问如何为我的VSTO插件应用3层架构？

EN

private void Bt1_Click(object sender, Microsoft.Office.Tools.Ribbon.RibbonControlEventArgs e)
    {
        ObjectManager objManager = new ObjectManager(new ExcelObjectDal());
        var allObjects = objManager.GetObjects();
        //Add all objects to WinForm
    }

public class ObjectManager : IObjectService
{
    public IObjectDal ObjectDal { get; set; }
    public ObjectManager(IObjectDal DAL)
    {
        ObjectDal = DAL;
    }

    public List<Object> GetObjects()
    {
        Worksheet sheet = ObjectDal.GetObjects();
        //Business logic to extract each object from the sheet
        return new List<object>();
    }
}

public class ExcelObjectDal : IObjectDal
{
    private Workbook book;
    public ExcelObjectDal()
    {
        this.book = Globals.Factory.GetVstoObject(Globals.ThisAddIn.Application.ActiveWorkbook);
    }
    public Worksheet GetObjects()
    {
        Worksheet sheet = (Worksheet)Globals.Factory.GetVstoObject(book.Worksheets[name]);
        return sheet;
    }
}