一款层次下拉列表控件

     在项目中经常遇到树状结构的对象比如产品分类、部门结构、地区……对于这类对象的呈现，一般都使用树控件（比如VS2005自带的TreeView控件）。但是树控件的使用和操作都比较复杂，对于一些比较简单的操作，比如单选其中的一个节点的情况则可用使用下拉列表框来代替。要在DropDownList中展示出树结构的层次，那就必须在每个节点的Text前加入一定的占位符，以实现层次的效果，由于这种下拉列表控件在项目中经常使用，于是决定写一个通用的服务器控件出来。该控件继承自DropDownList，在使用中只需要为该控件设置用于数据绑定的DataTextField和DataValueField，以及新增的属性ChildProperty（string，对象的Child属性的名字）和DeepChar（string，在表示层次中使用的占位符，默认是“--”），设置了这4个属性后，在后台就只需要将树结构对象的Root节点作为DataSource，然后执行DataBind()即可。

using System;  using System.Collections.Generic;  using System.Collections;  using System.ComponentModel;  using System.Linq;  using System.Text;  using System.Web;  using System.Web.UI;  using System.Web.UI.WebControls;    namespace ServerControls   {      [ToolboxData("<{0}:DropDownTreeList runat=server></{0}:DropDownTreeList>")]      public class DropDownTreeList : DropDownList       {          private object dataSource;          private int deep = 0;             #region ----重写----          public override object DataSource           {              get               {                  return this.dataSource;              }              set               {                  this.dataSource = value;              }          }          public override void DataBind()           {              if (ChildProperty == null)               {                  throw new Exception("ChildProperty参数必须设置");              }              this.Items.Clear();              ListItemCollection items=ConvertTreeToList(dataSource);              foreach (ListItem item in items)               {                  this.Items.Add(item);              }            }          #endregion             #region ----私有方法----          private ListItemCollection ConvertTreeToList(object root)           {              deep = 0;              ListItemCollection list =  new ListItemCollection();              list.Add(GetListItem(root));              ConvertTree(list, root);              return list;          }           /// <summary>          /// 将对象转换为ListItem          /// </summary>          /// <param name="root"></param>          /// <returns></returns>          private ListItem GetListItem(object root)           {              ListItem item = new ListItem();              item.Text =GetDeepChar()+ root.GetType().GetProperty(this.DataTextField).GetValue(root, null).ToString();              item.Value = root.GetType().GetProperty(this.DataValueField).GetValue(root, null).ToString();              return item;          }          private void ConvertTree(ListItemCollection list, object root)           {              object childs= root.GetType().GetProperty(this.ChildProperty).GetValue(root,null);//获得Child的集合              if(childs==null)               {                  return;              }              if(!(childs is ICollection))               {                  throw new Exception("数据源的"+ChildProperty+"属性必须实现ICollection接口");              }              deep++;              foreach(object child in (ICollection)childs)               {                    list.Add(GetListItem(child));                  ConvertTree(list, child);//递归转换下一层节点              }              deep--;          }           /// <summary>          /// 根据节点的深度返回节点前的占位字符          /// </summary>          /// <returns></returns>          private string GetDeepChar()           {              string str = "";              for (int i = 0; i < deep; i++)               {                  str += DeepChar;              }              return str;            }          #endregion           #region ----公开的属性----          [Description("表示深度增加的字符")]          public string DeepChar           {              get               {                  if (ViewState["DeepChar"] == null || ViewState["DeepChar"].ToString()=="")                   {                      return "--";                  }                  return ViewState["DeepChar"].ToString();              }               set { ViewState["DeepChar"] = value; }          }          [Description("对象的子节点集合属性名")]          public string ChildProperty           {              get               {                  if (ViewState["ChildProperty"] == null)                   {                      return null;                  }                  return ViewState["ChildProperty"].ToString();              }               set { ViewState["ChildProperty"] = value; }          }          #endregion      }  }   具体调用示例： 1，将该控件添加到aspx页面中并设置必要的属性。  <cc1:DropDownTreeList ID="DropDownTreeList1" runat="server"                  ChildProperty="ChildArea" DataTextField="Name" DataValueField="Code"                  DeepChar="--"> 2，在页面的后台代码中添加数据源并进行数据绑定。    public partial class _Default : System.Web.UI.Page   {      protected void Page_Load(object sender, EventArgs e)       {          this.DropDownTreeList1.DataSource = InitArea();          this.DropDownTreeList1.DataBind();      }        private Area InitArea()       {           Area area1 = new Area { Code = 1, Name = "中国" };           Area area2 = new Area { Code = 2, Name = "四川" };           Area area3 = new Area { Code = 3, Name = "北京" };           Area area4 = new Area { Code = 4, Name = "广东" };           Area area5 = new Area { Code = 5, Name = "成都" };           Area area6 = new Area { Code = 6, Name = "乐山" };           Area area7 = new Area { Code = 7, Name = "绵阳" };           Area area8 = new Area { Code = 8, Name = "广州" };           Area area9 = new Area { Code = 9, Name = "深圳" };           Area area10 = new Area { Code = 10, Name = "东莞" };           Area area11 = new Area { Code = 11, Name = "珠江" };             area1.ChildArea = new List<Area> { area2, area3, area4 };           area2.ChildArea = new List<Area> { area5, area6, area7 };           area4.ChildArea = new List<Area> { area9, area10, area11 };          return area1;      }  }  public class Area   {       public string Name { get; set; }       public int Code { get; set; }       public List<Area> ChildArea { get; set; }  } 这个控件目前我发现的一个问题就是我将DataBind方法完全重写了，所以控件的DataTextFormatString失效了，由于很少使用这个属性，所以一般不影响使用。