Building an UWP app from unity, using external dll built in visual studio, generates an error on the Task class

Question

I made an UWP application in Unity for Hololens and I added in the Assets a class using Tasks (System.Threading.Tasks). The code of the class is surrounded by the compilation directive as follow:

#if WINDOWS_UWP
.... Code Here
#endif

since it needs to work only on the device.

I successfully deployed the application on the Hololens.

But when I try to move the class in an external dll, generated compiling a Class Library (Universal Windows) project in Visual studio, and I reference it in Unity, when compiling I get the following error:

... type 'Task<>' claims it is defined in 'System.Runtime', but it could not be found.

It seems that it is not using System.Threading.Tasks, but it tries to use a Task class defined in System.Runtime.

Why this happens only if the class is in an external dll and I works when the class is directly in the assets folder?

Since I need to have the code in the external dll how can I fix it?

Answer 1

The problem was in the minimun SDK version of the UWP library.

By default Unity uses Windows 10 (10.0; Build 10240) when building UWP applications, while the minimum version of the UWP Library was Windows 10 Creators Update (10.0; Build 15063) .

Setting up the SDK minimum version of the UWP Class library in visual studio to Windows 10 (10.0; Build 10240) , and reimporting the dll in Unity, solved my problem.