Usage of Session object in ASP.NET

Question

I've just been given a new task to bootstrap a website created by someone else. But I'm absolutely new to Web. The website is in ASP.NET,C#. The code itself is not hard to understand except for the Session object. I don't understand where, how and why it's used.Could please someone explain the usage of Session object with a possible example?

P.S. What would these two lines mean?

    lblPensValue.Text = sh.pensDec((string)Session["connSTR"], 113, 23);
and
    if ((string)Session["connSTR"] == null)

Answer 1

Session is used to store data for the user's session on the web site. (this data store is per-user-browser session, and is subject to being wiped at any time by various application events)

It is generally used to store information across multiple page views in a user's session (ie. visit) to your website.

It can be used anywhere in code that runs in the context of the user's session; meaning inside a page, or in the appropriate application lifecycle events which run in the context of a session (such as Session Start)

As for your samples;

The first one, I can't fully explain, as I do not know what the function sh.pensDec() is supposed to do.

The second one is checking to make sure there is a value stored in that session variable, before running the code that follows.

Answer 2

HTTP by nature is stateless. The WebServer doesn't know any details after it processes the request and sends back to the client. Thus, any subsequent requests are like fresh requests to the server.

To Enable the Server to remember & subsequently recognize what it served to the client, ASP.NET uses various mechanisms of which Session is one of them.

Session is created per user. So, in your Page, you are fetching the "connSTR" are storing it. Whenever a subsequent request comes from the same user, by querying Session with the key

Session["connSTR"]

you get back its value. Since Session is an Object, its casted as a string in your code.