How to get WPF XAML Designer to play nicely with IValidatableObject from NET Standard 2.0 libraries? - wpf

Question

Background:
using Visual Studio 2017 v15.4 (no ReSharper or any weird extensions)
Repro solution includes 2 projects:
WPF project: .NET 4.6.1, using NuGet PackageReference format
Class library: NET Standard 2.0
Both projects have the System.ComponentModel.Annotations NuGet package installed.
Problem
After upgrading my WPF project's NuGet format from the old packages.config to the new PackageReference, I started experiencing design-time errors:
Or sometimes the harsher flavor:
To start with, the following ViewModel code works fine:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
public class MainWindowViewModel
{
public ValClass MyProp => new ValClass();
}
public class ValClass : IValidatableObject
{
//Implementation stuff
}
However, if I then define an identical class in my NET Standard project, and include that as a type in my ViewModel, it produces the error.
Comparing an F12 on the IValidatableObject of these 2 classes:
The WPF version:
#region Assembly System.ComponentModel.DataAnnotations, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35
// C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.1\System.ComponentModel.DataAnnotations.dll
#endregion
The NET Standard 2.0 version:
#region Assembly System.ComponentModel.Annotations, Version=4.2.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a
// C:\Users\a0110\.nuget\packages\system.componentmodel.annotations\4.4.0\ref\netstandard2.0\System.ComponentModel.Annotations.dll
#endregion
It's clear that the same type and namespace are defined in assemblies with different names--not just assembly versions.
How can I get the XAML Designer to successfully locate whatever assembly is required to use IValidatableObject?
Things I have Tried
Installing VS v15.5 preview and targeting the WPF project to .NET 4.7 (also 15.5 preview 2 and 3, .NET 4.7.1)
Adding the old System.ComponentModel.DataAnnotations reference to the WPF project (with and without the NuGet version)
reverting back to packages.config format (this didn't actually succeed; it appears that I'm stuck with PackageReference!)
grabbing a copy of the System.ComponentModel.Annotations.dll from the project's output folder and referencing it directly (VS would not let me do this)
adding a bindingRedirect to my App.config
adding <DependsOnNETStandard>True</DependsOnNETStandard> to the .csproj
adding <DependsOnNETStandard>netstandard2.0</DependsOnNETStandard> to .csproj
adding <_HasReferenceToSystemRuntime>true</_HasReferenceToSystemRuntime> to .csproj
adding the NETStandard.Library NuGet package to the WPF project
Update
For anyone else who is plagued by this issue, I have found a workaround:
Locate the System.ComponentModel.Annotations.dll on your hard drive that your NET Standard project uses for IValidatableObject. Copy it to a location within your project.
Uninstall the System.ComponentModel.Annotations NuGet package from your solution
Give your NET Standard project a direct reference to DLL you copied
Give your WPF project a reference to the standard assembly System.ComponentModel.DataAnnotations
Upgrade your WPF project to target .NET 4.7.1
Compile. Your WPF design-time should be free from this error.
.