private void GetCtrl()
        {
            System.Web.UI.HtmlControls.HtmlInputControl datepickerControl = this.FindControl("chkAll") as System.Web.UI.HtmlControls.HtmlInputControl;

            //Get String Value
            string getValue = datepickerControl.Value;
            //Get bool Value
            bool getChecked = ((System.Web.UI.HtmlControls.HtmlInputCheckBox)(datepickerControl)).Checked;
        }
 protected void gvPaymentAssimilate_RowDataBound(object sender, GridViewRowEventArgs e)
 {
     if (e.Row.RowType == DataControlRowType.DataRow)
     {
         System.Web.UI.HtmlControls.HtmlInputControl headerchk = this.FindControl("chkAll") as System.Web.UI.HtmlControls.HtmlInputControl;
         // CheckBox headerchk = (CheckBox)gvPaymentAssimilate.HeaderRow.FindControl("chkheader");
         CheckBox childchk = (CheckBox)e.Row.FindControl("chkchild");
         childchk.Attributes.Add("onclick", "javascript:Selectchildcheckboxes('" + headerchk.ClientID + "')");
     }
 }