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

它认为实际物体本身无效。您有一分不变的物体,你又试图获取该物上的财产,因此,操作时间将推出。如果物体在试图与成员接触之前先无效,你最好不要检查:

友情链接