用户输入验证——自定义数据注解

 [Required]
        [Display(Name = "User name")]
        public string UserName { get; set; }

    public class MaxWordsAttribute : ValidationAttribute
    {
        private readonly int _maxWords;
        public MaxWordsAttribute(int maxWords):base("{0} too many words.")
        {
            _maxWords = maxWords;
        }
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if(value!=null)
            {
                var valueAsString = value.ToString();
                if (valueAsString.Split(‘ ‘).Length > _maxWords)
                {
                    var errorMessage=FormatErrorMessage(validationContext.DisplayName);
                    return new ValidationResult(errorMessage);
                }
            }
            return ValidationResult.Success;
        }

    }

 [Required]
        [Display(Name = "User name")]
        [MaxWords(2,ErrorMessage="{0} 太多单词了")]
        public string UserName { get; set; }