example16.cs

public sealed class ValidatePasswordLengthAttribute : ValidationAttribute
    {
        private const string _defaultErrorMessage = "'{0}' must be at least {1} characters long.";
        private readonly int _minCharacters = Membership.Provider.MinRequiredPasswordLength;
 
        public ValidatePasswordLengthAttribute()
            : base(_defaultErrorMessage)
        {
        }
 
        public override string FormatErrorMessage(string name)
        {
            return String.Format(CultureInfo.CurrentUICulture, ErrorMessageString,
                name, _minCharacters);
        }
 
        public override bool IsValid(object value)
        {
            string valueAsString = value as string;
            return (valueAsString != null && valueAsString.Length >= _minCharacters);
        }
    }