Question

I have some problem in understanding how does the asp.net mvc deal with Null values .
In the first scenario i have the following action method:-

[HttpPost]
        public ActionResult Delete(int labtestid, int visitid)
        {
try
            {
                var vlr = repository.GetVisitLabResult(labtestid,visitid);
                string desc = vlr.LabTest.Description; 
                repository.DeleteVisitLabResult(vlr);
                repository.Save();
                return Json(new { IsSuccess = "True", id = labtestid, description =    desc }, JsonRequestBehavior.AllowGet);
            }

Incase the repository method var vlr = repository.GetVisitLabResult(labtestid,visitid); does not return any result (var vlr is null) then the following exception will be raised on the string desc = vlr.LabTest.Description; NullReferenceException was unhandled by user code. So why did the framework raise an exception instead of just assigning a null value to the string desc !!!
BR

Answer 1

It looks like the actual object itself is null. You have a null object and you’re trying to access properties on it, hence the runtime will throw a NullReferenceException. You’re best off checking if the object is null first before trying to access it’s members 🙂