Xamarin ReactiveUI and MVVM

Introduction

ReactiveUI is a MVVM library used in Xamarin development, which helps create better and more maintainable mobile applications. ReactiveUI uses the power of Reactive Extensions (Rx) and its operators, which helps achieve composition and efficient handling of user interactions. MVVM stands for Model-View-ViewModel, which is a design pattern used to create complex applications by separating the concerns between the Presentation (View), Data (Model), and Business Logic (ViewModel).

Benefits of ReactiveUI and MVVM

• Clear Separation of Concerns: By separating the logic, you can create well-organized code. Presentation, Data, and Business Logic are independent of each other, and each layer leaves particular responsibilities, thus making it easier to change and maintain.

• Easier to Test: The Model-View-ViewModel pattern and Reactive Extensions makes testing with Xamarin easier while accommodating an array of scenarios. The defined interfaces between each layer provide better testability and transparency.

• Better User Experience (UX): ReactiveUI ensures that user interactions are handled efficiently and smoothly by leveraging Reactive Extensions. Developers can effortlessly incorporate smooth animations and tailored experiences within their app.

MVVM Basics

The following are the three key elements of MVVM:

• Model - Represents the data or model of the application, such as classes, enums, etc. The Model comes with the business logic of the application and does not have any knowledge of the View or ViewModel.

• View - The visual and the interactive part of the application, such as pages, dialogs, buttons, and user controls. The View sends input to the ViewModel and displays the output from it.

• ViewModel - Acts as a mediator between the Model and View. The ViewModel processes user input, retrieves data from the Model, processes it, and makes it available to the View. The ViewModel does not have any knowledge of the View hierarchy, and it emits output data to the View and translates the commands/events from the View to the Model.

ReacticeUI Basics

ReactiveUI is a lightweight library used for MVVM applications in Xamarin development. It combined the concepts of (FRP) Functional Reactive programming and the (MVVM) Model-View-ViewModel patterns. Here are some essential concepts of ReactiveUI:

• Reactive Command - Simplified method to handle complex command events handling. Commands includes classes, which can be executed, able to determine if it is running or not, able to initialize observable subscriptions to other reactiveui objects etc.

• Reactive Observable - A sequence of data that can change over time. The observable sequence can be transformed, filtered, or combined using Reactive Extensions operators, making it more efficient.

• Reactive Binding - Simplified method to handle view binding without manually subscribing for UI elements. This feature allows the UI elements to be automatically updated when the data changes, thus making the code less verbose.

Example

Here is an example of how ReactiveUI and MVVM can be used in Xamarin development.

// Create a model
public class Person
{
   public string Name { get; set; }
   public int Age { get; set; }
}

// Create a ViewModel
public class PersonViewModel : ReactiveObject
{
   private string _name;
   private int _age;

   public PersonViewModel(Person person)
   {
       Person = person;
       _name = person.Name;
       _age = person.Age;
   }

   public Person Person { get; }

   // Bindable property for name
   public string Name
   {
       get => _name;
       set => this.RaiseAndSetIfChanged(ref _name, value);
   }

   // Bindable property for age
   public int Age
   {
       get => _age;
       set => this.RaiseAndSetIfChanged(ref _age, value);
   }
}

// Create a View
public class PersonPage : ContentPage
{
   public PersonPage(PersonViewModel viewModel)
   {
       BindingContext = ViewModel = viewModel;
       // simple page layout
       var nameEntry = new Entry { };
       nameEntry.SetBinding(Entry.TextProperty, nameof(PersonViewModel.Name));
       var ageEntry = new Entry { };
       ageEntry.SetBinding(Entry.TextProperty, nameof(PersonViewModel.Age));

       Content = new StackLayout
       {
           Orientation = StackOrientation.Vertical,
           Children = {
               new Label { Text = "Name" },
               nameEntry,
               new Label { Text = "Age" },
               ageEntry,
           }
       };
   }

   PersonViewModel ViewModel;
}

• A Person class is created to represent our model.
• Next, PersonViewModel is created with Name and Age properties representing bindable properties in the View.
• A PersonPage is created using Xamarin's ContentPage that is binded to the PersonViewModel. The View contains Entry controls that are bound to the View properties.

##Conclusion

Xamarin Forms with MVVM and ReactiveUI is the perfect stack for building scaleable, clean and maintainable mobile applications. By separating the concerns and coupling ReactiveUI with MVVM patterns, we achieve an intuitive UX and optimized architecture, which makes it possible to maintain a large project with ease.