Below is a example of what we did to the ReactiveUI.Avalonia project that we want to do to Extensions project.

We want to put some named TFMs in the Directory.Build.props file, then rely on those for the two projects.

so our target for the libbrari will be netstandard2.0;net462/net472;net8.0;net9.0;net10.0 and for testing it'll be net8.0/net9.0/net10.0/net462/net472 (no netstandard) exclusively. the net framework TFMs are new, yes likely covered by netstandard but doesn't hurt.

separate out the variables for the framework tfms and only compile those on windows platforms

the combine into the final TFMs for the project and testing targets by combining together the propertygroup items together based on the build environment.

Yes this is a bit of a simpler project but it brings it in line with rxui projects in general.

Description:

Currently, the ReactiveUI.Avalonia project hardcodes the Target Frameworks (TFMs) in its .csproj file. We want to refactor this to use the same pattern as splat and ReactiveUI, where TFMs are defined in the Directory.Build.props file for better consistency and easier maintenance across the repositories.

Instructions:

1. Update src/Directory.Build.props:
   In reactiveui/reactiveui.avalonia/ReactiveUI.Avalonia-Add.NET10.0SupportAndMinorAPIImprovements/src/Directory.Build.props, replace the existing <BaseTargetFrameworks> property with a more specific one for Avalonia. This will allow us to manage the TFMs for all projects in this repository from a single location.

   Replace this:

   <BaseTargetFrameworks>netstandard2.0;net8.0;net9.0</BaseTargetFrameworks>

   With this:

   <AvaloniaTargetFrameworks>netstandard2.0;net8.0;net9.0;net10.0</AvaloniaTargetFrameworks>

2. Update src/ReactiveUI.Avalonia/ReactiveUI.Avalonia.csproj:
   In reactiveui/reactiveui.avalonia/ReactiveUI.Avalonia-Add.NET10.0SupportAndMinorAPIImprovements/src/ReactiveUI.Avalonia/ReactiveUI.Avalonia.csproj, modify the <TargetFrameworks> element to reference the new property defined in Directory.Build.props.

   Replace this:

   <TargetFrameworks>netstandard2.0;net8.0;net9.0;net10.0</TargetFrameworks>

   With this:

   <TargetFrameworks>$(AvaloniaTargetFrameworks)</TargetFrameworks>

By making these changes, we will have a more consistent and maintainable build process that aligns with the standards set in our other repositories.

Test projects CANNOT have netstandard, so have a separate target in the directory.build.props file for tests, eg just net8/9/10