Object reference not set to an instance of an object.

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Hi all,
-there is a listview, each row has a check box property,
-on checked check box I want that row to be stored in temp data table,
-But it is generating a error. i.e. Object reference not set to an instance of an object.

DataTable dt = (DataTable)ViewState["CurrentTable"];
DataRow drCurrentRow = null;

C#

cBox = (CheckBox)ListView1.Items[i].FindControl("chckSelect");
if (cBox.Checked)
{
    dt.Rows.Add(ListView1.FindControl("id").ToString());
}

Posted 16-Sep-13 18:37pm

xibit89

Updated 16-Sep-13 18:39pm

v3

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Sergey Alexandrovich Kryukov 17-Sep-13 0:41am

In what line, exactly?
—SA

xibit89 17-Sep-13 0:56am

dt.Rows.Add(ListView1.FindControl("id").ToString());

Mahesh Bailwal 17-Sep-13 0:42am

In which event are you doing this?

xibit89 17-Sep-13 0:56am

Button Click

JoCodes 17-Sep-13 1:06am

Can you quickly check the findcontrol values are null? Try debugging with an immediate window or a watch easily.

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-09-16T18:45:00

I can suggest the most typical reason: FindControl("chckSelect") returns null, and then cBox is assigned to null, and one line below you try to de-reference cBox by getting the value if the property Checked, which throws that exception because you are de-referencing null.

But this is wrong. Most typical scenario is not always what actually happens. You really did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

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