Exception Title: Check if object is Null

Question

I created table N_Roles_Users in my database, I want to show it's value if username matches with existing login user.

I wrote this code below. But it is generating exception that check if object is Null.

// currentUser="UserA";
public List<string> GetUserRoles( string currentUser)
{
        N_Roles_Users allroles = new N_Roles_Users(); //N_Roles_Users is database table name. 
        List<string> roleslist = new List<string>();
        List<char> temp = new List<char>();
        temp = allroles.user_name.ToList();
        List<char> tempa = new List<char>();
        tempa = allroles.role_name.ToList();

        for (int i = 0; i < temp.Count; i++) // Loop through List with for
        {
            if (currentUser == temp[i].ToString())
            {
                roleslist.Add(tempa[i].ToString());
                MessageBox.Show(tempa[i].ToString());
            }
        }

        return roleslist;
}

Can anyone guide me how to resolve this problem?

On which line is the exception generated? Please provide us with the stacktrace and exact exception type `System.InvalidOperationException` or maybe a `System.NullReferenceException` or what kind of exception? — SynerCoder, Aug 21 '13 at 09:36
on all lists. i removed list one by one to check that which list is creating this issue, but on each list this Exception generates. I executed queries to check it out that are values present in table or not. Values were present. I don't know what's wrong with it. — Zoya Sheikh, Aug 21 '13 at 09:38
You make a new instance of `N_Roles_Users`, what is in the constructor? do you initialize everything? — Sayse, Aug 21 '13 at 09:39
@ZoyaSheikh . I think that column name return null (empty) values , so you get this error. please look my answer , check that condition or check that column has any values there ? .. — Ramesh Rajendran, Aug 21 '13 at 09:42
possible duplicate of [What is a NullReferenceException in .NET and how do I fix it?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net-and-how-do-i-fix-it) — CodeCaster, Aug 21 '13 at 09:42
See my answer . Check that condition : http://stackoverflow.com/a/18353979/2218635 — Ramesh Rajendran, Aug 21 '13 at 10:12

score 0 · Answer 1 · answered Aug 21 '13 at 09:39

0

temp = allroles.user_name.ToList(); is the line of exception i guess.

set allroles.user_name = "some value" before

this line

temp = allroles.user_name.ToList();

Happy Coding :)

answered Aug 21 '13 at 09:39

Abhishek Singh

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Hello Zoya. What do you mean by shows nothing. Nothing is printed on console or what ? – Abhishek Singh Aug 21 '13 at 09:57
yes, i wrote textbox1.Text=temp[1].ToString(); ... But nothing printed – Zoya Sheikh Aug 21 '13 at 10:01

score 0 · Answer 2 · answered Aug 21 '13 at 09:40

Check this condition

// currentUser="UserA";

public List<string> GetUserRoles( string currentUser)
        {
        N_Roles_Users allroles = new N_Roles_Users();
        List<string> roleslist = new List<string>();
        List<char> temp = new List<char>();
         **if(allroles.user_name.ToList()!=null &&  allroles.user_name.ToList().Count!=0)
          {
         temp = allroles.user_name.ToList();
         }**
        List<char> tempa = new List<char>();
        tempa = allroles.role_name.ToList();

        for (int i = 0; i < temp.Count; i++) // Loop through List with for
            {
            if (currentUser == temp[i].ToString())
                {
                roleslist.Add(tempa[i].ToString());
                MessageBox.Show(tempa[i].ToString());
                }
            }
        return roleslist;
        }

if `user_name` is null you will still get an NRE here – Sayse Aug 21 '13 at 09:42 — Sayse, Aug 21 '13 at 09:42

Exception Title: Check if object is Null

2 Answers2