Fun with value converters

CreditCardNumberValueConverter.cs

public class CreditCardNumberValueConverter : MvxValueConverter
{
  public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
  {
    var builder = new StringBuilder(Regex.Replace(value.ToString(), @"\D", ""));

    foreach (var i in Enumerable.Range(0, builder.Length / 4).Reverse())
      builder.Insert(4*i + 4, " ");

    return builder.ToString().Trim();
  }

  public override object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
  {
    return Regex.Replace(value.ToString(), @"\D", "");
  }
}

PhoneNumberValueConverter.cs

public class PhoneNumberValueConverter : MvxValueConverter
{
  public override object Convert(object value, Type targetType, object parameter, CultureInfo culture)
  {
    var numbers = Regex.Replace(value.ToString(), @"\D", "");

    if (numbers.Length <= 3)
      return numbers;
    if (numbers.Length <= 7)
      return string.Format("{0}-{1}", numbers.Substring(0, 3), numbers.Substring(3));

    return string.Format("({0}) {1}-{2}", numbers.Substring(0, 3), numbers.Substring(3, 3), numbers.Substring(6));
  }

  public override object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
  {
    return Regex.Replace(value.ToString(), @"\D", "");
  }
}