how to do gridview sorting without data Source? - asp.net

Question

i am trying to do sorting and paging for my gridview without datasource but when i click on the header of the gridview to sort it , nothing happen but when i click for paging is working fine and there is no error. how to do about it?
this is my code:
protected void Page_Load(object sender, EventArgs e)
{
dbBind();
}
protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
{
DataTable dtSortTable = GridView1.DataSource as DataTable;
if (dtSortTable != null)
{
DataView dvSortedView = new DataView(dtSortTable);
dvSortedView.Sort = e.SortExpression + " " + getSortDirectionString(e.SortDirection);
GridView1.DataSource = dvSortedView;
GridView1.DataBind();
}
}
private string getSortDirectionString(SortDirection sortDirection)
{
string newSortDirection = String.Empty;
if(sortDirection== SortDirection.Ascending)
{
newSortDirection = "ASC";
}
else
{
newSortDirection = "DESC";
}
return newSortDirection;
}
private void dbBind()
{
DataSet ds;
string startdate = (string)(Session["startdate"]);
string enddate = (string)(Session["enddate"]);
var format = "dd/MM/yyyy";
DateTime one = DateTime.ParseExact(startdate, format, CultureInfo.InvariantCulture);
DateTime two = DateTime.ParseExact(enddate, format, CultureInfo.InvariantCulture);
if (two >= one)
{
SqlConnection conn = new SqlConnection("Data Source=localhost;Initial Catalog=n;Integrated Security=True");
//conn.Open();
SqlCommand cmd = new SqlCommand("SELECT [AmountSpent], [TimeDate]=convert(nvarchar,timedate,103), [StallNo] FROM [StudentTransactions] WHERE TimeDate BETWEEN #one AND #two", conn);
cmd.Parameters.AddWithValue("#one", one);
cmd.Parameters.AddWithValue("#two", two);
ds = new DataSet();
using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
{
sda.Fill(ds);
if (ds.Tables.Count > 0)
{
DataView dv = ds.Tables[0].DefaultView;
if (ViewState["SortDirection"] != null)
{
sortDirection = ViewState["SortDirection"].ToString();
}
if (ViewState["SortExpression"] != null)
{
sortExpression = ViewState["SortExpression"].ToString();
dv.Sort = string.Concat(sortExpression, " ", sortDirection);
}
GridView1.DataSource = dv;
GridView1.DataBind();
}
}
//GridView1.DataBind();
//conn.Close();
}
else
{
GridView1.Visible = false;
string strMsg = " Data not found for the choosen dates.";
Response.Write("<script>alert('" + strMsg + "')</script>");
}
}