Introducing Xamarin Forms

Today I will introduce the basics of Xamarin.Forms as an alternative to creating user interfaces for mobile devices using C# language and the .NET Framework.

The Xamarin.Forms launched in 2014, and it's a platform that runs on Xamarin and was originally created as a kit of UI tools that allows developers to easily create user interfaces that can be shared across Android, iOS and Windows Phone.

Xamarin.Forms was written in the C# language, and allows for quick prototyping of applications that can evolve over time to complex applications. As Xamarin.Form applications are native apps, they do not have the limitations of other toolkits.

The applications written using Xamarin.Forms are able to use any of the features of the API or the underlying platform, such as CoreMotion, PassKit and StoreKit on iOS; NFC and Google Play on Android; Tiles and Windows Phone. It also means that you can create applications that have parts of your user interface created with Xamarin.Forms while other parts are created using the native UI toolkit.

The Xamarin.Forms applications are architected in the same way as the traditional multiplatform applications with the most common approach is to use Portable Libraries or Shared Projects and then create applications for specific platforms that will consume shared code.

There are two techniques to create user interfaces (UI) in Xamarin.Forms:

1. Create UI in source code using the API provided by Xamarin.Forms,
2. Using XAML (Extensible Application Markup Language), which is Microsoft's declarative markup language that is used to describe interfaces. The user's interface is defined in an XAML file using the XAML syntax, while the runtime behavior is defined in a code-behind file separately;

The advantage to reach multiple platforms with a single programming language is the ability to share code between applications. Before the code can be shared an application must be structured for this purpose and the pattern MVVM architecture helps the developer to separate the code for a view of a specific platform, the code that needs to interact with the platform's API and the Model and View-Model independent platform.

Part of the application which is platform independent and can be isolated in a context of Visual Studio or Xamarin Studio can be placed in a separate project as follows:

1. Shared Asset Project (SAP): that is simply code files and other available assets from other projects;
2. Portable Class Library (PCL): which includes all common code in a dynamic link library (DLL) and then can be referenced from other projects;