Visual Studio (Xamarin): DependencyService + Nuget + iOS = Fail - ios

Question

We are writing a Visual Studio (Xamarin) cross-platform application that will share quite a bit of functionality with the next application we write, so we wanted to put that shared functionality into a "library" so we could test it, share it easily, etc.
The only way we found to write a cross-platform library, is to create it using the standard Xamarin DependencyService paradigm, turn it into a NuGet package, and then load that package into our main app. For better or worse, we did this before Microsoft provided a template for generating NuGet libraries like this, so we had to roll it ourselves.
This works fine for Android, but now I'd like to get the same code working for iOS and it's simply not working. No errors, no warnings, but when I run the app and call
Client = DependencyService.Get<IClient>();
It simply returns null. If I look at the Output/Debug window, it is loading the 'Company.Client.Abstractions.dll' (the root DLL containing the definition of IClient) but not the iOS-specific 'Company.Client.dll' (which contains the iOS-specific implementation of IClient).
Here's my nuspec file:
<?xml version="1.0"?>
<package >
<metadata>
<id>Client</id>
<version>0.0.35</version>
<authors>Me</authors>
<owners>Company</owners>
<requireLicenseAcceptance>false</requireLicenseAcceptance>
<description>Stuff</description>
<releaseNotes>Initial release</releaseNotes>
<copyright>Copyright 2017 Company</copyright>
<dependencies>
<group targetFramework="MonoAndroid">
<dependency id="Xamarin.Forms" version="2.3.4.247" />
</group>
<group targetFramework="Xamarin.iOS10">
<dependency id="Xamarin.Forms" version="2.3.4.247" />
</group>
<group targetFramework="uap">
<dependency id="Xamarin.Forms" version="2.3.4.247" />
</group>
</dependencies>
</metadata>
<files>
<!-- Cross-platform reference assemblies -->
<file src="Company.Client.Abstractions\bin\Debug\Company.Client.Abstractions.dll" target="lib\portable-net45+win+wpa81+wp80+MonoAndroid10+xamarinios10+MonoTouch10\Company.Client.Abstractions.dll" />
<file src="Company.Client.Abstractions\bin\Debug\Company.Client.Abstractions.pdb" target="lib\portable-net45+win+wpa81+wp80+MonoAndroid10+xamarinios10+MonoTouch10\Company.Client.Abstractions.pdb" />
<!-- iOS reference assemblies -->
<file src="Company.Client.iOS\bin\iPhone\Debug\Company.Client.dll" target="lib\Xamarin.iOS10\Company.Client.dll" />
<file src="Company.Client.iOS\bin\iPhone\Debug\Company.Client.pdb" target="lib\Xamarin.iOS10\Company.Client.pdb" />
<!-- Android reference assemblies -->
<file src="Company.Client.Android\bin\Debug\Company.Client.dll" target="lib\MonoAndroid10\Company.Client.dll" />
<file src="Company.Client.Android\bin\Debug\Company.Client.pdb" target="lib\MonoAndroid10\Company.Client.pdb" />
<!-- UWP reference assemblies -->
<file src="Company.Client.UWP\bin\Debug\Company.Client.dll" target="lib\UAP10\Company.Client.dll" />
<file src="Nuvectra.Client.UWP\bin\Debug\Company.Client.pdb" target="lib\UAP10\Company.Client.pdb" />
</files>
</package>
I'm thinking there are two classes of possible problems:
I'm generating the DLL wrong
I'm generating the application wrong
Looking at the generated DLLs, the Android DLL is 28k long, the iOS DLL is 23k, so it doesn't look like the iOS DLL is empty. Is there a tool that would let me inspect the iOS DLL and make sure it has the necessary entry point(s)?
The Project that generates the iOS DLL has these settings:
Target framework: Xamarin.iOS
Output type: Class Library
Condition compilation symbols: __ UNIFIED__;__ MOBILE__;__ IOS__
Platform: Active (Any CPU)
The application that is using the DLL has these settings for the iOS Project:
SDK Version: Default
Linker Behavior: Don't Link
Platform: Active (iPhone)
Supported Architectures: ARMv7 + ARM64
Target framework: Xamarin.IOS
Output type: Console Application
Conditional compilation symbols: __ UNIFIED__;__ MOBILE__;__ IOS__
The interface definition in my 'Abstractions' project looks like this:
namespace Company.Client
{
public abstract class IClient
{
void abstract function();
}
}
and the implementation in my iOS project looks like this:
using Company.Client.iOS;
[assembly: Xamarin.Forms.Dependency (typeof (IosClient))]
namespace Company.Client.iOS
{
public class IosClient : IClient
{
void override function();
}
}

Answer 1

We tried many different ways to create a NuGet package with platform-specific code loaded using DependencyService and every single way had the same problem - worked fine under Android, failed under iOS.
The solution is to create a class in the iOS library that is not loaded using DependencyService, and then in the iOS application, create an instance of that class. That's enough to convince the iOS application that it actually needs to load the iOS library DLL, and then the rest of the DependencyService magic works correctly.