c# - RequiredIf item exists in an array

Question

I am trying to create a custom RequiredIf attribute which requires fields based on their existence in an array. The array is part of the model as illustrated in the example model below, the FamilyHistoryCustomerItem has one field of type string.

public class FamilyHistory {

    [CanBeNull] public List<FamilyHistoryCustomerItem> FamilyHistoryCustomerItems { get; set; }

    [RequiredIfItemInCollection(FamilyHistoryCustomerItems, MedicalConditions.ColonOrBowelCancer)]
    public bool ColonOrBowelImmediateFamilyHadColonCancerHnpccOrLynchSyndrome { get; set; }
}

This is a simple custom attribute I have created, the attribute throws an error when I try and pass the array because the array is not initialised. Is this even possible, this is my first time working with these so please be easy on me :)

public class RequiredIfItemInCollection : ValidationAttribute
    {
        private readonly string[] collection;
        private readonly string item;

        public RequiredIfItemInCollection(string[] items, string item)
        {
            if (items.IsNullOrEmpty() || item.IsNullOrEmpty())
                throw new ArgumentOutOfRangeException(nameof(items), "Nothing was provided");

            collection = items;
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            return collection.Contains(item)
                    ? ValidationResult.Success
                    : new ValidationResult(this.ErrorMessage);
        }
    }

Answer 1

等待大神答复