单列方式（data与business交互）

public class CommentsBusiness   //Business{    #region 单列模式    private static CommentBusiness instance;    private CommentData dal;//Data    private CommentsBusiness()    {         dal=new CommentData();    }    public static CommentBusiness GetInstance()    {         if(instance==null)             instance=new CommentBusiness();         return instance;    }      #endregion}