.NET: Different target frameworks via project configuration

Question

I would like to have two different .net framework targets via configuration in Visual Studio 2015. While for references, you can edit the CSPROJ file and add a conditions, this does not seem to work for the TargetFrameworkVersion in the first PropertyGroup of the file. I have the impression that any Condition in that element causes VS to completely ignore this element and to fall back to the default value of "v4.0".

Is there any way I can get different target framework versions for different configurations?

This is what I tried in the CSPROJ file:

<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    ...
    <!-- this is what VS2015 would put into the file:
    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
    -->
    <!-- this is what does not work: -->
    <TargetFrameworkVersion Condition="'$(Configuration)' == 'OLD_Debug' OR '$(Configuration)' == 'OLD_Release'">v3.5</TargetFrameworkVersion>
    <TargetFrameworkVersion Condition="'$(Configuration)' == 'NEW_Debug' OR '$(Configuration)' == 'NEW_Release'">v4.0</TargetFrameworkVersion>
    ...
  </PropertyGroup>
  ...
</Project>

A similar approach with conditions for the assembly references works fine.

EDIT I found a similar Stackoverflow question: Targetting multiple .net framework versions by using different project configurations and tried the approach suggested in the non-accepted answer to remove the TargetFrameworkVersion from the first PropertyGroup block, and edit the later <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'OLD_Debug|AnyCPU' "> blocks to contain it, but my assembly is still compiled for framework 3.5 no matter which configuration I use. At least if I look at the assembly from Powershell using [System.Reflection.Assembly]::LoadFrom("C:\\PATH\\MyAssembly.dll").ImageRuntimeVersion , I always get version 2, not 4.

Answer 1

The approach found in this answer to a similar question works: Keep the first PropertyGroup without configuration specific settings, remove the TargetFrameworkVersion element from it. And add the TargetFrameworkVersion settings to the configuration specific PropertyGroup s which are in the file anyway, just double them for debug/release:

<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    ...
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'OLD_Debug|AnyCPU' ">
    ...
    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'OLD_Release|AnyCPU' ">
    ...
    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'NEW_Debug|AnyCPU' ">
    ...
    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'NEW_Release|AnyCPU' ">
    ...
    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
  </PropertyGroup>
  ...
</Project>

I verified this as follows:

1. My assembly references version 2.0.0.0 of the mscorlib assembly for the 3.5 framework ( OLD_... configurations), and version 4.0.0.0 of mscorlib for the 4.0 framework ( NEW_... configurations).

2. Using ILSpy , I found that the 3.5 version of my assembly has no attribute for the target framework, as this was only introduced since version 4, but the version 4 framework appears as an attribute of the assembly:

    [assembly: TargetFramework(".NETFramework,Version=v4.0", FrameworkDisplayName = ".NET Framework 4")]