<pre>Gridview Markup
<asp:TemplateField HeaderText="Address">
<EditItemTemplate><asp:TextBox ID="txtEAddress" Width="100px" runat="server" Text='<%# Bind("Address") %>'></asp:TextBox><asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" onselectedindexchanged="DropDownList1_SelectedIndexChanged"><asp:ListItem>4</asp:ListItem><asp:ListItem>3</asp:ListItem><asp:ListItem>2</asp:ListItem><asp:ListItem>1</asp:ListItem></asp:DropDownList></EditItemTemplate><ItemTemplate><asp:Label ID="Label3" runat="server" Text='<%# Bind("Address") %>'></asp:Label></ItemTemplate><FooterTemplate><asp:TextBox ID="txtAddress" runat="server" Width="100px" TextMode="MultiLine"></asp:TextBox></FooterTemplate></asp:TemplateField>
Code Behind
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
DropDownList ddl = (DropDownList)sender;
GridViewRow row = (GridViewRow)ddl.Parent.Parent;
int idx = row.RowIndex;
TextBox txtECustCode = (TextBox)row.Cells[0].FindControl("txtECustCode");
string _text1 = txtECustCode.Text.ToString();
}