Why would you choose Xamarin Forms over React Native in a company with a .NET stack?

Xamarin Forms allows reusing the existing team's C# and .NET knowledge without adopting JavaScript or the npm ecosystem. Integration with Azure, Azure Active Directory, and other Microsoft services is more natural and compilation to native code offers better performance than WebView solutions.

What is the difference between Xamarin Forms and Xamarin native?

Xamarin Forms shares the user interface between platforms through abstract controls that render as native components on each platform. Xamarin native shares business logic in C# but defines the UI specifically for each platform with native iOS and Android components, offering greater control but less reuse.

What is the MVVM pattern in Xamarin Forms and why is it the recommended pattern?

MVVM separates the View in XAML from the ViewModel with presentation logic and the Model with data. Xamarin's data binding connects the View with the ViewModel without code-behind code, making the code more testable, maintainable, and reusable. It is the recommended pattern because it facilitates unit testing of the ViewModel without depending on the UI.

What advantage does XAML offer over defining UI in C# code in Xamarin Forms?

XAML is more readable for defining UI hierarchies, allows separating visual structure from logic in code-behind, and is compatible with visual designers. Data binding is expressed more clearly in XAML and non-technical designers can understand and modify the structure without knowing C#.

How does Xamarin Forms access platform-specific native APIs?

Through DependencyService which allows defining an interface in shared code and implementing it in each platform project with the Dependency attribute. The shared code calls the interface and Xamarin resolves the correct implementation for iOS or Android at runtime.

What is the current state of Xamarin Forms and what does it mean for new projects?

Xamarin Forms is in maintenance mode with .NET MAUI as its official successor. Microsoft recommends MAUI for new projects. For organizations with existing Xamarin Forms projects, migration to MAUI is the recommended path, although Xamarin Forms support continues until May 2024.

What is Shell in Xamarin Forms and what problem does it solve?

Shell provides a simplified navigation structure for applications with flyout menu, tabs, and page stack configured in a single XAML file. It simplifies the navigation architecture of complex applications without manually managing NavigationPage, TabbedPage, and FlyoutPage separately.

For what type of projects does Xamarin Forms have a clear advantage over other mobile options?

In companies with established .NET teams that need mobile applications integrated with Microsoft systems, in projects with security requirements that favor the Microsoft ecosystem, or in organizations where reusing C# knowledge and Azure Active Directory integration are determining factors.

How would you implement bidirectional data binding in Xamarin Forms with MVVM?

By binding ViewModel properties with Mode=TwoWay in XAML and ensuring the ViewModel implements INotifyPropertyChanged notifying changes with OnPropertyChanged. The page's BindingContext is set to the ViewModel and the framework manages automatic synchronization between the UI and the ViewModel.

What is the difference between Commands and event handlers in Xamarin Forms?

Commands implement ICommand and are bound to actions in XAML with Command binding, keeping logic in the ViewModel and facilitating unit testing. Event handlers in code-behind couple logic to the View and are harder to test. Commands are the recommended practice in MVVM.

How would you manage navigation between pages in Xamarin Forms with MVVM?

Using a navigation service injected into ViewModels that abstracts Xamarin's NavigationPage, allowing navigation from the ViewModel without direct references to the View. Frameworks like Prism or MvvmCross provide these navigation services already implemented with support for parameter passing between pages.

How would you implement custom renderers in Xamarin Forms?

By creating a class that inherits from the corresponding native renderer in each platform project and decorating it with ExportRenderer. This allows customizing the visual or behavioral behavior of a Xamarin control beyond what standard properties allow, directly accessing the underlying native control.

How would you manage the lifecycle of a Xamarin Forms application?

By overriding the OnStart, OnSleep, and OnResume methods in the App class to manage application state when starting, going to the background, and returning to the foreground. For individual page lifecycle, OnAppearing and OnDisappearing are used which execute when navigating to or away from the page.

How would you implement authentication with Azure Active Directory in Xamarin Forms?

Using the MSAL library for Xamarin that manages the OAuth2 flow with Azure AD. The MSAL client is configured with the ClientId and Tenant, AcquireTokenInteractive is called for initial authentication with the system UI, and AcquireTokenSilent for renewing tokens without user interaction, storing the token in the MSAL cache.

What is the difference between CollectionView and ListView in Xamarin Forms?

CollectionView is the modern implementation that replaces ListView with better performance, support for grid and horizontal layouts, multiple selection, and without mandatory separators. ListView has greater compatibility with older versions but CollectionView is the recommended option for new projects due to its greater flexibility and performance.

How would you implement local storage in a Xamarin Forms application?

Using Xamarin Essentials Preferences for simple key-value data, SQLite with sqlite-net-pcl for structured data with queries, or Akavache for object caching with persistence. The choice depends on data complexity, search requirements, and whether synchronization with a backend is needed.

How would you structure a large Xamarin Forms application with multiple modules?

Using Prism as the MVVM framework that provides dependency injection, ViewModel-based navigation, dynamically loadable modules, and decoupled event management. The application is divided into independent module projects that register in the Prism container, facilitating parallel development by different teams.

How would you approach migrating a Xamarin Forms project to .NET MAUI?

Using Microsoft's upgrade assistant that automates much of the changes in project files and namespace references, migrating from Renderers to Handlers which is MAUI's new model, updating NuGet dependencies to MAUI-compatible versions, and verifying behavior on each platform after migration.

How would you optimize scroll performance in complex lists with Xamarin Forms?

Using CollectionView with RecycleElement strategy to reuse cells, implementing lazy image loading with FFImageLoading, reducing cell visual complexity by minimizing nested layouts, using BindableLayout only for small lists, and considering virtualization with DataVirtualization for very large datasets.

How would you implement automated UI tests in a Xamarin Forms application?

Using Appium with the Xamarin.UITest driver that allows interacting with native controls by AutomationId on iOS and Android. Tests are written in C# and run on real devices or emulators in services like App Center Test or BrowserStack, verifying critical user flows in an automated manner.

How would you design the architecture of a Xamarin Forms application with offline mode requirements?

By implementing a repository layer that abstracts the data source, using SQLite as the local store, differential synchronization with the server when connectivity is available, sync conflict management with a last-write-wins or merge strategy depending on the domain, and Xamarin Essentials Connectivity API to detect network changes.

When does it make sense to maintain a Xamarin Forms project instead of migrating to MAUI?

When the project is in maintenance phase with a low rate of changes and migration doesn't provide immediate business value, when there are critical dependencies on Xamarin plugins without a MAUI equivalent yet, or when the team is in the process of gradually adopting .NET MAUI starting with new projects.

Not knowing the transition toward .NET MAUI

Not knowing that Xamarin Forms is in the process of deprecation and that MAUI is its official successor reflects a lack of ecosystem follow-up. In current interviews, knowledge of the framework's state and implications for new and existing projects is expected.

Not implementing MVVM correctly with INotifyPropertyChanged

Putting business logic in the code-behind of XAML pages instead of the ViewModel reflects not understanding the MVVM pattern that is fundamental in Xamarin Forms. It is one of the most frequent and visible anti-patterns in code reviews.

Not using Commands for UI actions

Using event handlers in code-behind instead of Commands bound to the ViewModel couples logic to the View and makes testing difficult. In interviews, knowledge of ICommand and RelayCommand as part of the MVVM pattern in Xamarin Forms is expected.

Not knowing DependencyService for native API access

Not knowing how to access platform-specific functionalities from shared code reflects limited experience developing Xamarin Forms applications with requirements beyond basic UI.

Not evaluating MAUI for new projects

Proposing Xamarin Forms for a new project without evaluating .NET MAUI reflects being out of date. Knowledge that MAUI is the recommended option for new projects and being able to articulate when starting with Xamarin Forms still makes sense is expected.

Not knowing CollectionView as a replacement for ListView

Using ListView for new list implementations without knowing CollectionView reflects not following current Xamarin Forms recommendations. CollectionView is more efficient and flexible and is the recommended practice in current versions.

Xamarin Forms

The .NET framework for cross-platform mobile applications

Xamarin Forms is a Microsoft framework for building cross-platform mobile applications for iOS and Android using C# and .NET with a shared user interface. It allows .NET developers to build native applications with a single codebase in C#, accessing device APIs and compiling to native code for each platform. It is currently being replaced by .NET MAUI as its official successor.

C#.NETXAMLMobile

Market demand

Xamarin Forms has stable demand especially in companies with .NET teams that need mobile presence without adopting new technologies. With the transition toward .NET MAUI, new projects tend to use MAUI, but maintaining existing Xamarin projects continues to generate market demand.

Demand in maintenance of existing projectsHigh adoption in .NET ecosystemActive transition toward .NET MAUI

Technical requirements

Intermediate

Requires mastery of C#, object-oriented programming, and familiarity with the .NET ecosystem. Knowledge of XAML for defining user interfaces and understanding of the MVVM pattern is essential for well-structured Xamarin Forms projects.

Use cases

Real Projects

Xamarin Forms is used to develop:

Enterprise mobile applications in .NET ecosystems
Internal productivity apps for employees
Field applications with device API access
Mobile systems integrated with .NET backends or Azure

Types of Company

Xamarin Forms is adopted by:

Companies with .NET teams that need mobile applications
Organizations in the Microsoft ecosystem with Azure stack
Companies migrating WPF or WinForms applications to mobile
Companies with ERP or CRM systems that need a mobile client

Production Scenarios

Xamarin Forms is widely used in production environments such as:

Applications with Azure AD authentication and MSAL
Apps with camera, GPS, and device sensor access
Applications with offline mode and synchronization with .NET backend
Systems with deep integration with Microsoft services like Office 365

Scalability

Xamarin Forms offers multiple mechanisms to scale applications:

Shell for structured navigation in complex applications
DependencyService for platform-specific native functionality access
MessagingCenter for decoupled communication between components
Lazy loading of pages to optimize startup time

Advantages and Disadvantages

Advantages

Reuse of C# and .NET knowledge for mobile development without new languages.

Natural integration with the Microsoft ecosystem including Azure and Active Directory.

Compilation to native code that offers better performance than WebView solutions.

Disadvantages

In the process of deprecation with .NET MAUI as the recommended successor for new projects.

Learning curve in XAML and in behavior differences between platforms.

Smaller community than React Native or Flutter with fewer available resources.

Comparison

Advantages of .NET MAUI

Official successor with long-term Microsoft support
Additional support for Windows and macOS beyond mobile
Improved architecture with better performance and tooling

Considerations

MAUI is the direct successor to Xamarin Forms with the same philosophy but modernized architecture. For new projects, MAUI is the recommended option. Xamarin Forms remains relevant for maintaining existing projects.