Session state in Asp.Net

• Session state variables are available across all pages, but only for a given single session. Session variables are like single-user global data.
• Session state variables are stored on the web server.
• Session State variables are cleared, when the user session times out. The default is 20 minutes. This is configurable in web.config .

Example:-

session_stste_demo.aspx :-

<div align="center">
        <table>
    <tr>
        <td>
            <b>Name</b>
        </td>
        <td>
            :<asp:TextBox ID="txtName" runat="server">
            </asp:TextBox>
        </td>
    </tr>
    <tr>
        <td>
            <b>Email</b>
        </td>
        <td>
            :<asp:TextBox ID="txtEmail" runat="server">
            </asp:TextBox>
        </td>
    </tr>
    <tr>
        <td colspan="2">
            <asp:Button ID="btnSendData" runat="server"
           Text="Redirect" onclick="btnSendData_Click" />
        </td>
    </tr>
</table>
        </div>

session_stste_demo.aspx.cs :-

protected void btnSendData_Click(object sender, EventArgs e)
    {
        Session["Name"] = txtName.Text;
        Session["Email"] = txtEmail.Text;
        Response.Redirect("~/session_state_2.aspx");
    }

session_stste_webform.aspx.cs :-

<div align="center">
    <table>
    <tr>
        <td>
            <b>Name</b>
        </td>
        <td>
            :<asp:Label ID="lblName" runat="server">
            </asp:Label>
        </td>
    </tr>
    <tr>
        <td>
            <b>Email</b>
        </td>
        <td>
            :<asp:Label ID="lblEmail" runat="server">
            </asp:Label>
        </td>
    </tr>
</table>
    </div>

session_stste_webform.aspx.cs :-

protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["Name"] != null)
        {
            lblName.Text = Session["Name"].ToString();
        }
        if (Session["Email"] != null)
        {
            lblEmail.Text = Session["Email"].ToString();
        }
    }

Points to remember about session state variables:
 
1. Session state variables are stored on the web server by default, and are kept for the life time of a session.
 
2. The default session state mode is InProc.
 
3. The life time of a session is determined by the timeout value in web.config file. The default is 20 minutes. The time-out value can be adjusted according, to your application requirements.
<sessionState mode="InProc" timeout="30"></sessionState>
 
4. Session state variables are available across all pages, but only for a given single session. Session variables are like single-user global data.
 
5. It is always a good practice to check, if a session state variable is null before calling any of its methods, such as ToString(). Otherwise, we may run into runtime NullReferenceExceptions.
 
if (Session["Name"] != null)
{
    lblName.Text = Session["Name"].ToString();    
}
 
6. Application performance can be improved by disabling session state, if it's not required. Session state can be turned off at the page or application level.

To turn of the session state at the page level, set EnableSessionState="False" in the page directive
<%@ Page Language="C#" EnableSessionState="False" AutoEventWireup="true" CodeFile="session_stste_demo.aspx.cs" Inherits="session_stste_demo" %>

To turn of the session state at the application level, set SessionState mode=false in web.config file.
<sessionState mode="Off"></sessionState>