INTRODUCTION 

Xamarin is a Microsoft-owned San Francisco, California based software company founded in May 2013 by the engineers that created Mono,Mono for Android and MonoTouch that are cross-platform implementations of the Common Language Infrastructure (CLI) and Common Language Specifications (often called Microsoft .NET).

With a C#-shared codebase, developers can use Xamarin tools to write native Android, iOS, and Windows apps with native user interfaces and share code across multiple platforms. Over 1 million developers use Xamarin's products in more than 120 countries around the world as of May 2015.building our first Xamarin.Android application.

Overview

The phrase "write-once, run everywhere” is often used to extol the virtues of a single codebase that runs unmodified on multiple platforms. Xamarin is not just a "write-once, run everywhere” platform, because one of its strengths is the ability to implement native user interfaces specifically for each platform. However, with thoughtful design it’s still possible to share most of the non-user interface code and get the best of both worlds: write your data storage and business logic code once, and present native UIs on each platform. 

key points

• Use C# - Write your apps in C#. Existing code written in C# can be ported to iOS and Android using Xamarin very easily, and obviously used on Windows Phone.

• Utilize the MVC design pattern - Develop your application’s User Interface using the Model/View/Controller pattern.

• Build native UIs - Each OS-specific application provides a different user-interface layer (implemented in C# with the assistance of native UI design tools)

By following the principle of separation of responsibility by layering your application architecture and then moving core functionality that is platform agnostic into a reusable core library, you can maximize code sharing across platforms, as the figure below illustrates:

Installation instructions for Xamarin.Android on Mac and Windows.next