DropDownList中如何添加2级下拉菜单

  
    

   
      
   
     if
   
      (
   
     !
   
     IsPostBack)
 {
 List
   
     <
   
     Model.categroy
   
     >
   
      list
   
     =
   
      
   
     new
   
      DAL.categroy().GetListArray(
   
     ""
   
     );
  
    
  
    

   
      //取出所有数据放入泛型list中 效率更高
 var q 
   
     =
   
      list.Where(x 
   
     =>
   
      x.pid 
   
     ==
   
      
   
     0
   
     );
  
    
  
    

   
     //linq语句 x代表list中的每一项 如果pid为0则取出放入q中
 
   
     foreach
   
      (Model.categroy item 
   
     in
   
      q)
 {
 DropDownList1.Items.Add(
   
     new
   
      ListItem(item.caname,item.id.ToString()));
  
    
  
    

   
     //父级菜单
 var q2 
   
     =
   
      list.Where(y 
   
     =>
   
      y.pid 
   
     ==
   
      item.id);
  
    
  
    

   
     
 
   
     foreach
   
      (var item2 
   
     in
   
      q2)
 {
 DropDownList1.Items.Add(
   
     new
   
      ListItem(
   
     "
   
     ......
   
     "
   
      
   
     +
   
      item2.caname, item2.id.ToString()));
//二级菜单
 
 }
 }
 }