get data in datagridview textbox column when item selected from datagridview combobox column

<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>

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();
    }

private void dataGridView1_EditingControlShowing(object sender,
    DataGridViewEditingControlShowingEventArgs e)
{
    ComboBox cb = e.Control as ComboBox;
    if (cb != null)
    {
        // first remove event handler to keep from attaching multiple:
        cb.SelectedIndexChanged -= new
        EventHandler(cb_SelectedIndexChanged);

        // now attach the event handler
        cb.SelectedIndexChanged += new
        EventHandler(cb_SelectedIndexChanged);
    }
}

void cb_SelectedIndexChanged(object sender, EventArgs e)
{
    MessageBox.Show("Selected index changed");
}