception:

[A]AssemblyA.DataType cannot be cast to [B]AssemblyA.DataType. Type A originates from 'AssemblyA, Version=1.0.4645.21698, Culture=neutral, PublicKeyToken=null' in the context 'LoadFrom' at location 'E:\\webservice\\bin\\AssemblyA\\AssemblyA.dll'. Type B originates from 'AssemblyA, Version=1.0.4645.21698, Culture=neutral, PublicKeyToken=null' in the context 'Default' at location 'E:\\TestResults\\Out\\AssemblyA.dll'.

On test startup, it calls some initialization code that uses Assembly.LoadFrom to load a dll from E:\\webservice\\bin\\AssemblyA\\AssemblyA.dll and create some of the types and put them in a cache.

There are post build events that xcopy the dlls to that location, so they are exactly the same dll in both locations.

But the unit test is running from the working directory of E:\\testresults\\out\\ so it automatically loads the AssemblyA.dll there, ignoring the assembly already loaded, without ever giving me a chance to intercept that load with the Appdomain.AssemblyResolve event

So when the unit test code tries to retrieve an object from the cache that was put there from the E:\\webservice\\bin\\AssemblyA\\AssemblyA.dll it says invalid cast because its expecting the type from E:\\TestResults\\Out\\AssemblyA.dll

After looking over Best Practices for Assembly Loading it seems like there is no way to prevent it from loading the dll from the working directory, even though I already manually loaded the dll I want to use. Are there any options besides changing the application to not load from E:\\webservice\\bin... at all?

(Using LoadFile or Load byte[] both also result in the same error)

Answer 1

Now, I try to help you out of you problem..

I recommended to sign your assembly with a StrongName .

The CLR use this to identify the assembly. This is not almost solving your problem. But to solve your problem I suggest to use an interface to encapsulate your diffrent types. So, You can store any type in your cache and return only the intrerface, and the cast is gone.

If this is not solving your problem, you must provide me more information.

Answer 2

As Panos suggested in the comment above, this was solved by setting CopyLocal=false on the referenced assemblies. That way the CLR can't attempt to load the dll from the working directory because the dll isn't there.