How to resolve " 'IAsyncActionWithProgress<>' is defined in an assembly that is not referenced" in Windows UAP app

Question

I am developing a Windows UAP app in Visual Studio Ultimate CTP 2015 (latest one available in site).

I am facing issues while using await on Functions returning IAsyncActionWithProgress<>, IAsyncAction<> , IAsyncOperation<> and IAsyncOperationWithProgress<>.

I am getting the following error

Error CS0012 The type 'IAsyncActionWithProgress<>' is defined in an assembly that is not referenced. You must add a reference to assembly 'Windows, Version=255.255.255.255, Culture=neutral, PublicKeyToken=null, ContentType=WindowsRuntime'.

I tried adding reference to the assembly mentioned (Windows). Even though this resolved the above error, it created another error at many other places (seems like there is a repetition of some classes/API's in both the assemblies. One of the error obtained is :

Error CS0433 The type 'Page' exists in both 'Windows.Foundation.UniversalApiContract, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null, ContentType=WindowsRuntime' and 'Windows, Version=255.255.255.255, Culture=neutral, PublicKeyToken=null, ContentType=WindowsRuntime'.

Example of code

Windows.Storage.FileProperties.BasicProperties fileSize = await file.GetBasicPropertiesAsync();

This was working fine for a Windows Phone 8.1 app in Visual Studio 2013. What is the change I have to make to get the same result in UAP App in Visual Studio 2015.

Answer 1

I had the same problem with the IAsyncAction and I have just managed to solve it, so I am going to share the (maybe not the best) solution.

First I tried repair VS, no success. Then reinstalling VS, again no success. So I went to control panel -> programs -> uninstall programs, and from there I uninstalled everything that had something to do with Visual Studio or .NET. It displayed me a couple of errors, like that some applications require this program to run, but i anyway uninstalled it (if I will need it I will install it again). After that I installed Visual Studio again, wrote the code which caused the error and, it worked, with no error.

Hope this helps you as it did help me.