ValidationAttribute.IsValid Method
Determines whether the specified object is valid.
Namespace: System.ComponentModel.DataAnnotations
Assembly: System.ComponentModel.DataAnnotations (in System.ComponentModel.DataAnnotations.dll)
'Declaration Protected Overridable Function IsValid ( _ value As Object, _ validationContext As ValidationContext _ ) As ValidationResult
Parameters
- value
- Type: System.Object
The object to validate.
- validationContext
- Type: System.ComponentModel.DataAnnotations.ValidationContext
An object that contains information about the validation request.
Return Value
Type: System.ComponentModel.DataAnnotations.ValidationResulttrue if value is valid; otherwise, false.
| Exception | Condition |
|---|---|
| NotImplementedException | The IsValid method is not overridden in the derived class. |
You override the IsValid method to provide the logic for your customized validation check. The GetValidationResult and Validate methods call the IsValid method to determine if the value is valid.
The following example shows a customized validation attribute that derives from ValidationAttribute. The class overrides the IsValid method to test whether the value is valid. By default, the attribute displays an error message that is included as a resource in the application.
Public Class EvenNumberAttribute Inherits ValidationAttribute Public Sub New() MyBase.New(Function() My.Resources.Resource1.EvenNumberError) End Sub Public Sub New(ByVal errorMessage As String) MyBase.New(Function() errorMessage) End Sub Protected Overrides Function IsValid(ByVal value As Object, _ ByVal validationContext As ValidationContext) As ValidationResult If (value = Nothing) Then Return ValidationResult.Success End If Dim convertedValue As Integer Try convertedValue = Convert.ToInt32(value) Catch ex As FormatException Return New ValidationResult(My.Resources.Resource1.ConversionError) End Try If (convertedValue Mod 2 = 0) Then Return ValidationResult.Success Else Return New ValidationResult(FormatErrorMessage(validationContext.DisplayName)) End If End Function End Class
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