Using Xamarin Forms with .NET Standard

With the release of .NET Core and the .NET Standard Library last week, many people want to know how they can use packages targeting netstandard1.x with their Xamarin projects. It is possible today if you use Visual Studio; for Xamarin Studio users, support is coming soon.

Prerequisites

Using .NET Standard pretty much requires you to use project.json to eliminate the pain of "lots of packages" as well as properly handle transitive dependencies. While you may be able to use .NET Standard without project.json, I wouldn't recommend it.

You'll need to use the following tools:

Getting Started

As of now, the project templates for creating a new Xamarin Forms project start with an older-style packages.config template, so whether you create a new project or have an existing project, the steps will be pretty much the same.

Step 1: Convert your projects to project.json following the steps in my previous blog post.

Step 2: As part of this, you can remove dependencies from your "head" projects that are referenced by your other projects you reference. This should simplify things dramatically for most projects. In the future, when you want to update to the next Xamarin Forms version, you can update it in one place, not 3-4 places. It also means, you only need the main Xamarin.Forms package, not each of the packages it pulls in.

If you hit any issues with binaries not showing up in your bin directories (for your Android and iOS "head" projects), make sure that you have set CopyNuGetImplementations to true in your csproj as per the steps in the post.

At this point, your project should be compiling and working, but not yet using netstandard1.x anywhere.

Step 3: In your Portable Class Library projects, find the highest .NET Standard version you need/want to support.

Here's a cheat sheet:

  • If you only want to support iOS and Android, you can use .NET Standard 1.6. In practicality though, most features are currently available at .NET Standard 1.3 and up.
  • If you want to support iOS, Android and UWP, then NET Standard 1.4 is the highest you can use.
  • If you want to support Windows Phone App 8.1 and Windows 8.1, then NET Standard 1.2 is your target.
  • If you're still supporting Windows 8, .NET Standard 1.1 is for you.
  • Finally, if you need to support Windows Phone 8 Silverlight, then .NET Standard 1.0 is your only option.

Once you determine the netstandard version you want, in your PCL's project.json, change what you might have had:

{
    "dependencies": {
        "Xamarin.Forms": "2.3.0.107"        
    },
    "frameworks": {        
        ".NETPortable,Version=v4.5,Profile=Profile111": { }
    },
    "supports": { }
}

to

{
    "dependencies": {
        "NETStandard.Library": "1.6.0",
        "Xamarin.Forms": "2.3.0.107"        
    },
    "frameworks": {        
        "netstandard1.4": {
            "imports": [ "portable-net45+wpa81+wp8+win8" ]
         }
    },
    "supports": { }
}

Note the addition of the imports section. This is required to tell NuGet that specified TFM is compatible here because the Xamarin.Forms package has not yet been updated to use netstandard directly.

Then, edit the csproj to set the TargetFrameworkVersion element to v5.0 and remove any value from the TargetFrameworkProfile element.

At this point, when you reload the project, it should restore the packages and build correctly. You may need to do a full clean/rebuild.

Seeing it in action

I created a sample solution showing this all working over on GitHub. It's a good idea to clone, build and run it to ensure your environment and tooling is up-to-date. If you get stuck converting your own projects, I'd recommend referring back to that repo to find the difference.

As always, feel free to tweet me @onovotny as well.