Avoid double click on textbox in gridview

Aspx Page looks like below


 <form id="form1" runat="server">
    <asp:scriptmanager runat="server" xmlns:asp="#unknown">
    </asp:scriptmanager>
    <asp:updatepanel runat="server" xmlns:asp="#unknown">
        <contenttemplate>
            <asp:gridview id="grdResult" runat="server" autogeneratecolumns="false">
                <columns>
                    <asp:templatefield headertext="Length">
                        <itemtemplate>
                            <asp:textbox id="TxtLength" runat="server" text="<%#Bind("Length") %>" ontextchanged="TxtLength_TextChanged">
                                        AutoPostBack="true"></asp:textbox>
                        </itemtemplate>
                    </asp:templatefield>
                    <asp:templatefield headertext="Width">
                        <itemtemplate>
                                    <asp:textbox id="TxtWidth" runat="server" text="<%#Bind("Width") %>" ontextchanged="TxtWidth_TextChanged">
                                        AutoPostBack="true"></asp:textbox>
                        </itemtemplate>
                    </asp:templatefield>
                    <asp:templatefield headertext="Area">
                        <itemtemplate>
                            <asp:textbox id="TxtArea" runat="server" text="<%#Bind("Area") %>" ontextchanged="TxtArea_TextChanged">
                                        AutoPostBack="true"></asp:textbox>
                        </itemtemplate>
                    </asp:templatefield>
                </columns>
            </asp:gridview>
        </contenttemplate>
    </asp:updatepanel>
    </form>


code behind page looks like below

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                DataTable dt = new DataTable();
                dt.Columns.Add("Length", typeof(Double));
                dt.Columns.Add("Width", typeof(Double));
                dt.Columns.Add("Area", typeof(Double));


                for (int i = 0; i < 10; i++)
                {
                    DataRow dr = dt.NewRow();

                    dr["Length"] = 1;
                    dr["Width"] = 1;
                    dr["Area"] = 1;
                    dt.Rows.Add(dr);
                }


                grdResult.DataSource = dt;
                grdResult.DataBind();
            }
        }

        protected void TxtLength_TextChanged(object sender, EventArgs e)
        {

        }
        protected void TxtWidth_TextChanged(object sender, EventArgs e)
        {

        }
        protected void TxtArea_TextChanged(object sender, EventArgs e)
        {

        }