Xamarin.Mac application targetting .NET Framework 4.7.1 gets incorrect references

[fschwiet]

Do you want to request a feature or report a bug?

bug

What is the current behavior?

When adding a reference to Nuget package ReactiveUI (which in turn pulls in Splat) to a Mac application that is targeting .NET framework 4.7.1 we end up with the wrong references in the project file (to things like PresentationFramework). I am creating this bug in the Splat repository because the libraries being pulled in are referenced from https://github.com/reactiveui/splat/blob/master/src/Splat/Splat.csproj#L35.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

An example project is here: https://github.com/fschwiet/MacSplatConsole/tree/xamarin-mac-full-presentationframework-reactiveui-9.6.3. In the below repro steps I will reference a corresponding commit you can look at.

• Create a Xamarin.Mac project from the Xamarin.Mac app template in Visual Studio for Mac. (fschwiet/MacSplatConsole@3c2b7cc)
• Change the Xamarin.Mac project to target "Xamarin.Mac full" / ".NET Framework 4.7.1". (fschwiet/MacSplatConsole@54af128)
• Add a reference to the ReactiveUI nuget package: (fschwiet/MacSplatConsole@811f83b)

You'll see in the last commit that some libraries like PresentationFramework and PresentationCore are targeted. The project still builds and runs, but if I try to use ReactiveUI it doesn't work.

As an example of things not working, if I add code:

using System;
using System.Reactive.Linq;
using ReactiveUI;
...
    Observable.Timer(TimeSpan.FromSeconds(3)).ObserveOn(RxApp.TaskpoolScheduler).Subscribe(

somewhere I get complaints about needing to add a reference to WindowsBase or System.Windows.Forms.

What is the expected behavior?

When I add the nuget package I should get libraries that are available to Xamarin.Mac applications.

What is the motivation / use case for changing the behavior?

I am going to error on giving you too much information below. The above repro I think isolates my concern though I suspect I am barking up the wrong tree.

We have some existing code using ReactiveUI we're trying to package into a UI-less app to run as an embedded service. We don't want to package this as a regular Xamarin.Mac application since that would spawn a window and add a system tray icon. I think most of our usages of ReactiveUI in the packaged code are related to scheduling (using the schedulers in RxApp).

So I went down the route of trying to create a console application with Xamarin.Mac bindings according to the instructions here: https://docs.microsoft.com/en-us/xamarin/mac/app-fundamentals/console. In short, the process is to create a .NET Console Project (.NET, not .NET core) and manually bind some things to get cocoa API support / Xamarin.Mac goodness. Such projects have the same targeting issues as the project created in these repro steps (the target framework rule for net461 in splat.csproj is invoked).

I thought I could resolve the targeting issues by referencing DLLs directly, bypassing nuget (inspired by https://stackoverflow.com/questions/49598467/how-to-choose-target-framework-from-nuget-package). So I created a regular .Mac app alongside the console app, added the nuget package to the regular app then ported the changes over to the console app so I could choose the DLLs being used. This didn't quite work, the last error I ran into was that it couldn't find System.Reactive.dll.

Which versions of ReactiveUI, and which platform / OS are affected by this issue? Did this work in previous versions of ReativeUI? Please also test with the latest stable and development snapshot

macOS High Sierra 10.13.6,
xCode version 10.1,
Visual Studio for Mac 7.7.2
Xamarin.Mac tooling v5.2.1.12

Other information (e.g. stacktraces, related issues, suggestions how to fix)

Thanks for all the hard work on ReactiveUI. There is an existing closed issue #48 with similar symptons, but its from 2014 so I'm not sure how related it is.

[clairernovotny]

If you're targeting .NET 4.7.1, then there's nothing we can do. We have a Xamarin.Mac target, but if it's not choosing that one, the bug is either in NuGet or VSfM.

[fschwiet]

If you're targeting .NET 4.7.1, then there's nothing we can do

I presume this statement applies to .NET 4.6.1 and 4.7 as well (these won't work either) but if I'm mistaken let me know.

[clairernovotny]

That's correct. The Xamarin.Mac app needs to use the Xamarin.Mac target in the package as that's the one that has the right references for that platform.

[fschwiet]

I just wanted to explicitly call out the change in target in the repro mac app that is problematic:

In commit fschwiet/MacSplatConsole@54af128 the targeting changes from:

    <TargetFrameworkVersion>v2.0</TargetFrameworkVersion>
     <TargetFrameworkIdentifier>Xamarin.Mac</TargetFrameworkIdentifier>

to

     <TargetFrameworkVersion>v4.7.1</TargetFrameworkVersion>
     <UseXamMacFullFramework>true</UseXamMacFullFramework>

I'm not sure nuget can do a better job. I wonder if its looking for the target monomac (https://docs.microsoft.com/en-us/nuget/reference/target-frameworks) and not finding it, if thats the case I wonder if Splat.csproj could reference functioning libraries for that target (it could be this scenario is completely unworkable).

Sorry just thinking aloud on this one as I'll need to come back to investigate.

Target Frameworks Reference for NuGet

NuGet target framework references identify and isolate framework-dependent components of a package.

[clairernovotny]

This has been a long-standing issue that the NuGet team refuses to fix:

NuGet/Home#2662

[fschwiet]

Oren thank you for sharing your knowledge on these things.

[glennawatson]

I would recommend you upvote that nuget issue if you can.