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

I guess there is NO active form while that line is executed. See the documentation [^].

Because one of the parts of frmEmployeeEnroll.ActiveForm is null

It could be either: what you need to do is put a breakpoint on the line, run your application in the debugger, and then look at the two parts when the error occurs to see which it is. Then look back through your other code to find out why.

We can't do that for you: we don't have access to your computer, or know how to get your application to execute that code if we did...

Most likely, frmEmployeeEnroll.ActiveForm is null. This can easily happen because all forms of the application can be inactive at the moment of call. And I cannot guarantee that frmEmployeeEnroll is not null.

You did not find out the exact reason why "Object reference not set to an instance of an object" is thrown, what object was null.

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

Another usefull article: 3 common causes of system.nullreferenceexception[^]

HI follow sergey solution for the theory to understand null reference error.


Try like this,

if (frmEmployeeEnroll != null)
               if (frmEmployeeEnroll.ActiveForm != null)
                   if (frmEmployeeEnroll.ActiveForm.UseWaitCursor)
                       return;

try
{
--------------------
--------------------
}
catch(Exception ex)
{
throw(ex)
}
by using try catch statement you can trace out the error