略作修改StringLengthAttribute：

slightly modified StringLengthAttribute:

public class StringRangeAttribute : ValidationAttribute
{
    // Methods
    public StringRangeAttribute(int minimumLength, int maximumLength)
        : base(() => "The {0} must be between {1} and {2} chars long.")
    {
        MaximumLength = maximumLength;
        MinimumLength = minimumLength;
    }

    public override string FormatErrorMessage(string name)
    {
        return string.Format(CultureInfo.CurrentCulture, ErrorMessageString, new object[] { name, MinimumLength ,MaximumLength });
    }

    public override bool IsValid(object value)
    {
        if (value != null)
        {
            return (((string)value).Length <= MaximumLength) && (((string)value).Length >= MinimumLength);
        }
        return true;
    }

    public int MaximumLength { get; set; }
    public int MinimumLength { get; set; }
}