How to solve this kind of error? Please help!

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VB

System.Web.HttpUnhandledException: Exception of type 'System.Web.HttpUnhandledException' was thrown. ---> System.NullReferenceException: Object reference not set to an instance of an object.

Posted 20-Jan-14 1:55am

Richard4

Updated 20-Jan-14 1:59am

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Karthik_Mahalingam 20-Jan-14 7:59am

post your code..

Kornfeld Eliyahu Peter 20-Jan-14 7:59am

NullReferenceException means that you try to use and object was not initialized prior to it...
BUT! It's impossible to tell more without your code - please post it with the question...

sp_suresh 20-Jan-14 7:59am

this means the you are passing null to object

Richard4 20-Jan-14 8:06am

I used Me.Session.Add("con", con)
sometimes it works but sometimes doesn't work.

Is it possible that the session will expire automatically?

<sessionstate mode="InProc" timeout="20">
<customerrors defaultredirect="Login.aspx">

Richard4 20-Jan-14 8:12am

I decide to replace new session data of users every page load. but still i got same error.
I don't understand, i can't control the error.

sp_suresh 20-Jan-14 9:32am

no session will not expire automatically but may expire after session timeout.Your session value is somewhere reset try to find out where this value reset bec'se this is only reason.Try to find scenarao where value reset

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phil.o · Accepted Answer · 2014-01-20T01:59:00

Solution 1

You can prevent this kind of error to happen by never assuming that an object has been correctly initialized before using it (i.e., always check for a null value before using any class).

In code, here's a small example describing the general idea:

C#

// Here myObject can be any reference-type variable
if (myobject != null) {
   // Do something with myObject
}
else {
   // Obviously there is a problem, myObject should not be null, but it is.
   // You have to decide here what to do in this case.
}

Posted 20-Jan-14 1:59am

phil.o

Comments

Rahul VB 20-Jan-14 12:31pm

hello sir,
thats correct, very nice. What i used to do was to add a break point on that line and hover the mouse just above that line to see which object is null. Obviously the object is not initialized. Am i correct Sir?
Thanks,
-Rahul

Richard4 20-Jan-14 23:45pm

In my Class I declare Dim xx As String = Nothing

I used Global.asax to display the error Response.Write("<pre>"& err.InnerException.Message &"</pre>")

I try to put a break point on my code, but i didn't seen Null after executing my code and still Global.asax response "Object reference not set to an instance of an object."

phil.o 21-Jan-14 7:09am

We would need the complete exception message (along with stack trace) to determine which line of code exactly is throwing the NullReferenceException.

Could you declare:
Dim xx as String = String.Empty
instead?
This way your xx variable would not be null (Nothing in VB).

Richard4 22-Jan-14 11:39am

Thank you for your comments and suggestions.

What i have to do right now is just to put my web app to production, so that i can really know what is the problem.

richard