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。