Xamarin is a powerful development platform that is revered for its ability to facilitate cross-platform development by sharing a single codebase across multiple operating systems.

Core Components of Xamarin

1. Xamarin.iOS: Formerly known as MonoTouch, this is the iOS component of Xamarin that allows both native and C# development. It boasts native performance and access to thousands of libraries through the NuGet package manager.

2. Xamarin.Android: Often referred to as Mono for Android, this component brings both native and C# development to Android. It provides access to multiple Android devices and allows developers to use Java libraries alongside C# via a binding process.

3. Xamarin.Forms: This unified UI toolkit provides a way to build user interfaces for iOS, Android, and UWP using XAML or code. It allows for around 90% of code sharing across platforms.

4. .NET: Xamarin suites leverage the powerful .NET framework, permitting developers to write code in C#, which is then compiled into native code.

Shared and Platform-Specific Code

Xamarin encourages a code-sharing architecture that allows for both platform-specific and shared code, offering the best combination of reusability and platform-specific optimization.

Code Sharing

• UI (User Interface): With Xamarin.Forms, 100% of the UI code can be shared across platforms, decreasing development time significantly.

• Business Logic: Essential business and application logic are great candidates for sharing across platforms. This includes data models, network operations, and local storage implementations.

• Services: Services such as data access, security, and location can be defined in a shared project, ensuring consistency across platforms.

• View Models: When using the MVVM pattern, most of the View Models can be shared.

Platform-Specific Code

While maximising code sharing is crucial, there are times when it’s necessary to tailor parts of the app to each platform. Xamarin allows for this through:

• Dependency Service: This mechanism enables platform-specific implementations for services or functionality. For instance, if there’s a requirement for platform-specific permissions handling, this can be achieved using the Dependency Service.

• Custom Renderers: Xamarin.Forms permits the customisation of UI views at a platform level.

The NuGet Package Manager

Xamarin relies on the NuGet package manager to offer a plethora of libraries and components. These can range from utilities for backend integrations to UI controls. NuGet keeps these components updated and ensures libraries are easily integrable in the Xamarin projects.