UiExtensions.cs

public static class UiExtensions
{
  public static IObservable<Keycode> RxKeyPressed(this EditText tv, bool ignoreBackKey = false) =>
    Observable.Create((IObserver<Keycode> obs) => {
      tv.SetOnKeyListener(new KeyUpPressedListener(obs, ignoreBackKey));
      return () => tv.SetOnKeyListener(null);
    });

  public static IObservable<string> RxTextChanged (this TextView tv, int dueTimeMilliseconds = 500) =>
    FromEventPattern<TextChangedEventArgs> (
      ev => tv.TextChanged += ev,
      ev => tv.TextChanged -= ev
    ).Select(_ => _.EventArgs.Text.ToString())
     .Restrict(dueTimeMilliseconds);
       
  public static IObservable<Unit> RxClick(this View v) =>
    FromEventPattern(
      ev => v.Click += ev,
      ev => v.Click -= ev
    ).Select(_ => Unit.Default);
      
  public static IObservable<int> RxSelectedItem(this Spinner s) =>
    FromEventPattern<AdapterView.ItemSelectedEventArgs>(
      ev => s.ItemSelected += ev,
      ev => s.ItemSelected -= ev
    ).Select(_=> (_.Sender as Spinner).SelectedItemPosition);
}