Create Xamarin iOS app from Xamarin Android code

We have a working version of a messaging application developed in Xamarin Android. The current application has the vast majority of the business logic and server interactions encapsulated on classes. The Android specific calls (other than in the controller classes) is contained in a [login to view URL] class. What we need is to take this code base and create a tabbed iOS application using Xamarin for iOS. It must use autosizing and conform to iPhone as well as iPad screen sizes. It only needs to support portrait mode. Attached is a Word document describing the existing functionality along with screen shots of all activities and fragments in the Android application. The developer will have full access to the Android Xamarin project. I have included relevant code files of the "Current Conversations" screen so it will be apparent how the code has been encapsulated. Basically, the UI needs to be developed and the Controller classes created to manipulate the UI by using the existing Model objects