LA0194: Aspect Implements IAspect from Another Assembly

Cause

At build time, PostSharp creates an instance of each aspect applied to the project and casts it to the IAspect interface of the PostSharp assembly that the compiler loaded. PostSharp reports LA0194 when this cast fails although the aspect implements an interface with the same full name, PostSharp.Aspects.IAspect: the interface that the aspect implements comes from another assembly, typically another version or another copy of PostSharp.dll.

The three placeholders are assembly-qualified names. <AspectType> is the aspect type, <FoundInterface> is the interface that it implements, and <ExpectedInterface> is the interface of the PostSharp assembly of the compiler. Compare the versions and the public key tokens of the last two to find the assembly that does not match.

This message depends on the PostSharp assemblies that the build references and loads, which a test cannot vary, so no example can show it.

Resolution

• Reference a single version of the PostSharp packages in all the projects of the solution, including the projects that define aspects, and rebuild them all. Central package management, with a Directory.Packages.props file, keeps the versions aligned.
• Remove direct references to a PostSharp.dll file (a Reference item with a HintPath) and reference the PostSharp package instead.
• When the aspect comes from a library, check which version of PostSharp the library references.
• Run dotnet list package --include-transitive to find the packages that bring another version of PostSharp.

See Also

Reference

IAspect

Other Resources

Developing Simple Aspects