Mvvm.cs

    class MvvmModel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        internal bool _ignoreUpdate = false;

        protected void OnPropertyChanged(string propertyName)
            => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    static class Mvvm
    {
        public static void Bind<TViewModel, TResult>(TViewModel viewModel, Expression<Func<TViewModel, TResult>> expression, UITextField textField)
            where TViewModel : MvvmModel
        {
            var propertyName = (expression.Body as MemberExpression).Member.Name;
            var viewModelType = typeof(TViewModel);
            var viewModelProperty = viewModelType.GetProperty(propertyName);

            viewModel.PropertyChanged += (sender, e) =>
            {
                if (viewModel._ignoreUpdate) { return; }

                if (e.PropertyName == propertyName)
                {
                    textField.Text = viewModelProperty.GetValue(sender, null) as string;
                }
            };

            textField.AddTarget((sender, e) =>
            {
                viewModel._ignoreUpdate = true;
                viewModelProperty.SetValue(viewModel, textField.Text, null);
            }, UIControlEvent.EditingChanged);
        }
    }

Mvvm.Example.cs

    class VenueDetailViewModel : MvvmModel
    {
        string _proprietor;
        public string Proprietor { get { return _proprietor; } set { _proprietor = value; OnPropertyChanged(nameof(Proprietor)); } }
        public string BusinessName { get; set; }
    }