How do you multi-target a .NET Core class library with csproj?

Question

When .NET Core still used the project.json format, you could build a class library targeting multiple frameworks (e.g. net451, netcoreapp1.0).

Now that the official project format is csproj using MSBuild, how do you specify multiple frameworks to target? I am trying to look for this from the project settings in VS2017, but I am able to only target a single framework from the .NET Core frameworks (it doesn't even list the other full .NET Framework versions which I do have installed):

Answer 1

You need to manually edit the project file and add s to the default TargetFramework and basically change it to TargetFrameworks. Then you mention the Moniker with a ; separator.

Also you can put the Nuget package references in a conditional ItemGroup manually or using VS Nuget Package Manager.

Here is what your .csproj should look like:

<Project Sdk="Microsoft.NET.Sdk">   <PropertyGroup>     <TargetFrameworks>netstandard1.6;net452</TargetFrameworks>   </PropertyGroup>    <ItemGroup Condition="'$(TargetFramework)' == 'net452'">     <PackageReference Include="Microsoft.Azure.DocumentDB">       <Version>1.12.0</Version>     </PackageReference>   </ItemGroup>    <ItemGroup Condition="'$(TargetFramework)' == 'netstandard1.6'">     <PackageReference Include="Microsoft.Azure.DocumentDB.Core">     <Version>1.1.0</Version>     </PackageReference>   </ItemGroup> </Project> 

Another workaround I do these days because of missing documentation is that I create a project in VS2015 and form the project.json using the available documentation and intellisense, then open the solution in VS2017 and use the built-in upgrade. I will then look at the csproj file to figure out how to make that configuration happen.

Multi-targeting more esoteric targets without a Moniker:

Microsoft:

PCLs are not recommended+

Although PCLs are supported, package authors should support netstandard instead. The .NET Platform Standard is an evolution of PCLs and represents binary portability across platforms using a single moniker that isn't tied to a static like like portable-a+b+c monikers.

If you want to target a Portable Profile it doesn't have a predefined moniker so Portable Profiles also can't infer TargetFrameworkIdentifier, TargetFrameworkVersion, and TargetFrameworkProfile. Also a compiler constant isn't defined automatically. Finally you have to add all assembly references none are provided by default.

This Example below is taken from a project that used the dynamic keyword so it additionally needed the Microsoft.CSharp assembly, thus you can see how it's references for different targets.

<Project Sdk="Microsoft.NET.Sdk">   <PropertyGroup>     <TargetFrameworks>netstandard1.5;net40;portable40-net45+sl5+win8+wp8</TargetFrameworks>   </PropertyGroup>    <PropertyGroup Condition="'$(TargetFramework)'=='portable40-net45+sl5+win8+wp8'">     <TargetFrameworkIdentifier>.NETPortable</TargetFrameworkIdentifier>     <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>     <TargetFrameworkProfile>Profile158</TargetFrameworkProfile>     <DefineConstants>$(DefineConstants);PORTABLE158</DefineConstants>   </PropertyGroup>    <ItemGroup Condition="'$(TargetFramework)'=='netstandard1.5'">     <PackageReference Include="Microsoft.CSharp" Version="4.3.0" />     <PackageReference Include="System.ComponentModel" Version="4.3.0" />   </ItemGroup>    <ItemGroup Condition="'$(TargetFramework)'=='net40'">     <Reference Include="Microsoft.CSharp" />   </ItemGroup>    <ItemGroup Condition="'$(TargetFramework)'=='portable40-net45+sl5+win8+wp8'">     <Reference Include="Microsoft.CSharp" />     <Reference Include="System" />     <Reference Include="System.Core" />     <Reference Include="System.Windows" />   </ItemGroup> </Project>