Mixing WPF project and ASP.Net Core Class Library causes build errors

I have an existing WPF application which I’ve converted from .NET Framework to .NET Core 3.1. I’m trying to add a REST API to this application which shares data so it’s desired to have it in the same process. The current design has the REST API as a class library project (also .NET Core 3.1) and run it on a separate thread started from the WPF app.

When a project reference to the API library is added to the WPF application it fails to build. If the reference is removed it builds just fine.

Here are the build errors:

Error	MC1000	Unknown build error, 'Could not find type 'System.Web.PreApplicationStartMethodAttribute' in assembly 'C:\Program Files\dotnet\packs\Microsoft.NETCore.App.Ref\3.1.0\ref\netcoreapp3.1\System.Web.dll'.' 	AVIF	C:\Program Files\dotnet\sdk\3.1.101\Sdks\Microsoft.NET.Sdk.WindowsDesktop\targets\Microsoft.WinFX.targets	225	
Error	CS1061	'App' does not contain a definition for 'InitializeComponent' and no accessible extension method 'InitializeComponent' accepting a first argument of type 'App' could be found (are you missing a using directive or an assembly reference?)	AVIF	C:\Users\kgillibrand\Documents\Work\Source\VtmInterfaces\AvlGpsApp\AVIF\App.xaml.cs	53	Active
Error	CS0039	Cannot convert type 'System.Windows.Window' to 'AVIF.MainWindow' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion	AVIF	C:\Users\kgillibrand\Documents\Work\Source\VtmInterfaces\AvlGpsApp\AVIF\App.xaml.cs	234	Active

I assume the 1st error is the most relevant.

Is this scenario supported? Are there .csproj changes that I need to make?

Here are the csproj files. WPF App Rest API

Thanks

[Pilchie]

It’s difficult to mix the two in the same project, because they have different targets pulled in by their different SDKs. I think the recommendation is to put one in a separate project and have a project reference to it from the other.

Moving to the SDK repo though.

[marcpopMSFT]

Closing old issues, please reactivate if this is still a problem.