The extern alias 'xxx' was not specified in a /reference option

Question

I have two assemblies that unfortunately define the same type in the same namespace. I'm trying to use a an extern alias to work around the problem. In the Visual Studio IDE I have set the "Aliases" property of the reference to my alias. This is supposed to change the C# compiler command line to be something like this:

/reference:MyAlias=MyAssembly.dll 

But it doesn't actually do that. The Visual Studio IDE seems to just ignore the Aliases property setting on the reference. So when I go and add the line extern alias MyAlias; at the top of my C# code file I get the error that the alias was not specified in a /reference option to the compiler. I can't figure out what I am doing wrong. Any ideas?

Answer 1

I have the same problem and I was able to reproduce the issue.

It turns out reference aliases are ignored on projects containing xaml files which has an xmlns definition to the output assembly like xmlns:local='clr-namespace:TestProject'.

If you think this is your case as well, please vote up my bug report at Microsoft Connect.

EDIT: There is a suggested workaround in the link above which requires editing the project file manually. In order for this to work, I had to give full path of the assembly. Add the following instructions to the end of your project file:

<Target Name="solveAliasProblem" > <ItemGroup>  <ReferencePath Remove="FullPath.dll"/>  <ReferencePath Include="FullPath.dll">     <Aliases>ourAlias</Aliases>  </ReferencePath> </ItemGroup> </Target> <PropertyGroup>     <CoreCompileDependsOn>solveAliasProblem;$(PrepareResourcesDependsOn)</CoreCompileDependsOn> </PropertyGroup> 

Answer 2

Brian, I had the same problem as you and I figured out how to fix it.

I would do the same thing as you:

1. Use the properties window to change the alias for the assembly from 'global' to 'MyAlias'
2. At the top of the file where the aliased assembly is used, put extern alias MyAlias. This must be before any using statements.
3. Use the alias prefix to use the namespace you want, for example using MyAlias::MyNamespace.

And I would still get the error. After screwing around a bit, I figured out that the way to fix it is to set the referenced dll to a dll that is outside of the solution you are working in. Once I did that, the error message we were both seeing went away, and I was able to continue working on my project.

I hope that helps, happy coding!