I haven't tested your code, but I think what's happening here is that ExcelObject is a property of your Exobj object which will contain a reference to an Excel application object. You need to initialise your properties with :

Function init
this.ExcelObject=createObject("Excel.Application")
this.ExcelObject.Visible = .F.

Function show
this.ExcelObject.visible = .T.

Best wishes,
Neil