ASP.Net MVC And Validation Messages

Question

I'm trying to get to grips with the Validation messages in ASP.Net MVC. I have the following view

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master"  Inherits="System.Web.Mvc.ViewPage" %>

<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" runat="server">

    <h2>Create User</h2>

    <%= Html.ValidationSummary("Create was unsuccessful. Please correct the errors and try again.") %>

    <% using (Html.BeginForm()) {%>

        <fieldset>
            <legend>Fields</legend>
            <p>
                Username : <%= Html.TextBox("Username") %>
            </p>
            <p>
                Forename : <%= Html.TextBox("Forename") %>
                <%= Html.ValidationMessage("Forename", "*") %>
            </p>
            <p>
                Surname : <%= Html.TextBox("Surname","") %>
                <%= Html.ValidationMessage("Surname", "*") %>
            </p>
            <p>
                <input type="submit" value="Create" />
            </p>
        </fieldset>

    <% } %>

    <div>
        <%=Html.ActionLink("Back to List", "Index") %>
    </div>

</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="head" runat="server">
    <title><%= ViewData["ProjectTitle"] %> - Create User</title>
</asp:Content>

I then have this post method in my controller that is supposed to display an error message if the surname field is blank, I realise there is no other logic in this function im just trying to get my head round validation.

  [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create(FormCollection formValues)
    {
        if (formValues["Surname"] == string.Empty)
            ViewData.ModelState.AddModelError("Surname", "No way");
        return View("Create");
    }

When I run this and click to save a user the Create method runs fine and adds the error, but then the application falls over, it hightlights the line in the view that creates the surname textbox and says "Not set to an instance of object". It runs fine if I put something in the surname textbox and the error does not get added.

I'm guessing I'm missing something really simple but can work out what.

Any ideas?

Thanks

Gavin

Answer 1

Did you try to remove the second argument on TextBox? It will look for the empty key in ViewData.

the line below

Surname : <%= Html.TextBox("Surname","") %>

needs to be like

Surname : <%= Html.TextBox("Surname") %>

Answer 2

I think I've found a solution adding the setModelValue line below to my method above the line that sets the error makes it work.

            ModelState.SetModelValue("Username", new ValueProviderResult(ValueProvider["Username"].AttemptedValue, formValues["Username"], System.Globalization.CultureInfo.CurrentCulture));
            ModelState.AddModelError("Username", "Invalid Username");

If anyone could explain why this works that would be great, If not I'll accept this answer tommorow. I'd rather not have to do this for ever field I validate unless I really have to.

Answer 3

You should test for Null or empty in your if statement,

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Create(string Username, string Surname,  string Forename)
{
  if (String.IsNullOrEmpty(Surname))
  {
     ModelState.AddModelError("Surname", "No way");
  }

  return View();
}