c# Object reference not set to an instance of an object.

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Hi,

I'm running this code in the Edit View and it works fine however in the Create View it generate Object reference not set to an instance of an object error for this specific line

C#

foreach(var evnt in s)

I can't seen to grasp the issue.

C#

<div class="form-group">
           <div class="col-md-offset-2 col-md-10">
               <table>
                   <tr>
                       @{
                                    int cnt = 0;
                       List<GestionSinistresA.ViewModels.StatutFSEvenement>
                           evnts = ViewBag.Evenements;
                           foreach(var evnt in evnts)
                           {
                               if(cnt++ %3 == 0)
                               {
                                   @:</tr><tr>

                               }

                               @:<td>
                                   <input type="checkbox"
                                          name="sinistreEvents"
                                          value="@evnt.EvenementID"
                                          @(Html.Raw(evnt.designee ? "checked=\"checked\"" : "")) />
                                   @evnt.CodeEvenement
                               @:</td>
                               }

                           @:</tr>
                   }
               </table>
           </div>

       </div>

Thanks

Posted 15-Jul-15 13:38pm

Sabi1610

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Comments

[no name] 15-Jul-15 19:59pm

"I can't seen to grasp the issue", it means exactly what it says. You have an object that is null.

Paulo Zemek 15-Jul-15 20:29pm

I don't see you checking for null anywhere.
If ViewBag is null, you will have that exception.
If evnts is null, you will have that exception.
I don't know your actual collection, so if an evnt inside a valid evnts is null, then you will have that exception.
If none of those was supposed to be null, it doesn't mean they will never be null. It can mean that somewhere else has a bug and a null is arriving to this piece of code.

Sergey Alexandrovich Kryukov 15-Jul-15 21:09pm

If the inquirer correctly pointed out the line where the exception is thrown, it's "s". Please see my answer.
—SA

Paulo Zemek 15-Jul-15 21:35pm

He shows a foreach over s... and then it seems the foreach is over evnts... so I got confused. Anyways, I am looking at your solution now.

Sergey Alexandrovich Kryukov 16-Jul-15 0:59am

This is because the inquirer's observation could be not accurate, which happens way too often. I have nothing to do but rely on the claim of our inquirer, ignoring further detail. That's why I prefer to suggest the methodical directions for debugging, to complement those not very valuable suggestions on what happened, which are quite trivial. That's why I add "If you correctly pointed out..."
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-07-15T15:09:00

If your correctly pointed out the line where the exception is thrown, s is null. You could see what's wrong in not time if you used the debugger. Really, you cannot ask such questions each time it happens; you really need to learn to cope with such situations on your own.

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object".

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx,
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx.

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx.

Good luck,

—SA