ReactiveExample

This is a sample app that shows how to use System.Reactive and ReactiveUI with Terminal.Gui. The app uses the MVVM architecture that may seem familiar to folks coming from WPF, Xamarin Forms, UWP, Avalonia, or Windows Forms. In this app, we implement the data bindings using ReactiveUI WhenAnyValue syntax and ObservableEvents — a Source Generator that turns events into observable wrappers.

Scheduling

In order to use reactive extensions scheduling, copy-paste the TerminalScheduler.cs file into your project, and add the following lines to the composition root of your Terminal.Gui application:

// Configuration (themes, schemes, settings) is applied automatically at assembly load.
using IApplication app = Application.Create ();
app.Init ();
RxApp.MainThreadScheduler = new TerminalScheduler (app);
RxApp.TaskpoolScheduler = TaskPoolScheduler.Default;

LoginView loginView = new (new ());
app.Run (loginView);
loginView.Dispose ();

From now on, you can use .ObserveOn(RxApp.MainThreadScheduler) to return to the main loop from a background thread. This is useful when you have a IObservable<TValue> updated from a background thread, and you wish to update the UI with TValues received from that observable.

Data Bindings

If you wish to implement OneWay data binding, then use the WhenAnyValue ReactiveUI extension method that listens to INotifyPropertyChanged events of the specified property, and converts that events into IObservable<TProperty>:

// 'usernameInput' is 'TextField'
ViewModel
    .WhenAnyValue (x => x.Username)
    .BindTo (usernameInput, x => x.Text);

Note that your view model should implement INotifyPropertyChanged or inherit from a ReactiveObject. If you wish to implement OneWayToSource data binding, listen to the view's change event via Observable.FromEventPattern. For TextField specifically, the generated .Events () wrappers do not work — as of Terminal.Gui 2.5 the ObservableEvents source generator cannot wrap TextField, which hides View.TextChanging with a different delegate type (.Events () remains fine for other views, like the Button below). TextField implements IValue<string>, so its ValueChanged event delivers the new value directly and only fires on real changes:

// 'usernameInput' is 'TextField'
Observable
    .FromEventPattern<ValueChangedEventArgs<string?>> (
        h => usernameInput.ValueChanged += h,
        h => usernameInput.ValueChanged -= h)
    .Select (e => e.EventArgs.NewValue ?? string.Empty)
    .BindTo (ViewModel, x => x.Username);

If you combine OneWay and OneWayToSource data bindings, you get TwoWay data binding. Invoking commands should be as simple as this:

// 'clearButton' is 'Button'
clearButton
    .Events ()
    .Accepting
    .InvokeCommand (ViewModel, x => x.Clear);