Xamarin iOS allows you to consume a third-party Objective-C library. Before you had to use Xamarin.iOS's Binding Projects to create a C# binding to the native Objective-C libraries. Inside this Binding project you’ll find two files: ApiDefinition.cs and StructsAndEnums.cs.
The ApiDefinition.cs is where you will define the API contract, this is the file that describes how the underlying Objective-C API is projected into C#. The StructsAndEnums.cs file is the file where you will enter any definitions that are required by the interfaces and delegates.
To bind your library you will have to create C# interfaces and annotate these interfaces with attributes to map the C# interface to the corresponding Objective-C class. Although it’s not too hard to do this, expect a lot of work for a moderate size Objective-C library.
To make this job easier, Xamarin introduced a new tool: Objective Sharpie, a very powerful binding definition generator for third party Objective C libraries to help provide APIs matching the .NET idioms.
“Objective Sharpie takes much of the manual work of translating Objective C APIs into binding definitions that are consumed by Xamarin’s binding tools. Download your third party library, point Objective Sharpie to its header files, and off you go.”