What is Xamarin

A powerful tool for building cross-platform mobile apps using C#.

Download Xamarin from http://xamarin.com/download

Launch Xamarin Studio and select Android -> Android Application for developing Android Apps

Launch Xamarin Studio and select IOS -> iPhone > Single View or Tabbed Application for developing IOS Apps.

ASP.NET WEB API 2

ASP.NET Web API is framework for building RESTful applications on the .NET Framework.

In Web API, a controller is an object that handles HTTP requests when you are creating MVC based applications.

Some of the features are

Attribute Routing, OData, etc..

How to Develop a Cross platform mobile application

We can develop cross platform Mobile Apps using PhoneGap and It is platform dependent

Download it from phonegap.com

Record Audio in Android

Use MediaRecorder class 

start() - used to start recording

stop()- used to stop recording