Xamarin offers cross-platform development and code-sharing, native performance, and forms for UI building, among other features, in a C# mobile application development platform (MADP).

The debate about what's the best way to create applications for mobile devices remains unsettled between whether to use HTML to create apps that work across both server and mobile platforms or to build apps natively to the mobile platforms for better performance (or to use a hybrid approach). The answer truly lies in what's best for each enterprise. However, if a company has already resolved this argument in favor of building apps native to the mobile hardware in use, there are many options from which to choose for selecting an MADP.

If you take the time to peruse computer publication articles that offer summaries of the top x number of "best" native application development tools for mobile devices, you'll find Microsoft-owned Xamarin listed in a plurality of them. Part of the reason is the wide range of features available with this MADP, which can deliver native Android, iOS, Mac, and Windows apps. Because Xamarin produces native apps for mobile devices, performance of those apps tends to be better because the apps can use hardware-specific acceleration, which is generally superior to apps that have to interpret code at runtime. Running natively, Xamarin apps also can use all functions of platforms and devices, including specific features such as iBeacons and Android Fragments.

The August 2016 version of a Gartner Report, "Critical Capabilities for Mobile Application Development Platforms," also rated Xamarin third (at just .03 points behind the leader) for "B2C Transactional Use Case," which Gartner defines as "business-to-consumer transactions including commerce and banking apps." The report also said Microsoft's offering scored well for "business-to-employee complex" apps, which Gartner classifies as including "multiple-workflow, transactional apps" based on "its cross-platform, native app development capabilities and life cycle management support."

Xamarin is actually a platform solution consisting of Xamarin.Android, Xamarin.iOS, Xamarin.Mac, Xamarin Test Cloud, and HockeyApp. The first three tools focus on their eponymous OSes. Test Cloud automates app and user-interface (UI) testing on more than 2,000 devices, and HockeyApp provides versions for each supported OS that collects crash reports, administers beta version distributions, and analyzes application testing coverage. Together, these solutions let developers write apps in C# and manage those apps throughout each app's total lifecycle. The Visual Studio and Xamarin Mobile Lifecycle Solution package option also includes MVS, Visual Studio Team Services (servicesthat helpteamsto share code, track work, and ship software), Microsoft Azure (a cloud computing platform), and Xamarin University (live classes from mobile development experts).

Originally an independent company, Xamarin was acquired last February by Microsoft, which recently announced it would open-source the Xamarin SDK. Xamarin is already integrated with Microsoft Visual Studio (MVS), the interactive development environment for the Microsoft .NET Framework, and supports Microsoft Portable Class Libraries and most C# 5.0 features. Xamarin has also produced add-ins to MVS that let programmers access code completion and IntelliSense features, the latter enabling lookups of types, methods, and API functions simply by keystroking them.

A Single, Shared Code Base

One of the Xamarin platform's major usability features is the fact that it lets developers deliver mobile apps for all supported platforms using a single C# code base. This means code blocks, APIs, and data structures can be between 70 and 90 percent (or more) reusable across the supported mobile platforms.

A Xamarin.Forms feature, now part of MVS, lets developers build UI parts that are sharable across mobile platforms. This utility lets app pages incorporate advanced gesture support and layouts, buttons, labels, lists, and other common controls. At runtime, each page and its controls are mapped to platform-specific native UI elements. The Forms feature uses Microsoft Extensible Application Markup Language (XAML) and also lets developers build UI elements or themes directly using that language or C#. Included is a previewer feature that lets developers see screen layouts directly from XAML source code within the IDE. In addition, Forms lets developers deep-link Forms pages with web, email, and other external sources from directly within the mobile app. Finally, programmers can extend Forms with custom controls that enable definition of layouts, pages, cells, and new controls, as well as customize the behavior of subclass-included controls.

Developers can also use either MVS, Xamarin Studio, or XAML to build user interfaces that include basic animations, two-way data bindings that automatically synchronize data between controls and models, dependency injections with under 10ms startup times, and centers for loosely coupled messaging between application components.

Code-Sharing Mechanisms

Xamarin's Shared Projects feature (sometimes called Shared Asset Projects) lets developers make any file part of a code base that can be shared among all supported mobile platforms. Compiler directives let application designers conditionally designate platform-specific code to be included for compiling with any subset of apps residing in the Shared Projects repository. Directives can include instructions to enable or disable code sections, varying with which app is using the code. Xamarin also includes IDE support for managing compiler directives and that enable developers to view what code will look like in each application.

Under .NET, different platforms use different subsets of the .NET Base Class Library (BCL), so each platform profile can only use class libraries tailored to that platform. Xamarin overcomes this problem in two ways. The Shared Projects feature uses conditional compiler instructions to differentiate between code paths so developers can still use a single set of code files.

The second way is using Portable Class Libraries (PCL). These libraries can be standard ones like SQLite or Json.NET, or a custom PCL built by the developer. During the PCL creation process, the developer is guided through parameter questions that establish a "profile" identifier that describes which mobile platforms the library will support. This creation process enables centralized code sharing, lets refactoring operations affect all code in a given PCL or shared project, and supports referencing of the output assembly by other developers and projects.

Securing Xamarin Apps

Securing data and communications for mobile apps is obviously a high priority. One method of enabling security is via Microsoft's Active Directory (AD) authentication, which protects AD implementations on user systems and in Azure AD-hosted directories. Another method is that Xamarin apps can use security inherent to the mobile device OSes, such as the App Transport Security and Security Namespace features of iOS. Finally, apps can gain additional security via the Xamarin Component Store, a collection of downloadable components for each supported mobile platform that offer such services as database encryption using 256-bit AES, SSL/TLS encryption for every major Internet protocol, and SSH 2.0 encryption.

Additional Functions and Planned Enhancements

The store also provides additional components that provide functions as varied as user authentication, credit-card and electronic-check processing, signature-pad support, barcode scanning, device-connection status, Facebook interfaces, and additional software development kits for all supported platforms, among many other options. Some components are freeware, and others are available for varying fees.

Microsoft also offers NuGet, a gallery of more than 64,000 open-sourced software components available under an Apache 2 license.

Currently in beta and scheduled for year-end release is Microsoft PowerApps, categorized by Gartner as a Rapid Mobile App Development (RMAD) tool, which is supposed to produce single-platform mobile apps more quickly than traditional methods, produced apps embodying both front-end development and back-end integration. PowerApps is compatible with Xamarin and will support integration with Microsoft Office applications. PowerApps also can use the Representational State Transfer (REST) architecture, favored for cloud-based APIs, to build web and hybrid apps for mobile devices using Apache Cordova, which lets developers create mobile apps in CSS3, HTML5, and JavaScript rather than depend on APIs designed for individual mobile platforms.

With a large company backing it, flexible features, and huge libraries of established additional functions, Xamarin is worth a look if you're committed to a native-app mobile-device strategy.

John Ghrist

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John Ghrist has been a journalist, programmer, and systems manager in the computer industry since 1982. He has covered the market for IBM i servers and their predecessor platforms for more than a quarter century and has attended more than 25 COMMON conferences. A former editor-in-chief with Defense Computing and a senior editor with SystemiNEWS, John has written and edited hundreds of articles and blogs for more than a dozen print and electronic publications. You can reach him at ghrist@comcast.net.