Visual Studio 2015 - C# Windows Universal App missing assembly reference

Question

Today I cloned my windows universal app project from github onto a new machine running a new install of Visual Studio 2015.

After the project loaded, I noticed that all of my pages and properties were underlined red with many errors

CS0246 C# The type or namespace name "<name>" could not be found (are you missing a using directive or an assembly reference?)

as well as others such as

CS0518 C# Predefined type 'System.Void' is not defined or imported

CS0012 C# The type '' is defined in an assembly that is not referenced. You must add a reference to assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

CS1545 C# Property, indexer, or event 'Application.Suspending' is not supported by the language; try directly calling accessor methods 'Application.add_Suspending(SuspendingEventHandler)' or 'Application.remove_Suspending(EventRegistrationToken)'

I noted that CS0012 actually gives information about what is needed to address the issue:

You must add a reference to assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

Looking in my project.json file, however, I could see

"dependencies": {
    "Microsoft.NETCore.UniversalWindowsPlatform": "5.0.0"
}

As a result the project will not build or run, just lists lots of errors, how can you fix this?

Answer 1

Looking in the References of the project in the Solution Explorer it can be seen that even though Microsoft.NETCore.UniversalWindowsPlatformis listed as a dependency, it's missing from the project and this is causing the issue.

Visual studio knows that the assembly is a dependency and needs to be referenced but it doesn't seem to come preinstalled with Visual Studio 2015, even when you install all of the Windows 10 development tools during setup, and it doesn't seem to autofetch the package even when it knows it needs it!

To fix, you need to manually install the package using NuGet and it will then be resolved correctly as a reference.

To do this, right click on References, then click Manage NuGet Packages....

On the NuGet Package Manager screen, search for Microsoft.NETCore.UniversalWindowsPlatform and it will be an exact match.

Click on Install in the details pane on the right hand side and Visual Studio will fetch the package and include it as a reference in your project

The red underlining will then all disappear and you can continue working on your project!

Answer 2

I had similar problem. universal project I create my self had reference there. Some of the samples for windows iot sites didn't have reference when downloaded. NUGET said it was already installed. for me the solution was to build the solution and it repaired itself.