Solved

NUll Reference exception was not handled

Posted on 2006-10-21
4
443 Views
Last Modified: 2010-04-16
Hi there,
I have 2 lists boxes. The 1st one has multiple items. The 2nd listbox is empty. The user selects the items to be transferred to the 2nd listox and hits the ADD button. The process works the other way if the user wants to get rid of the items selected on the 2nd listbox. I just had a chance to check the adding items from listbox1 to listbox2. It works fine, however if the user doesn't choose ant item from the listbox1 and just hits the ADD button I get this following message;

"NUll Reference exception was not handled"
lstChosenSubs.Items.Remove(lstChosenSubs.SelectedItem.ToString());

I guess I need to use the try and catch to handle this exception,right? Any idea how should I use it?
Regards,
0
Comment
Question by:operatortobe
  • 3
4 Comments
 
LVL 48

Accepted Solution

by:
AlexFM earned 250 total points
ID: 17781008
Simple check can solve the problem:

if ( lstChosenSubs.Items.Count > 0 &&  lstChosenSubs.SelectedItem != null )
{
    lstChosenSubs.Items.Remove(lstChosenSubs.SelectedItem.ToString());
}
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 17781021
We need to use exception handling in methods which suppose to throw exceptions - like different I/O methods. Null reference exception is just bug - if you catch it, you can hide your own bugs like using uninitialized references.
0
 

Author Comment

by:operatortobe
ID: 17781221
Hi Alex,
I have tried your code and it works just fine. I have also modified it and applied it to Add button as well. Thanks much. I just wonder what if I wanted to use Try and catch instead... Would it be some thing like this;

try
  {
    if(lstSubjects.Items.Count > 0 && lstSubjects.SelectedItem != null)
            {

                lstChosenSubs.Items.Add(lstSubjects.SelectedItem.ToString());)
       }
   }
catch (System.FormatException caught)
     {
          result.Text = caught.Message;
  }
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 17781310
catch (System.NullReferenceException caught)
0

Featured Post

Free Tool: Postgres Monitoring System

A PHP and Perl based system to collect and display usage statistics from PostgreSQL databases.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction Hi all and welcome to my first article on Experts Exchange. A while ago, someone asked me if i could do some tutorials on object oriented programming. I decided to do them on C#. Now you may ask me, why's that? Well, one of the re…
Exception Handling is in the core of any application that is able to dignify its name. In this article, I'll guide you through the process of writing a DRY (Don't Repeat Yourself) Exception Handling mechanism, using Aspect Oriented Programming.
Email security requires an ever evolving service that stays up to date with counter-evolving threats. The Email Laundry perform Research and Development to ensure their email security service evolves faster than cyber criminals. We apply our Threat…
Are you ready to implement Active Directory best practices without reading 300+ pages? You're in luck. In this webinar hosted by Skyport Systems, you gain insight into Microsoft's latest comprehensive guide, with tips on the best and easiest way…

713 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question