system.nullreferenceException {"Object reference not set to an instance of an object."}

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this is the exception when i try to go to edit form:

system.nullreferenceException {"Object reference not set to an instance of an object."}

my controller:

C#

public ActionResult Edit(int id)
        {
            var ModifierUser = (from u in _db.Utilisateurs
                                where u.IdUser == id
                                select u).First();
            return View(ModifierUser);
        }

        //
        // POST: /Users/Edit/5

        [AcceptVerbs(HttpVerbs.Post)]
        public ActionResult Edit(Utilisateurs ModifierUser)
        {
           
            var OriginalUser = (from u in _db.Utilisateurs
                                where u.IdUser == ModifierUser.IdUser
                                select u).FirstOrDefault();

            if (!ModelState.IsValid)
            {
                return View(OriginalUser);
            }
            _db.ApplyCurrentValues(OriginalUser.EntityKey.EntitySetName,ModifierUser);
            _db.SaveChanges();

            return RedirectToAction("ListUser");

        }

the view:

&

HTML

lt;% foreach (var item in Model) { %>
    <tr>
      
        <td style="width: 78px; height: 32px;">
        
        <% using(Html.BeginForm("Edit","Users",new{id=item.IdUser}))
           { %>
           <input type="image" src="../../Image/edit-validated.png"  alt="Edit" 
                 style="height: 18px" />
                 <%} %></td></tr>

Posted 10-Jan-13 23:25pm

loylmed

Updated 10-Jan-13 23:26pm

AshishChaudha

v2

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Comments

Suvabrata Roy 11-Jan-13 5:28am

First check is your Id is returning anything or not

loylmed 11-Jan-13 5:41am

invalidOperationException was unhandled by user code

1 solution

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Keith Barrow · Answer 1 · 2013-01-11T01:03:00

Hi loymed,

The problem you are having is subtle. The postback Edit overload won't be able to de-serialise the form data back into ModifierUser as binds to items in a list which is a subproperty of Utilisateurs itself. Specifically the new{id=item.IdUser} won't set ModifierUSer.IdUser.
IIRC if you change

XML

using(Html.BeginForm("Edit","Users",new{id=item.IdUser}))

to

XML

using(Html.BeginForm("Edit","Users",new{IdUser=item.IdUser}))

this will populate the value, but I could be mis-remembering what I did (normally I'd check but I'm at work). Additionally, if you are updating this value (and it looks like you are) might be, you are going to have problems distinguishing between the old an new user ids.

There are a few other ways to skin this preserving the old/new id (this same RAZOR as you have currently):

C#

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(int id, /*... other values you need from the form - names must match*/)
{
var OriginalUser = (from u in _db.Utilisateurs
                                where u.IdUser == id
                                select u).FirstOrDefault();
/* Rest of code as before*/
}

or there is also a forms collection you can use which might be neater, depends on what else you are doing.

C#

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(FormsCollection formsCollection)
{
var OriginalUser = (from u in _db.Utilisateurs
                                where u.IdUser == formsCollection["id"]
                                select u).FirstOrDefault();
/* Rest of code as before*/
}