i design program "Library Management"i want to design 3 levels with VB.Net.I designed cussessfull. The First level is SQL class(contain Database SQL).The second level is INTERFACE(contain objects. For exsample, Button,DataGrid,ComboBox..).The third level is CONTROLER(contain class,function...).i want to declare ComboBox in class CONTROLER sothat using.Help me please.....