Question

Probably a C# noob question, so don’t flame me. I was trying to do this:

if (ConfigurationManager.ConnectionStrings["PrimaryConnectionString"].ConnectionString != null)
{
    // ...
}

But I kept getting a System.NullReferenceException. I thought since it returns a string that I could just check for null and move on. It took me a while to find the right way to do it:

ConnectionStringSettings cs = ConfigurationManager.ConnectionStrings["PrimaryConnectionString"];
if (cs != null)
{
    this.Connection.ConnectionString = cs.ConnectionString;
}

So in other instances, like checking a Session object for some value I would do a check for null like this:

if (Session["EmployeeID"] != null)
{
    _EmployeeID = System.Convert.ToInt32(Session["EmployeeID"]);
}

So I just wanted to know how do you know when you can or can’t do a check for null?

Answer 1

Your null reference exception happened in parent object (ConfigurationManager.ConnectionStrings[“PrimaryConnectionString”]). Once you check it also, you are fine.

try this:

if ((ConfigurationManager.ConnectionStrings["PrimaryConnectionString"] != null)
&& (ConfigurationManager.ConnectionStrings["PrimaryConnectionString"].ConnectionString != null))
  { etc etc }

Notice that if you use more methods from it, it would be useful to separate these checks.