GridView中的错误

我把代码写在按钮下面,如下

 string actkey = string.Empty;
    foreach (GridViewRow row in GridView1.Rows)
    {
        //Label lbInvoice = (Label)row.FindControl("lblInvoice");
        string strInvoice = GridView1.DataKeys[row.RowIndex].Values["lblInvoice"].ToString();
        objinvoice.Invoice = strInvoice;
        RadioButton rdn = (RadioButton)row.FindControl("rdnRenew");
        if (rdn.Checked)
        {
            actkey = oCustomerDetails.CreateRandom(20);
            objinvoice.activationcode = actkey;
            objinvoice.editInvoice(actkey, strInvoice);
        }
    }

但我在这个问题上犯了一个错误

string strInvoice = GridView1.DataKeys[row.RowIndex].Values["lblInvoice"].ToString();

我写的东西有什么问题吗

我声明我的项目模板如下

      <ItemTemplate>
                        <asp:Label ID="lblInvoice" runat="server" Text='<%# Eval("invoceNo") %>'></asp:Label>
                    </ItemTemplate>