c#中与vb中CType相同功能的函数(强类型转换)

vb:  CType(obj,TextBox)    CType(Sender,Control)
      例如 ：  Dim tb1 As TextBox = CType(e.Item.Cells(1).Controls(1), TextBox)
c#:  (TextBox)obj       
    例如 ： TextBox tb = (TextBox) e.Item.Cells[2].Controls[0]; 
           TextBox tb = (TextBox) e.Item.Cells[2].Controls.FindControl("TextBoxID");

Object o;
TextBox tb = (TextBox)o;
TextBox tb2 = o as TextBox;