Initializing a value through a Session variable

I need to Initialize a value in a Javascript by using a c# literal that makes reference to a Session Variable. I am using the following code

<script type="text/javascript" language="javascript" > 
    var myIndex = <%= !((Session["myIndex"]).Equals(null)||(Session["myIndex"]).Equals("")) ? Session["backgroundIndex"] : "1" %>;

However the code above is giving me a classic Object reference not set to an instance of an object. error. Why? Shouldn't (Session["myIndex"]).Equals(null) capture this particular error?

From stackoverflow

• Are you sure Session["myIndex"] isn't null?

  You should add another short circuit OR check for (Session["myIndex"] == null) and get rid of (Session["myIndex"]).Equals(null).

• object reference error may be because (Session["myIndex"]) is null,

  (Session["myIndex"]).Equals is used to compare value so you can use it you want to compare like (Session["myIndex"]).Equals("yourIndex")

• in the code behind create a protected variable and initialize it there. The main advantage is that you can debug it there. And in plus you can use try catch.

  code-behind

  protected string sessionValue;
  private void Page_Load(...)
  {
  try
  {
  sessionValue = Session["key"].ToString();
  }
  catch
  {
  sessionValue = [defaultValue];
  }
  }
  

  javascript:

  <script>
  var sessionValue = "<%= sessionValue %>";
  </script>
  

  This way you can avoid the crash and do something else if the sessionValue is null or has a defaultValue.

  slugster : -1 I would not be using try/catch as a substitute for a simple *if (Session["key"] == null)* check.... i hope you don't use that method too often?

  GxG : the idea behind try catch is that you can avoid a crash, with if each time the session expires you'll get a crash. Even if i'm not that experienced i believe that this is the safest way to do this. If you could avoid a crash by doing a simple if check then it's okay, but if there is the slightest possibility that the application could crash i suggest the safer try catch version

  slugster : Nope, the page will not crash if the Session expires - you simply get a fresh Session with nothing in it. Stick with the *if null* check, and never make the assumption that your item has been correctly placed into Session.

  GxG : thanks for the advice... If it is not a valuable information that you need to put on the session you can try using request parameters or using a hidden field for storing that string(if it can be converted to a string).

• The problem is that null isn't an object, and the Equals() method can only be used on objects. If you want to check if your Session object is null, you should use (Session["myIndex"] == null). You can also use string.IsNullOrEmpty() for an additional check on empty strings. In that case, your code should be:

  var myIndex = <%= !string.IsNullOrEmpty((string)Session["myIndex"]) ? Session["backgroundIndex"] : "1" %>;
  

  Note: Shouldn't Session["backgroundIndex"] be Session["myIndex"] in this case? Otherwise the null or empty string check is a bit useless in my opinion.

  slugster : -1 for you also... you cannot just do a *string.IsNullOrEmpty(Session["myIndex"])* - it won't even compile as *Session[key]* returns an object, not a string. Your explanation was good though.

  Prutswonder : @slugster: From the context of the sample, it's clear that `Session["myIndex"]` is a string. If it is a different object, then you might as well let the exception be thrown, because you are not expecting it. Besides, the provided sample doesn't check for strings either.

  slugster : I agree the sample doesn't check for (or cast to) strings either. It doesn't matter what is held at that particular index, it is returned as type *object*. At the time i downvoted there were 4 answers, yours was the best but with syntactic errors. If you edit the post i will reverse my downvote.

  Prutswonder : Adding a cast to string is a good idea in this case, so I've updated my sample.

  slugster : Sweet as, downvote reversed :)

• This will work (I have tested it!):

  var myIndex = <%=!string.IsNullOrEmpty( (string)Session["myIndex"] ) ? Session["myIndex"] : "1" %> ;