ASP.net RequiredFieldValidator not preventing postback

Question

I have a question about what could stop a RequiredFieldValidator from preventing a postback.

I began working on an older, but simple aspx form and my predecessor use

Answer 1

I had the same problem, but the answer turned out to be quite different. I was also upgrading to .NET validation from server-side hard coded validation.

The issue in my case turned out to be related to the ASP.NET rewriting engine used from the MSDN article URL Rewriting in ASP.NET. Using the default implementation of the "Actionless Form" was the culprit - apparently this one was written based off of an earlier version of .NET and the JavaScript on the form that prevented the postback was not being send to the output because it was missing code.

Anyway, in case anyone else is using this rewriting engine, the solution was to change the default implementation of ActionlessForm to the following:

Public Class Form
    Inherits System.Web.UI.HtmlControls.HtmlForm

    Protected Overrides Sub Render(ByVal writer As System.Web.UI.HtmlTextWriter)
        MyBase.Render(New ActionlessFormHtmlTextWriter(writer))
    End Sub

End Class

Public Class ActionlessFormHtmlTextWriter
    Inherits HtmlTextWriter

    Sub New(ByVal writer As HtmlTextWriter)
        MyBase.New(writer)
        Me.InnerWriter = writer.InnerWriter
    End Sub

    Sub New(ByVal writer As System.IO.TextWriter)
        MyBase.New(writer)
        MyBase.InnerWriter = writer
    End Sub

    Public Overrides Sub WriteAttribute(ByVal name As String, ByVal value As String, ByVal fEncode As Boolean)

        Dim Context As HttpContext = HttpContext.Current

        'Skip the action attribute of the form control.
        If Not (name = "action") OrElse Not Context.Items("ActionAlreadyWritten") Is Nothing Then

            MyBase.WriteAttribute(name, value, fEncode)

        Else
            Context.Items("ActionAlreadyWritten") = True
        End If
    End Sub

End Class

What this does is simply supress the action attribute, but allow any other logic in the framework to run. This should future proof this in case Microsoft decides to change the form again.