"；非静态字段、方法或属性需要对象引用'；RxCard.dataobjects.Pharmacy.Area

我有一个自定义验证属性，需要将一些属性传递给它。但是，在应用该属性时会出现问题。我在向后学习.net，所以我倾向于陷入"更简单"的问题。我已经尝试过将该房产设为静态，但这打乱了我的部分视图。我该如何处理

属性：

  public class MinimumPhoneDigits : ValidationAttribute
    {
        public string[] _properties;
        public int _expectedsize;
        public MinimumPhoneDigits(int expectedsize, params string[] properties)
        {
            ErrorMessage = "Not the expected size!";
            _properties = properties;
            _expectedsize = expectedsize;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (_properties == null || _properties.Length < 1)
            {
                return new ValidationResult("WOAH! Not the right size.");
            }
            int totalsize = 0;
            foreach (var property in _properties)
            {
                var propinfo = validationContext.ObjectType.GetProperty(property);
                if (propinfo == null)
                    return new ValidationResult(string.Format("could not find {property}"));
                var propvalue = propinfo.GetValue(validationContext.ObjectInstance, null) as string;
                if (propvalue == null)
                    return new ValidationResult(string.Format("wrong property for {property}"));
                totalsize += propvalue.Length;
            }
            if (totalsize != _expectedsize)
                return new ValidationResult(ErrorMessage);
            return ValidationResult.Success;
        }
    }

类别：

    public class Pharmacy
        {                               
            [MinimumPhoneDigits(10, Area)] 
            public string PhoneNumber
            {
                get
                {
                    return _phoneNumber;
                }
                set
                {
                    _phoneNumber = value;
                }
            }      
            private string _phoneNumber;
            public string Area
            {
                get
                {
                    try
                    {
                        return _phoneNumber.Split(new char[] { '(', ')', '-' }, StringSplitOptions.RemoveEmptyEntries)[0].Trim();
                    }
                    catch
                    {
                        return "";
                    }
                }
            }
}