Architectural guidance for developing Xamarin.Forms enterprise apps that are easier to test, maintain, and evolve. Guidance is provided on how to implement the Model-View-ViewModel (MVVM) pattern, dependency injection, navigation, validation, and configuration management, while maintaining loose coupling.

Mobile app solution

The AppArchitecture mobile app solution organizes the source code and other resources into projects. All of the projects use folders to organize the source code and other resources into categories. The following table outlines the projects that make up the AppArchitecture mobile app:

Project	Description
AppArchitecture	This project is the .NET Standard project that contains the shared code and shared UI.
AppArchitecture.Droid	This project holds Android specific code and is the entry point for the Android app.
AppArchitecture.iOS	This project holds iOS specific code and is the entry point for the iOS app.
AppArchitecture.UITests	This project contains UI tests for the AppArchitecture project.
AppArchitecture.NUnitTests	This project contains unit tests for the AppArchitecture project.

The classes from the SampleApp mobile app can be re-used in any Xamarin.Forms app with little or no modification.

AppArchitecture project

The AppArchitecture project contains the following folders:

Folder	Description
Animations	Contains classes that enable animations to be consumed in XAML.
Behaviors	Contains behaviors that are exposed to view classes.
Controls	Contains custom controls used by the app.
Converters	Contains value converters that apply custom logic to a binding.
Effects	Contains effects.
Exceptions	Contains the custom Exceptions.
Extensions	Contains extension methods for classes.
Helpers	Contains helper classes for the app.
Models	Contains the model classes for the app.
Properties	Contains AssemblyInfo.cs, a .NET assembly metadata file.
Services	Contains interfaces and classes that implement services that are provided to the app.
Triggers	Contains triggers, which are used to invoke an animation in XAML.
Validations	Contains classes involved in validating data input.
ViewModels	Contains the application logic that's exposed to pages.
Views	Contains the pages for the app.

Platform projects

The platform projects contain effect implementations, custom renderer implementations, and other platform-specific resources.

Dependency injection

Dependency injection is a specialized version of the Inversion of Control (IoC) pattern, where the concern being inverted is the process of obtaining the required dependency. With dependency injection, another class is responsible for injecting dependencies into an object at runtime. The following code example shows how the ProfileViewModel class is structured when using dependency injection:

public class ProfileViewModel : ViewModelBase 
{
   private IOrderService _orderService;
   public ProfileViewModel(IOrderService orderService)
{
       _orderService = orderService;
}
... }

The ProfileViewModel constructor receives an IOrderService instance as an argument, injected by another class. The only dependency in the ProfileViewModel class is on the interface type. Therefore, the ProfileViewModel class doesn't have any knowledge of the class that's responsible for instantiating the IOrderService object. The class that's responsible for instantiating the IOrderService object, and inserting it into the ProfileViewModel class, is known as the dependency injection container.

Dependency injection containers reduce the coupling between objects by providing a facility to instantiate class instances and manage their lifetime based on the configuration of the container. During the objects creation, the container injects any dependencies that the object requires into it. If those dependencies have not yet been created, the container creates and resolves their dependencies first.