当其他属性应用于类时，CustomValidationAttribute 不起作用
重现：
Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations
Module Module1
Sub Main()
Dim type = GetType(Contact)
TypeDescriptor.AddProviderTransparent(
New AssociatedMetadataTypeTypeDescriptionProvider(type), type)
Dim contact As New Contact
Dim context As New ValidationContext(contact, Nothing, Nothing)
Dim errors As New List(Of ValidationResult)
Dim result = Validator.TryValidateObject(contact, context, errors, True)
End Sub
End Module
<CustomValidation(GetType(Contact.ContactMd), "*********************")>
<MetadataType(GetType(Contact.ContactMd))>
Public Class Contact
Public Property Email As String
Public Property EmailRepeat As String
Public Class ContactMd
'<Required()>
Public Property Email
'<Required()>
Public Property EmailRepeat
Public Shared Function ValidateEmails(ByVal contact As Contact) _
As ValidationResult
Return If(contact.Email = contact.EmailRepeat,
ValidationResult.Success,
New ValidationResult("Fail!"))
End Function
End Class
End Class
上面的代码会抛出异常：CustomValidationAttribute 方法“************************”在“ContactMd”类型中不存在，或者不是公共和静态的。
此异常是合理的，这是事情正在发挥作用的标志。 一旦我取消注释 Md 类中属性的 Required 属性，就不会抛出异常，这意味着验证系统不会同时验证属性类型属性和类级属性。
有什么解决办法吗？
Reproduction:
Imports System.ComponentModel
Imports System.ComponentModel.DataAnnotations
Module Module1
Sub Main()
Dim type = GetType(Contact)
TypeDescriptor.AddProviderTransparent(
New AssociatedMetadataTypeTypeDescriptionProvider(type), type)
Dim contact As New Contact
Dim context As New ValidationContext(contact, Nothing, Nothing)
Dim errors As New List(Of ValidationResult)
Dim result = Validator.TryValidateObject(contact, context, errors, True)
End Sub
End Module
<CustomValidation(GetType(Contact.ContactMd), "*********************")>
<MetadataType(GetType(Contact.ContactMd))>
Public Class Contact
Public Property Email As String
Public Property EmailRepeat As String
Public Class ContactMd
'<Required()>
Public Property Email
'<Required()>
Public Property EmailRepeat
Public Shared Function ValidateEmails(ByVal contact As Contact) _
As ValidationResult
Return If(contact.Email = contact.EmailRepeat,
ValidationResult.Success,
New ValidationResult("Fail!"))
End Function
End Class
End Class
The above code will throw an exception:The CustomValidationAttribute method '*********************' does not exist in type 'ContactMd' or is not public and static.
This exception is justified and it's a sign that things are working.
Once I uncomment the Required attributes on the properties in the Md class, the exception will not be throw, which means, the validation system doesn't validate for both property-typed attributes and class-level attributes.
Any workaround?
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答案是，验证系统首先验证属性验证属性（在本例中为
Required属性），并且只有在对象传递了该属性时才会继续执行CustomValidationAttribute属性。因此，根据上面的再现，将该行更改
为类似的内容（允许实体通过属性验证）：
将抛出预期的异常。
The answer is, that the validation system validates the property validation attributes first (the
Requiredattributes in this case), and will only proceed to theCustomValidationAttributeif the object passed the property attributes.So per the reproduction above, changing the line
to something like (allowing the enitity to pass the property validation):
Will throw the expected exception.
CustomValidationAttribute 指定的方法的签名必须是：
VB：
C#：
如果验证正常，则应返回 ValidationResult.Success。
The signature for the method specified by the CustomValidationAttribute must be:
VB:
C#:
If the validation is OK, it should return ValidationResult.Success.