Disable Update button when reordering is not modified in GridView using jQuery Drag and Drop in ASP.Net

Here I have created sample that full-fill your requirement.

HTML

<div>
    <asp:GridView ID="gvLocations" runat="server" AutoGenerateColumns="false">
        <Columns>
            <asp:TemplateField HeaderText="Id" ItemStyle-Width="30">
                <ItemTemplate>
                    <%# Eval("Id") %>
                    <input type="hidden" name="LocationId" value='<%# Eval("Id") %>' />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField="Location" HeaderText="Location" ItemStyle-Width="150" />
            <asp:BoundField DataField="Preference" HeaderText="Preference" ItemStyle-Width="100" />
        </Columns>
    </asp:GridView>
    <br />
    <asp:Button ID="btnUpdate" Text="Update Preference" runat="server" OnClick="UpdatePreference" />
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/themes/smoothness/jquery-ui.css" />
    <script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.8.24/jquery-ui.min.js"></script>
    <script type="text/javascript">
        $(function () {
            $('[id*=btnUpdate]').attr("disabled", true);
        });
        $(function () {
            $("[id*=gvLocations]").sortable({
                items: 'tr:not(tr:first-child)',
                cursor: 'pointer',
                axis: 'y',
                dropOnEmpty: false,
                start: function (e, ui) {
                    ui.item.addClass("selected");
                },
                stop: function (e, ui) {
                    ui.item.removeClass("selected");
                    $('[id*=btnUpdate]').attr("disabled", false);
                },
                receive: function (e, ui) {
                    $(this).find("tbody").append(ui.item);
                }
            });
        });
    </script>
</div>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid()
{
    string query = "SELECT Id, Location, Preference FROM HolidayLocations ORDER BY Preference";
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand(query))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvLocations.DataSource = dt;
                    gvLocations.DataBind();
                }
            }
        }
    }
}

protected void UpdatePreference(object sender, EventArgs e)
{
    int[] locationIds = (from p in Request.Form["LocationId"].Split(',')
                            select int.Parse(p)).ToArray();
    int preference = 1;
    foreach (int locationId in locationIds)
    {
        this.UpdatePreference(locationId, preference);
        preference += 1;
    }

    Response.Redirect(Request.Url.AbsoluteUri);
}

private void UpdatePreference(int locationId, int preference)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("UPDATE HolidayLocations SET Preference = @Preference WHERE Id = @Id"))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.CommandType = CommandType.Text;
                cmd.Parameters.AddWithValue("@Id", locationId);
                cmd.Parameters.AddWithValue("@Preference", preference);
                cmd.Connection = con;
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
            }
        }
    }
}

Screenshot