Forms Data Controls :: Grid View Control Paging With Dropdown

I am using grid view control with paging Like-:

protected
void grdUpdateColumn_RowCreated(object
sender, GridViewRowEventArgs
e)
{

if (e.Row.RowType ==
DataControlRowType.Pager)
{
DropDownList ddl
= new
DropDownList();
//adds variants of pager size
ddl.Items.Add(
"5"
);
ddl.Items.Add(
"10"
);
ddl.Items.Add(
"20"
);
ddl.Items.Add(
"50");
ddl.AutoPostBack = true;
//selects item due to the GridView current page size

ListItem
li = ddl.Items.FindByText(grdUpdateColumn.PageSize.ToString());
if (li !=
null
)
ddl.SelectedIndex = ddl.Items.IndexOf(li);
ddl.SelectedIndexChanged +=
new
EventHandler(ddl_SelectedIndexChanged);
//adds dropdownlist in the additional cell to the pager table
Table pagerTable = e.Row.FindControl("pagerTable")as
Table;
//e.Row.Cells[0].Controls[0] as Table;
TableCell cell =
new
TableCell
();
cell.Style[
"padding-left"] =
"15px"
;
cell.Controls.Add(
new
LiteralControl("Page
Size:"
));
}
protected
void ddl_SelectedIndexChanged(object
sender, EventArgs
e)
{
//changes page size
grdUpdateColumn.PageSize = int.Parse(((DropDownList)sender).SelectedValue);
ViewState["Index"]
= 1;
//binds data source
this.GetChangesRecord();
}
Grid view Like -:
<PagerTemplate>
<asp:Table
ID="pagerTable"
runat="server"><asp:TableRow>
</asp:TableRow>

It's working fine but problem is that if i select 10 and record from dropdown and record also has 10 then paging is not showing.

That's mean i select 10 from dropdown and record is 10 then dropdown also disable with numbers, suppose i need to select again 5 then i can't do this.