ValidationAttribute.IsValid Method (System.ComponentModel.DataAnnotations)

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));
        }
    }
}