How should session variables be properly used for paging and sorting GridView?

Question

I have an ASP .NET page with several GridView controls for which I'm implementing sorting and paging.

I'm using session variables to maintain a DataTable representing a given page of the GridView data in the ViewState like so:

protected void gv_Sorting(object sender, GridViewSortEventArgs e)
{
      // Session["Page"] represents the active page of the GridView 
      // when the Sorting event fires.
      DataTable dt = Session["Page"] as DataTable;

      if (dt != null)
      {       
           if (ViewState["SortDirection"] == null)
           {
                ViewState["SortDirection"] = "DESC";
           }

           string ViewState_SortDirection = ViewState["SortDirection"].ToString();

           for (int i = 0; i <= ((GridView)sender).Columns.Count - 1; i++)
           {
                if (e.SortExpression == ((GridView)sender).Columns[i].SortExpression)
                {
                     if (ViewState["SortDirection"].ToString() == "ASC")
                     {
                          e.SortDirection = SortDirection.Descending;
                          ((GridView)sender).Columns[i].HeaderText = ((GridView)sender).Columns[i].HeaderText + " ▼";
                          ViewState["SortDirection"] = "DESC";
                     }
                     else if (ViewState["SortDirection"].ToString() == "DESC")
                     {
                          e.SortDirection = SortDirection.Ascending;
                          ((GridView)sender).Columns[i].HeaderText = ((GridView)sender).Columns[i].HeaderText + " ▲";
                          ViewState["SortDirection"] = "ASC";
                     }
                }
           }

           DataView dv = new DataView(dt)
           {
                Sort = e.SortExpression + " " + ViewState["SortDirection"]
           };

           gv.DataSource = dv;
           gv.DataBind();

           Session["Page"] = dv.ToTable();
           DataTable dt = Session["Page"] as DataTable;
      }
 }

I'd like to have each GridView use the same Sorting event handler. When session variables in the state bag like Session["Page"] are in use, is this session variable specific to the GridView whose Sorting event fires? Or can it be modified by other GridView controls using it to sort on the same page? Meaning, if I have another GridView which also uses Session["Page"] for paging, will that session variable be in that control's scope?

Or, should I just follow the lead of this post's answer and pass only the SortDirection for each session?

Answer 1

Here are the available data-persisting variable types and their scopes:

• Application Variables (shared between all user sessions, for the entire application)
• Session Variables (shared between all pages, for the entire user session)
• ViewState Variables (exists solely on the page, for the entire page)
• ControlState Variables (exists solely on the page, just for the control)

If you are storing your grid data as Session variables, you will run into issues when you use two grids in the same page. I cannot give any specific suggestions on how to store the data without knowing more about the system, but the types of variables above may point you in the right direction