Conditional compilation symbol for a .NET Core class library

Question

I have created a .NET Core R2 class library and have some common code that I use for several different platforms.

Some of the code is not valid in the .NET Core platform and so I wish to wrap it around a conditional compilation symbol. I first searched the Internet to see if I could find a built-in symbol (like SILVERLIGHT for Silverlight applications and WINFX_CORE for Windows 8 applications), but I was not able to find any information, so I decided to create my own symbol. This also does not seem to work.

From everything I read, adding and using a symbol should be easy. Just add a value to the conditional compilation symbols in the project properties → Build tab. I did that, but it does not seem to work. Here are a couple of screenshots...

Notice that I added a NET_CORE value in the conditional compilation symbol, but when I use it in code the code is not being ignored.

1. Is there is a built-in symbol for the .NET Core platform (I am using R2)?

2. If there is not one, what am I doing wrong creating my own symbol?

The .xproj file:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="14.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <VisualStudioVersion Condition="'$(VisualStudioVersion)' == ''">14.0</VisualStudioVersion>
    <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>
  </PropertyGroup>
  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.Props" Condition="'$(VSToolsPath)' != ''" />
  <PropertyGroup Label="Globals">
    <ProjectGuid>253184d7-9b42-4233-a871-8cfa3ee9e83e</ProjectGuid>
    <RootNamespace>Linq2Db.NetCore</RootNamespace>
    <BaseIntermediateOutputPath Condition="'$(BaseIntermediateOutputPath)'=='' ">.\obj</BaseIntermediateOutputPath>
    <OutputPath Condition="'$(OutputPath)'=='' ">.\bin\</OutputPath>
    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
    <SccProjectName>SAK</SccProjectName>
    <SccProvider>SAK</SccProvider>
    <SccAuxPath>SAK</SccAuxPath>
    <SccLocalPath>SAK</SccLocalPath>
  </PropertyGroup>
  <PropertyGroup>
    <SchemaVersion>2.0</SchemaVersion>
  </PropertyGroup>
  <Import Project="$(VSToolsPath)\DotNet\Microsoft.DotNet.targets" Condition="'$(VSToolsPath)' != ''" />
</Project>

---

UPDATE: I was able to resolve this using the link in the provided answer. Here are the details...

Originally the project.json file looked like this...

{
  "dependencies": {
        "NETStandard.Library": "1.5.0-rc2-24027"
  },
  "frameworks": {
    "netstandard1.5": {
      "imports": "dnxcore50"
    }
  },
  "buildOptions": {
    "defines": [ "NET_CORE" ]
  }
}

I resolved the issue by changing it to this...

{
  "frameworks": {
    "netstandard1.5": {
      "imports": "dnxcore50",
      "dependencies": {
        "NETStandard.Library": "1.5.0-rc2-24027"
      },
      "buildOptions": {
        "define": [ "NET_CORE" ]
      }
    }
  }
}

Answer 1

Since xproj was discontinued, here is how it is done in the new Visual Studio 2017 .csproj files.

<PropertyGroup Condition="'$(TargetFramework)' == 'netstandard1.3' Or '$(TargetFramework)' == 'netstandard1.6' ">
    <DefineConstants>NET_CORE</DefineConstants>
</PropertyGroup>

Then instead of:

private TypeInfo GetTypeInfo(Type type)
{
    #if NETSTANDARD1_3 || NETSTANDARD1_6
        // Core
    #else
        // Full framework
    #endif
}

You can do:

private TypeInfo GetTypeInfo(Type type)
{
    #if NET_CORE
        // Core
    #else
        // Fullframework
    #endif
}

See here for more details on multi-targeting: Developing Libraries with Cross Platform Tools, How to Multitarget

Answer 2

Conditional variables should be defined in your project.json file for RC2, and I have a sample project here,

Port #SNMP from .NET Core RC1 to RC2

But there are also predefined ones from this article,

Developing Libraries with Cross Platform Tools

Answer 3

There is a bug in the .NET Core xproj project type. When you define a conditional compilation symbol through the project settings, it defines the element as "defines", but this is incorrect. It should create an element called "define". You can work around the issue by editing the project.json manually.

I have logged this bug with Microsoft in two places. Please take the time to register your annoyance with Microsoft so that they eventually get around to fixing it and not causing this grief for others.

This thread has a detailed explanation of the problem with steps to repro, and screenshots: https://github.com/dotnet/cli/issues/4022#issuecomment-238777946

This is the Microsoft Connect bug report: https://connect.microsoft.com/VisualStudio/feedbackdetail/view/2983351/conditional-compilation-symbols-broken-in-net-core-projects#tabs