NullReferenceException was unhandled

Question

I'm just getting the hang of Lightswitch, but I keep getting the null reference exception error when I'm trying to find out if a selected item in a datagrid contains the letters "CMP". I look all over the place but I think I'm doing something wrong. Here is my code for reference:

if(string.IsNullOrWhiteSpace(this.location.SelectedItem.locationID))
        {
            this.ShowMessageBox("test"); //not sure what to put there so I just made something up
        }
        else if (this.location.SelectedItem.locationID.Contains("CMP"))
        {
            this.FindControl("datePurchased").IsVisible = true;
            this.FindControl("age").IsVisible = true;
            this.FindControl("userList").IsVisible = true;
        }
        else
        {
                this.FindControl("datePurchased").IsVisible = false;
                this.FindControl("age").IsVisible = false;
                this.FindControl("userList").IsVisible = false;
        }

I also tried

if(this.location.selecteditem.locationID != null)

if(string.IsNullOrEmpty)

but it always throws me the same error. Any help would be much appreciated!

probably your this.location.selecteditem variable or this.location is null — Sercan Ozdemir, Apr 28 '14 at 05:43
its a cell in a datagrid though, and there are some values there already. When I debugged it, it shows that there is a value, then all of a sudden it said its null. — jester113, Apr 28 '14 at 05:44
i dont know how lightswitch works, but in asp.net if you select an item and dont keep it on postbacks, you cant reach them back, i think theres something like that in here. — Sercan Ozdemir, Apr 28 '14 at 05:46
sorry I'm still learning the ropes of programming...what do you mean by that? can you give me an example? — jester113, Apr 28 '14 at 05:49
as i said i dont know lightswitch but, please read [here](http://stackoverflow.com/questions/18406795/dropdownlist-not-keeping-the-selected-item-after-postback) — Sercan Ozdemir, Apr 28 '14 at 05:52
What do you mean by "it said its null"? What said that *what* is null? What do you mean by "there is a value" - there is a value for *what*, exactly? What do you expect to happen if nothing is selected? — Jon Skeet, Apr 28 '14 at 05:53
possible duplicate of [What is a NullReferenceException and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — nvoigt, Apr 28 '14 at 05:56
when i hover over the selecteditem part when i set a breakpoint, i get the popup saying "this.location.selecteditem | null" — jester113, Apr 28 '14 at 05:58
hi nvoigt, yup i tried those. I tried != null = null == null and other checks stated on that post. Still throws me that exception. — jester113, Apr 28 '14 at 05:59

score 2 · Accepted Answer · answered Apr 28 '14 at 06:02

I guss this.location or this.location.selecteditem may be null, So you got that error. So please try this if condition instead of your if condition way

if(this.location != null && this.location.selecteditem !=null && this.location.selecteditem.locationID != null)
{
       //Write your code here 
}

So your final code look like

        if(this.location == null && this.location.selecteditem ==null && this.location.selecteditem.locationID == null)
        {
          this.ShowMessageBox("test"); //not sure what to put there so I just made something up
        }    

        else if (this.location.SelectedItem.locationID.Contains("CMP"))
        {
            this.FindControl("datePurchased").IsVisible = true;
            this.FindControl("age").IsVisible = true;
            this.FindControl("userList").IsVisible = true;
        }
        else
        {
                this.FindControl("datePurchased").IsVisible = false;
                this.FindControl("age").IsVisible = false;
                this.FindControl("userList").IsVisible = false;
        }

awesome! it stopped throwing the exception...but now the code inside doesnt fire >.> but at least the exception is gone ^o^ — jester113, Apr 28 '14 at 06:06
Cool! I have updated my answer. Please take a look that, and please use break point for which values are threw null. — , Apr 28 '14 at 06:09
Thios is perfect its working now! thanks so much! I put the code in its own method and called it everytime the selection was changed and its works now! thanks so much! — jester113, Apr 28 '14 at 06:12

NullReferenceException was unhandled

1 Answers1