Avoid (Prevent) page refresh after update ASP.Net GridView Row in C#

Sir Please help

I am trying to edit GridView row and when I click edit page ok but after click on update page is refreshing and all information goes away.

<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true" ></asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server"  UpdateMode="Conditional" >
<ContentTemplate>
    <asp:GridView ID="gvCustomers" DataKeyNames="CustomerId" runat="server" AutoGenerateColumns="false"
        OnRowEditing="EditCustomer" OnRowDataBound="RowDataBound" OnRowUpdating="UpdateCustomer" 
        OnRowCancelingEdit="CancelEdit"  >
        <Columns>
            <asp:BoundField DataField="ContactName" HeaderText="Contact Name" />
            <asp:TemplateField HeaderText="City">
                <ItemTemplate>
                    <asp:Label ID="lblCity" runat="server" Text='<%# Eval("City")%>'></asp:Label>
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:DropDownList ID="ddlCities" runat="server">
                    </asp:DropDownList>
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:CommandField ShowEditButton="True" />
        </Columns>
    </asp:GridView>
</ContentTemplate>
</asp:UpdatePanel>

public partial class CS : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!this.IsPostBack)
        {
            this.BindGrid();
        }
    }

    private void BindGrid()
    {
        string sql = "SELECT TOP 10 srNo as CustomerID, staffname as ContactName, divisionname as City FROM staffmaster";
        string conString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
        using (SqlConnection con = new SqlConnection(conString))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(sql, con))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvCustomers.DataSource = dt;
                    gvCustomers.DataBind();
                }
            }
        }
    }

    protected void EditCustomer(object sender, GridViewEditEventArgs e)
    {
        gvCustomers.EditIndex = e.NewEditIndex;
        this.BindGrid();
    }

    protected void CancelEdit(object sender, GridViewCancelEditEventArgs e)
    {
        gvCustomers.EditIndex = -1;
        this.BindGrid();
    }

    protected void RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow && gvCustomers.EditIndex == e.Row.RowIndex)
        {
            DropDownList ddlCities = (DropDownList)e.Row.FindControl("ddlCities");
            string sql = "SELECT DISTINCT divisionname as city FROM Staffmaster";
            string conString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
            using (SqlConnection con = new SqlConnection(conString))
            {
                using (SqlDataAdapter sda = new SqlDataAdapter(sql, con))
                {
                    using (DataTable dt = new DataTable())
                    {
                        sda.Fill(dt);
                        ddlCities.DataSource = dt;
                        ddlCities.DataTextField = "City";
                        ddlCities.DataValueField = "City";
                        ddlCities.DataBind();
                        string selectedCity = DataBinder.Eval(e.Row.DataItem, "City").ToString();
                        ddlCities.Items.FindByValue(selectedCity).Selected = true;
                    }
                }
            }
        }
    }

    protected void UpdateCustomer(object sender, GridViewUpdateEventArgs e)
    {
        string city = (gvCustomers.Rows[e.RowIndex].FindControl("ddlCities") as DropDownList).SelectedItem.Value;
        string customerId = gvCustomers.DataKeys[e.RowIndex].Value.ToString();
        string conString = ConfigurationManager.ConnectionStrings["conString"].ConnectionString;
        using (SqlConnection con = new SqlConnection(conString))
        {
            string query = "UPDATE StaffMaster SET DivisionName = @City WHERE SrNo = @CustomerId";
            using (SqlCommand cmd = new SqlCommand(query, con))
            {
                cmd.Parameters.AddWithValue("@CustomerId", customerId);
                cmd.Parameters.AddWithValue("@City", city);
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
                Response.Redirect(Request.Url.AbsoluteUri);
            }
        }
    }
}

Thanks

Arvind