如何将数据传递给 csproj，或者我可以在 C# .netFramework 项目中的新构建配置上使用#if 指令

Question

I want to create conditional compilation of a .NET framework web forms project because I want to have to build the project in two different ways. I wanted to create something like this:

#if X
    Console.WriteLine("executeCodeX");
#else
    Console.WriteLine("executeCodeY");
#endif

where X should be defined in the msbuild file as a property so I can have the option to build as X or build as Y. I thought of the following two solutions: 1) create a new build configuration for example buildX, and in msbuild call the msbuild command using buildX configration. The problem with this solution is that I don't know how inside of my code I can know what configuration I'm executing with (I can't define the #if X, since X is not recognized).

2) create a property in the msbuild and pass it to the csproj in some way, but yet again, I don't know how to access this property inside of my code in order to tell if I'm executing in X or not.

what is the right approach for the solution?

Answer 1

You need to use the MSBuild property "DefineConstants"
You could set/modify it in a csproj (single project) file or a Directory.Build.props file (whole solution), or just specify it as a command line parameter. It depends exactly how you want things to work.

If you want to specify it in a proj/props file try putting something like this just before the project tag at the end of the project tag:
Using a proxy property makes it easier to add more defined constants, switch what the defaults are, and toggle them on and off separately in the future.

<PropertyGroup>
    <UseX>false</UseX>
    <DefineConstants Condition="'$(UseX)' == 'true'">X;$(DefineConstants)</DefineConstants>
</PropertyGroup>

The <UseX>false</UseX> isn't strictly necessary, but feels slightly more complete.

Then when you want to build it use the following option to build with X off:

msbuild <proj/sln file>  

And with X on:

msbuild <proj/sln file> /p:UseX=true  

Alternatively, the simplest option with little flexibility is to just specify this on the command line:

msbuild <proj/sln file> /p:DefineConstants=X