question about Session

Question

Hi,

this code works perfect (without the last line!). The elements of list<T> are retained by the Session variable after each postback. But i'm wondering how it can work without the last line: Session["time"] = time; . When a new element is added to the list, if Session["time"] is not present, then it's not updated and doesn't contain the new element. According to me, the line time = (List<int>)Session["time"]; can't contain anyyhing.

Any explanation for this: why is that line Session["time"] = time; not necessary?

Thanks

V

using System;
using System.Collections.Generic;

public partial class WebForm : System.Web.UI.Page
{
List<int> time = new List<int>();

protected void Page_Load(object sender, EventArgs e)
{
TextBox1.Focus();
if (!Page.IsPostBack)
{
Session["time"] = time; // empty
}
}
protected void TextBox1_TextChanged(object sender, EventArgs e)
{
Label1.Text = "";
time = (List<int>)Session["time"];
time.Add(Convert.ToInt32(TextBox1.Text));
time.Sort();
for (int i=0;i< time.Count;i++)
Label1.Text += time[i].ToString() + " ";
TextBox1.Text = "";
//Session["time"] = time; // works without this line
}
}

Valerie Meunier · Answer

May I suggest that you copy/paste this code and try yourself in VS. In aspx-file, you only need a label and a textbox. This is the first line: Thanks

Valerie Meunier · Answer

I tested it with a label inside the IF(): the first time, the label got a value, after that no. I'm sure it(s running properly: if (!Page.IsPostBack) { Session["time"] = time; // empty } How can i test it with the debugger?

Sachin Singh · Answer

if if (!Page.IsPostBack) { Session["time"] = time; // empty } if the above line is not executing then there is no way session could be set. Have you tested it with debugger?

Valerie Meunier · Answer

if i do that, i see only the last added value.

Sachin Singh · Answer

Are you sure if you remove time = (List )Session["time"]; then it stops working?

Valerie Meunier · Answer

Thanks for replying, but there must be a reason for that. No idea?

Sachin Singh · Answer

put a debugger at below line if (!Page.IsPostBack) { Session["time"] = time; // empty } if with each text change the flow is not entering inside the above curley braces (and setting session) (obviously it shouldn't enter for postbacks) then yes, it is strange . Your session should be empty.

Valerie Meunier · Answer

I wonder why nobody has tried. I did this as test: if (!Page.IsPostBack) { Label2.Text += "not postback"; Session["time"] = time; // empty } else { Label2.Text += "postback"; } And this gives not postback postback postback postback ... This proves that it's executed only one time. Try yourself.

Munib Butt · Answer

Somehow, the below is executed each time. if (!Page.IsPostBack) { Session["time"] = time; // empty } Otherwise, the session cannot be set.