Find the Checkbox checked in DevExpress Gridview

using DevExpress.web.AspxGridview;

ASPxGridView grid = (ASPxGridView)Userctrl1.FindControl("grvCertificate");
 int icnt = grid.VisibleRowCount;  //Rows count
        
DevExpress.Web.ASPxEditors.ASPxCheckBox testchk1 = (DevExpress.Web.ASPxEditors.ASPxCheckBox)grid.FindRowCellTemplateControl(VisibleIndex, null, "chkCertType");

here  VisibleIndex is integer...