BindRadioButton

////////// Usage ///////////

this.BindRadioButtons(v => v.ViewModel.RadioButtonValue, 
                      v => v.RadioButtonA, "A",
                      v => v.RadioButtonB, "B");

////////// Implementation ///////////

public static IDisposable BindRadioButtons<TSender, TViewModelValue>(this TSender view,
                                                                     Expression<Func<TSender, TViewModelValue>> viewModelProperty,
                                                                     Expression<Func<TSender, RadioButton>> button0,
                                                                     TViewModelValue value0, 
                                                                     Expression<Func<TSender, RadioButton>> button1,
                                                                     TViewModelValue value1)
{
    var d0 = view.BindRadioButton(viewModelProperty, button0, value0);
    var d1 = view.BindRadioButton(viewModelProperty, button1, value1);
    
    return new CompositeDisposable(d0, d1);
}

private static IDisposable BindRadioButton<TSender, TViewModelValue>(this TSender view,
                                                             Expression<Func<TSender, TViewModelValue>> viewModelProperty,
                                                             Expression<Func<TSender, RadioButton>> button,
                                                             TViewModelValue value)
{
    var isCheckedProperty = typeof(RadioButton).GetProperty("IsChecked", BindingFlags.Instance | BindingFlags.Public);
    var isCheckedAccess = Expression.MakeMemberAccess(button.Body, isCheckedProperty);
    var isCheckedLambda = Expression.Lambda<Func<TSender, bool?>>(isCheckedAccess, new[] { Expression.Parameter(typeof(TSender), "v") });
    
    var fromViewToViewModel = view.WhenAnyValue(isCheckedLambda)
                                  .Where(check => check.HasValue && check.Value)
                                  .Select(_ => value)
                                  .BindTo(view, viewModelProperty);
    
    var fromViewModelToView = view.WhenAnyValue(viewModelProperty)
                                  .Select(val => val.Equals(value))
                                  .BindTo(view, isCheckedLambda);

    return new CompositeDisposable(fromViewModelToView, fromViewToViewModel);
}