DataGrid.Select edIndex is always -1

[js]

I have a DataGrid with a command button on the first column of the
DataGrid. The DataGrid is databound to a dataset with DataKeyFiled
bound to "ControlNum ber" field in the dataset. I am trying to save the
row's ControlNumber to a page level variable when the corresponding
item command is clicked . However, no matter what I do, the page
property is alway blank.

I also tried use CheckBox in the ItemTemplate. The CheckBox's
AutoPostBack is set to false. Another Command button outside the
DataGrid is used do the postback. Strangely, even I have one box
checked, upon post back the SelectedIndex is always -1.

Does anyone know how to save the "ControlNum ber" to the page variable
strControlNumbe r? Thanks.

The following is the event handler for the DataGrid's OnItemCommand
event.

////////// CodeBehind partial content /////////
public class CustomPaging : System.Web.UI.P age
protected string strControlNumbe r;
public string ControlNumber
{
get
{
if (strControlNumb er == null)
return "no value";
else
return strControlNumbe r;
}
}
private void MyDataGrid_Item Command(object source,
System.Web.UI.W ebControls.Data GridCommandEven tArgs e)
{
TableCell CellControlNumb er = e.Item.Cells[1];
strControlNumbe r = CellControlNumb er.Text;
Server.Transfer ("inventory.asp x");
}

private void btnConfirmSelec tion_Click(obje ct sender, System.EventArg s
e)
{
strControlNumbe r = MyDataGrid.Sele ctedIndex.ToStr ing();
Server.Transfer ("inventory.asp x");
}

/////////// ASPX partial content /////////
<asp:button id="btnConfirmS election" runat="server" Text="Confirm
Selection"/>
<asp:datagrid id="MyDataGrid " runat="server" CssClass="Inven toryTable"
AutoGenerateCol umns="False"
AllowSorting="T rue">
<Columns>
<asp:TemplateCo lumn>
<ItemTemplate >
<asp:Checkbox ID="chkSelected " Runat="server"/>
<asp:Button Text="Select" runat="server" />
</ItemTemplate>
</asp:TemplateCol umn>
<asp:TemplateCo lumn>
<HeaderTemplate >Control<br />Number</HeaderTemplate>
<ItemTemplate >
<%# DataBinder.Eval (Container.Data Item, "ControlNumber" ) %>
</ItemTemplate>
</asp:TemplateCol umn>
</Columns>
</asp:datagrid>