MSBuild.Sdk.Extras

This package contains a few extra extensions to the SDK-style projects that are currently not available in the main SDK. That feature is tracked here: dotnet/sdk#491

The primary goal is to enable multi-targeting without you having to enter in tons of properties within your csproj, thus keeping it nice and clean.

See this blog article for some background on how to get started. Installing this package, MSBuild.Sdk.Extras adds the missing properties so that you can use any TFM you want.

In short: Create a new .NET Standard class library in VS 2017. Then you can edit the TargetFramework to a different TFM (after installing this package), or you can rename TargetFramework to TargetFrameworks and specify multiple TFM's with a ; separator. After building, you can use the pack target to easily create a NuGet package: msbuild /t:pack ...

Few notes:

This will only work in VS 2017, Visual Studio for Mac. It's possible it will work in Code, but only as an editor.
To compile, you'll need the desktop build engine -- msbuild.exe. Most of the platforms rely on tasks and utilities that are not yet cross platform
You must install the tools of the platforms you intend to build. For Xamarin, that means the Xamarin Workload; for UWP install those tools as well.

NuGet: MSBuild.Sdk.Extras

CI feed is on MyGet: https://www.myget.org/F/msbuildsdkextras/api/v3/index.json

Using the Package

To use this package, add a PackageReference to your project file like this (specify whatever version of the package or wildcard):

<PackageReference Include="MSBuild.Sdk.Extras" Version="1.0.5" PrivateAssets="all" />

Setting PrivateAssets="all" means that this build-time dependency won't be added as a dependency to any packages you create by using the Pack targets (msbuild /t:pack or dotnet pack).

Then, at the end of your project file, either .csproj or .vbproj, add the following Import just before the closing tag

<Import Project="$(MSBuildSDKExtrasTargets)" Condition="Exists('$(MSBuildSDKExtrasTargets)')" />

This last step is required until dotnet/msbuild#1045 is resolved.

Targeting UWP

If you plan to target UWP, then you must include the UWP meta-package in your project as well, something like this:

<ItemGroup Condition=" '$(TargetFramework)' == 'uap10.0' "> 
  <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform " Version="5.2.3" /> 
</ItemGroup>

Targeting Tizen

If you plan to target Tizen, then you should include the following meta-package:

<ItemGroup Condition=" '$(TargetFramework)' == 'tizen30' ">  
  <PackageReference Include="Tizen.NET" Version="3.0.0" />
</ItemGroup>

Targeting UWP, Windows 8, Windows Phone, etc using the 1.0 SDK tooling

If you're targeting a WinRT platform and you use the pack target, there's an important workaround needed to ensure that the .pri files are included in the package correctly. When you call pack, you also must override NuGetBuildTasksPackTargets on the command-line to ensure the fixed targets get applied. The value you specify must not be a real file.

For example: msbuild my.csproj /t:pack /p:NuGetBuildTasksPackTargets="workaround"

GitHub issue NuGet/Home#4136 is tracking this. This is fixed in the 2.0 SDK tooling and is no longer needed there.

Single or multi-targeting

Once this package is configured, you can now use any supported TFM in your TargetFramework or TargetFrameworks element. The supported TFM families are:

netstandard (.NET Standard)
net (.NET Framework)
netcoreapp (.NET Core App)
wpa (Windows Phone App 8.1)
win (Windows 8 / 8.1)
uap (UWP)
wp (Windows Phone Silverlight, WP7+)
sl (Silverlight 4+)
tizen (Tizen 3.0+)
xamarinios / Xamarin.iOS
monoandroid
xamarinmac / Xamarin.Mac
xamarinwatchos / Xamarin.WatchOS
xamarintvos / Xamarin.TVOS
portable- (legacy PCL profiles like portable-net45+win8+wpa81+wp8)

For legacy PCL profiles, the order of the TFM's in the list does not matter but the profile must be an exact match to one of the known profiles. If it's not, you'll get a compile error saying it's unknown. You can see the full list of known profiles here: https://portablelibraryprofiles.stephencleary.com/.