Forms Data Controls :: Summing A Row In A Grid?

I can't get the total from the row of the grid as I enter in the cells of the first row. Doesn't SelectedIndexChanged fire asI leave each cell?

I set a break point in the code and it's not stopping there.

<asp:GridView ID="GrdDynamic" runat="server" AutoGenerateColumns="False"
onrowdatabound="GrdDynamic_RowDataBound"
onrowediting="GrdDynamic_RowEditing"
onselectedindexchanged="GrdDynamic_SelectedIndexChanged" SelectedIndex="1"
AutoPostBack="True">
</asp:GridView>
protected void GrdDynamic_SelectedIndexChanged(object sender, EventArgs e)
{
double total = 0;
for (int colIndex = 0; colIndex < 16; colIndex++)
{
if (GrdDynamic.Rows[0].Cells[colIndex].Text != "")
total += Convert.ToDouble(GrdDynamic.Rows[0].Cells[colIndex].Text);
}
GrdDynamic.Rows[0].Cells[16].Text = total.ToString();
}