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ValidationAttribute.IsValid Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Determines whether the specified object is valid.

Namespace:  System.ComponentModel.DataAnnotations
Assembly:  System.ComponentModel.DataAnnotations (in System.ComponentModel.DataAnnotations.dll)

Syntax

'Declaration
Protected Overridable Function IsValid ( _
    value As Object, _
    validationContext As ValidationContext _
) As ValidationResult

protected virtual ValidationResult IsValid(
    Object value,
    ValidationContext validationContext
)

Parameters

Return Value

Type: System.ComponentModel.DataAnnotations.ValidationResult
true if value is valid; otherwise, false.

Exceptions

Exception Condition
NotImplementedException

The IsValid method is not overridden in the derived class.

Remarks

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.

Examples

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

public class EvenNumberAttribute : ValidationAttribute
{
    public EvenNumberAttribute() : base(() => Resource1.EvenNumberError) { }
    public EvenNumberAttribute(string errorMessage) : base(() => errorMessage) { }

    protected override ValidationResult IsValid(object value, 
        ValidationContext validationContext)
    {
        if (value == null)
        {
            return ValidationResult.Success;
        }

        int convertedValue;
        try
        {
            convertedValue = Convert.ToInt32(value);
        }
        catch (FormatException)
        {
            return new ValidationResult(Resource1.ConversionError);
        }

        if (convertedValue % 2 == 0)
        {
            return ValidationResult.Success;
        }
        else
        {
            return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
        }
    }
}

Version Information

Silverlight

Supported in: 5, 4, 3

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.