Xamarin Forms is known as a user interface abstraction library. It operates as a Portable Class Library (PCL), sitting on the target platforms and feeding in the UI elements that the application needs. It is as good as it sounds! Application user interfaces can be quickly constructed as a large amount of any other code can be shared.
Note
The Xamarin Forms library also allows you to access the platform hardware through injection with UI customization, through custom renderers. Both of these topics are covered later in the book.
Being an abstraction layer, only those elements with an analogous element on all of the target platforms are covered. For example, at the time of writing, there is not a single checkbox in forms and graphics on tab pages, for Android gives nothing.
This library is also part of a PCL. The PCL itself only supports a subset of the standard .NET library classes, namely those that are supported on all platforms. This leads to quite a few issues, such...