C# 自定义Attribute

 1 // 根据不同的region 设定name不同的最大长度和提示信息Region=APAC时，Name最长可以255，其他的Region最长时30
 2 
 3  public class QueryAddModels
 4     {
 5         [Required(ErrorMessage = "Please input Name")]        
 6         [RegularExpression(@"^([A-Za-z0-9_-]){1,300}$", ErrorMessage = "Only accept A-Z a-z 0-9 _ and -")]
 7         //[MaxLength(255, ErrorMessage = "The maximum allowable length is 255")]   
 8         [NameMaxLength] // 自定义
 9         public string Name
10         {
11             get; set;
12         }
13 
14         [Required(ErrorMessage = "Please select Region")]
15         public string Region
16         {
17             get; set;
18         }
19     
20         [UserIDValidation] //自定义
21         public string UserID { get; set; }
22 
23 }
24 
25 // NameMaxLength， Attribute 
26 
27  public class NameMaxLength : MaxLengthAttribute
28     { 
29         protected override ValidationResult IsValid(object value, ValidationContext validationContext)
30         {
31             var region = validationContext.ObjectType.GetProperty("Region")
32                 .GetValue(validationContext.ObjectInstance, null);
33 
34             var name = validationContext.ObjectType.GetProperty("Name")
35                 .GetValue(validationContext.ObjectInstance, null);
36 
37             if (region != null)
38             {
39                 if (String.Equals(region.ToString(), "APAC") && name != null && name.ToString().Length>255)
40                 {
41                     return new ValidationResult("The maximum allowable length is 255.");
42                 }
43                 else if (!String.Equals(region.ToString(), "APAC") && name != null && name.ToString().Length > 30)
44                 {
45                     return new ValidationResult("The maximum allowable length is 30.");
46                 }
47             }
48             return ValidationResult.Success;
49         }
50     }
51 
52  public class UserIDValidation : ValidationAttribute
53     {
54         protected override ValidationResult IsValid(object value, ValidationContext validationContext)
55         {
56             var newUserID = validationContext.ObjectType.GetProperty("UserID")
57                 .GetValue(validationContext.ObjectInstance, null);
58 
59             if (newUserID !=null && !string.IsNullOrEmpty(newUserID .ToString()))
60             {
61                 if (newUserID .ToString().ToUpper() != HttpContext.Current.Session["UserID "].ToString().ToUpper())
62                     return new ValidationResult("UserID can‘be changed");
63                 else
64                     return ValidationResult.Success;
65             }
66             return new ValidationResult("UserID can‘t be empty");
67         }
68 
69     }