MVC 4 custom validation attribute firing twice on server side - asp.net-mvc

Question

I'm using custom validation requiredconditional that inherits from RequiredAttribute to conditionally require certain fields. This works beautifully everywhere except in once case and I cannot figure out what is happening. It is calling the IsValid method twice for one property in the model (the client side validation works perfectly) The model has 2 properties using this attribute but only one has the issue. At first I thought it was because one of my conditions was a checkbox and it was posting back both the checked value and the hidden value but I tried using radio buttons instead and even a hidden value but had the same results in all cases. Here is my view (simplified for testing):
#ModelType List(Of eLADNETBusiness.AdditionalInterest)
#Code
ViewData("Title") = "Bind Coverage Entry"
End Code
<h2>Bind Coverage Entry</h2>
#Using Html.BeginForm()
#Html.AntiForgeryToken()
#Html.Hidden("hullValue", ViewBag.HullValue)
Dim currentCount As Integer = 0
#For count As Integer = 0 To Model.Count - 1
currentCount = count
#<div class="editor-label">
#Html.LabelFor(Function(model) model(currentCount).LienholderAmount)
</div>
#<div class="editor-field">
#Html.EditorFor(Function(model) model(currentCount).LienholderAmount)
#Html.ValidationMessageFor(Function(model) model(currentCount).LienholderAmount)
</div>
#<div>
#Html.EditorFor(Function(model) model(currentCount).Lienholder90Percent)
</div>
Next
#<p>
<input type="submit" value="Continue" />
</p>
End Using
And here is my model (simplified for testing):
<DataContract()> _
Public Class AdditionalInterest
<DataMember()> _
Public Property ID As Integer = 0
<RequiredConditional("Lienholder90Percent", False, ErrorMessage:="Enter Breach of Warranty lienamount or select 90 percent of insured value")> _
<Display(Name:="Lienholder Amount")> _
<DataMember()> _
Public Property LienholderAmount As Nullable(Of Integer)
<DataMember()> _
Public Property Lienholder90Percent As Boolean
End Class
And my requiredconditional attribute:
Imports System.Collections.Generic
Imports System.Linq
Imports System.ComponentModel.DataAnnotations
Imports System.Web.Mvc
Imports System.Collections
Imports System.Text
Public Class RequiredConditional
Inherits RequiredAttribute
Implements IClientValidatable
Private Property PropertyNames() As String()
Private Property DesiredValues() As Object()
Public Sub New(comparePropertyNames As String(), comparePropertyDesiredValues As Object())
PropertyNames = comparePropertyNames
DesiredValues = comparePropertyDesiredValues
End Sub
Public Sub New(comparePropertyNames As String, comparePropertyDesiredValues As Object)
PropertyNames = New String() {comparePropertyNames}
DesiredValues = New String() {comparePropertyDesiredValues}
End Sub
Protected Overrides Function IsValid(value As Object, context As ValidationContext) As ValidationResult
Dim instance As Object = context.ObjectInstance
Dim type As Type = instance.GetType()
Dim propertyvalue As Object
Dim trueConditions As Integer = 0
For count As Integer = 0 To PropertyNames.Count - 1
propertyvalue = type.GetProperty(PropertyNames(count)).GetValue(instance, Nothing)
If Not propertyvalue Is Nothing Then
If DesiredValues.Count >= count + 1 Then
If propertyvalue.ToString() = DesiredValues(count).ToString() Then
trueConditions += 1
End If
End If
End If
Next
'if all conditions are met, validate value
If trueConditions = PropertyNames.Count And trueConditions = DesiredValues.Count Then
Dim result As ValidationResult = MyBase.IsValid(value, context)
Return result
End If
Return ValidationResult.Success
End Function
Public Function GetClientValidationRules(metadata As System.Web.Mvc.ModelMetadata, context As System.Web.Mvc.ControllerContext) As System.Collections.Generic.IEnumerable(Of System.Web.Mvc.ModelClientValidationRule) _
Implements System.Web.Mvc.IClientValidatable.GetClientValidationRules
Dim results As New List(Of ModelClientValidationRule)
Dim rule = New ModelClientValidationRule With {.ErrorMessage = FormatErrorMessage(metadata.GetDisplayName()), .ValidationType = "requiredif"}
Dim depProp As String = String.Empty
Dim sbProp As New StringBuilder()
Dim sbTarget As New StringBuilder()
Dim helper As New ValidationHelper
For count As Integer = 0 To PropertyNames.Count - 1
Dim prop As String = PropertyNames(count)
depProp = helper.BuildDependentPropertyName(metadata, TryCast(context, ViewContext), prop)
sbProp.AppendFormat("|{0}", depProp)
Dim targetValue As String = String.Empty
If DesiredValues.Count >= count + 1 Then
targetValue = (If(DesiredValues(count), "")).ToString()
End If
If DesiredValues(count).GetType() = GetType(Boolean) Then
targetValue = DesiredValues(count).ToString.ToLower
End If
sbTarget.AppendFormat("|{0}", targetValue)
Next
rule.ValidationParameters.Add("dependentproperty", sbProp.ToString().TrimStart("|"))
rule.ValidationParameters.Add("targetvalue", sbTarget.ToString().TrimStart("|"))
results.Add(rule)
Return results
End Function
End Class
So when I click submit and debug into the requiredconditional attribute, the lienholderamount property hits IsValid twice. The first time it hits, the value of Lienholder90Percent is False even though in the model it is true and was true on the form (and passed client side validation) so fails validation at that point. Then hits again and Lienholder90Percent is True (which is correct) and passes validation. But since it failed on the first one, it still fails and show the error message. You'll notice that the model is a list but for testing purposes, I'm only sending one and still getting the same results. Can't figure out why it is only happening with this one property. Hope it is something easy I just can't see. I've spent all day trying to figure this out. Like I said, I use this attribute quite a bit and works great. Can't find a difference for this case.

Answer 1

Inherit from ValidationAttribute instead of RequiredAttribute.
RequiredAttribute's IsValid is called right after the property is filled, whereas the ValidationAttribute's IsValid is called after the whole model is filled (which would make sense for more complex validation).