How to make UseWindowsForms conditional in csproj?

Question

I have a C# library that I want to publish on Nuget. Currently it only builds if I target net8.0-windows because it has <UseWindowsForms>true</UseWindowsForms>.

However, it uses Windows Forms for only some functionality. I would like to conditionally exclude that functionality with #if directives so that I can still have a version of the library with the rest of the functionality that doesn’t rely on Windows Forms, and have that target net8.0 or netstandard2.0.

Is there a way to make UseWindowsForms conditional in this way?

Timwi · Accepted Answer · 2025-06-09 15:21:12Z

1

I found the answer. You can still multi-target as usual:

<TargetFrameworks>net8.0-windows;net8.0;netstandard2.0</TargetFrameworks>

but then you have to create a separate PropertyGroup element as follows:

<PropertyGroup Condition="'$(TargetFramework)' == 'net8.0-windows'">
  <UseWindowsForms>true</UseWindowsForms>
  <DefineConstants>USE_WINDOWS_FORMS;$(DefineConstants)</DefineConstants>
</PropertyGroup>

This will apply WinForms only when targeting net8.0-windows. It also defines a compile-time constant so that I can exclude the relevant code from the library:

#if USE_WINDOWS_FORMS
    // WinForms-specific methods go here
#endif

answered Jun 9 at 15:21

Timwi

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