Update String List Session Variable

Question

I'm trying to make a program in ASP.net where a user selects products from page 1 (default.aspx), clicks a button to put into shopping cart, and it appears in the second page of product list.

List<string> skuList = new List<string>();
if (validation)
{
    foreach (GridViewRow row in GridView1.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            CheckBox chkRow = (row.Cells[0].FindControl("chkRow") as CheckBox);
            if (chkRow.Checked)
            {
                skuList.Add(row.Cells[2].Text);
            }
        }
    }
}
else { Response.Write("<script>alert('At least one product need to be selected!');</script>"); }
Session["sku"] = skuList;

The problem I am having is I can not update Session["sku"].

Goal I want to reach:

on Page 1, user chooses product Number 1,2,3, then the session variable get updated to 1,2,3 on Page 2, user continue to choose product Number 8, then the session variable get updated to 1,2,3,8

I tried to do something like

 Session["sku"] = Session["sku"] + skulistt;

Of course it didn't work.

List<string> skuList = (List<string>)Session["sku"]; Then skuList.Add("New item"); — Abdullah
– Abdullah, Commented May 28, 2014 at 17:53

Erik Philips · Accepted Answer · 2014-05-28 18:07:14Z

It appears you have a misconception about session. The objects stored in session can be strongly-typed, but the typed returned is always object. It would look something like the following (taking session out of the equation):

object myvar = new List<string>();

myvar.Add("mystring"); // will not compile because myvar is defined as object.

To use myvar as a list is needs to be cast to the correct type:

var myvar1 = (List<string>)myvar; 
// or 
var myvar2 = myvar as List<string>; 

myvar1.Add("mystring");
myvar2.Add("mystring");

The difference between myvar and myvar1 is that myvar can hold a reference to any object type, so I could do:

object myvar = new List<string>();
myvar = new WebClient();

but I can't do that with myvar because it's been defined as List<string> which WebClient does not derive from.

So to add a string to the session variable, it needs to be cast as the correct type:

var mylist = (List<string>)Session["sku"];
list.Add("mystring");

However it looks like you just want to replace the value:

session["sku"] = skulistt;

Ehsan Sajjad · Accepted Answer · 2014-05-28 18:37:08Z

1

You have to get List out of Session, add new element in List and then reassign to Session like this:

List<string> list= List<string>();

if(Session["sku"] != null)
     list = (List<string>)Session["sku"];

list.Add("item");

Session["sku"] = list;

UPDATED:

In your case do like this:

Session["sku"] = skulistt;

Change you code like:

List<string> list= List<string>();

if(Session["sku"] != null)
     list = (List<string>)Session["sku"];

if (validation)
{
    foreach (GridViewRow row in GridView1.Rows)
    {
        if (row.RowType == DataControlRowType.DataRow)
        {
            CheckBox chkRow = (row.Cells[0].FindControl("chkRow") as CheckBox);
            if (chkRow.Checked)
            {
                skuList.Add(row.Cells[2].Text);
            }
        }
    }
}
else { Response.Write("<script>alert('At least one product need to be selected!');</script>"); }
Session["sku"] = skuList;

edited May 28, 2014 at 18:37

answered May 28, 2014 at 17:55

Ehsan Sajjad

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10 Comments

CherylG Over a year ago

I got the following error on the line of List.add(skuList)-->Error 1 The best overloaded method match for 'System.Collections.Generic.List<string>.Add(string)' has some invalid arguments

Ehsan Sajjad Over a year ago

so skulisst is itself list then do this: Session["sku"] = skulistt;

Ehsan Sajjad Over a year ago

this is wrong: Session["sku"] =Session["sku"] + skulistt;

Ehsan Sajjad Over a year ago

Session object is different, you cannot concatenate like you do in string case

CherylG Over a year ago

I don't think [code] Session["sku"] = skuList is right; On page 1, skuList is 1,2,3 then on the second page skuList is 8. The session variable would end up with 8, overwritten by skuList.

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