UI implementations are native to each OS, the C# code is often shared between apps but UI interaction code tends to be per platform. There are some places that

UI implementations are native to each OS, the C# code is often shared between apps but UI interaction code tends to be per platform. There are some places that abstraction layers make sense but part of the value proposition is that you still have a completely native build and native look and feel. Therefore, in these UI cases, you write platform specific code.