Data Binding in ReactiveUI¶

A binding connects a property on a view model to a property on a view. When one side changes, the binding writes the new value to the other side. ReactiveUI bindings are written with lambda expressions, so a renamed property breaks the build instead of failing at run time.

ReactiveUI.Binding is the binding engine. A source generator reads each binding at build time and writes the code for it, so bindings need no reflection and work with trimming and Native AOT. The Binding section covers:

• Observing property changes with WhenChanged, WhenAnyValue and the other observation methods.
• Bindings with BindOneWay, BindTwoWay, BindTo, BindCommand and BindInteraction.
• Converters and custom converters for values whose types differ.
• Notification mechanisms, views, threading and setup.

Platforms¶

The platform pages below cover the view base classes and activation for each UI framework. Each one builds on WhenActivated and the platform base classes.

• Android

• iOS

• MAUI

• Windows Presentation Foundation

• Windows Forms

• Avalonia UI

Implement IViewFor on the view¶

A view needs an IViewFor<TViewModel> implementation before it can use the view-first binding methods. The way to implement it depends on the platform.

• iOS: change the base class to one of the Reactive UIKit classes, such as ReactiveViewController, and implement ViewModel with RaiseAndSetIfChanged. You can also implement INotifyPropertyChanged on the view and make sure the ViewModel property signals changes.

• Android: change the base class to one of the Reactive Activity or Fragment classes, such as ReactiveActivity<T>. You can also implement IViewFor<T> on the view and make sure the ViewModel property signals changes.

• XAML-based platforms: implement IViewFor<T> by hand and make ViewModel a DependencyProperty. A UserControl can use the ReactiveUserControl<TViewModel> base class instead.