一个继承于DropDownList的树状控件

由于工作需要特扩展了一下已有的DropDownList控件，使其能显示树状结构的数据，主要用于那些有层次关系的数据显示。
如下图所示：
该控件为无限级扩展的，只需要指定其子节点字段名(默认为ID)，父节点字段名(默认为parentID)，以及第一层父节点的值即可(默认为0)。

1.首先定义常量

protected const string strT="├";
protected const string strL="└";
protected const string strI="│";
protected DataTable tempTable;
protected int lay = 0;//节点层数
protected int level=0;//DropDownList顺序

2.添加属性

属性
[Category("数据"),Description("第一层父节点的值")]
        public int FirstParentValue
        {
            get
            {
                object obj=ViewState["FirstParentValue"];
                return ((obj==null)?0:(int)obj);
            }
            set
            {
                ViewState["FirstParentValue"]=value;
            }
        }

        [Category("数据"),Description("子字段名")]
        public string ChildField
        {
            get
            {
                object obj=ViewState["ChildField"];
                return ((obj==null)?"ID":(string)obj);
            }
            set
            {
                ViewState["ChildField"]=value;
            }
        }

        [Category("数据"),Description("父字段名")]
        public string ParentField
        {
            get
            {
                object obj=ViewState["ParentField"];
                return ((obj==null)?"parentID":(string)obj);
            }
            set
            {
                ViewState["ParentField"]=value;
            }
        }

        [Category("数据"),Description("显示文本字段名")]
        public string ShowText
        {
            get
            {
                object obj=ViewState["ShowText"];
                return ((obj==null)?"name":(string)obj);
            }
            set
            {
                ViewState["ShowText"]=value;
            }
        }

3.计算当前节点所在的层以及是否为子节点，是否有兄弟节点等函数，用于生成树形

生成树形时要用的函数
/**//// <summary>
        /// 递归算出指定ID所在树中的层数
        /// </summary>
        /// <param name="treeTable"></param>
        /// <param name="ID">节点ID</param>
        private void FindLay(DataTable treeTable,int ID) 
        {
            for(int i=0;i<treeTable.Rows.Count;i++) 
            {
                if (ID == int.Parse(treeTable.Rows[i][this.ChildField].ToString()))
                {
                    int parentID = int.Parse(treeTable.Rows[i][this.ParentField].ToString());
     
                    // 如果父节点不是根节点,递归
                    if(parentID != 0) 
                    {
                        lay ++;
                        FindLay(treeTable,int.Parse(treeTable.Rows[i][this.ParentField].ToString()));
                    }
                }
            }            
        }        

        /**//// <summary>
        /// 判断是否有子接点
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="ID">当前节点的ID</param>
        /// <returns></returns>
        private bool IsExistChildNodes(DataTable dt,string ID)
        {
            bool flag=false;
            if(ID==null)
                return flag;
            for(int i=0;i<dt.Rows.Count;i++)
            {
                if(dt.Rows[i][this.ParentField].ToString()==ID)
                {
                    flag=true;
                    return flag;
                }
                else
                {
                    flag=false;
                }
            }
            return flag;
        }

        /**//// <summary>
        /// 判断是否有兄弟节点
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="ID">当前节点的ID</param>
        /// <returns></returns>
        private bool IsBorthorNodes(DataTable dt,string ID)
        {            
            bool flag=false;
            if(ID==null)
                return flag;
            for(int i=0;i<dt.Rows.Count;i++)
            {
                if(dt.Rows[i][this.ChildField].ToString()==ID&&i<dt.Rows.Count-1)
                {
                    if(dt.Rows[i][this.ParentField].ToString()==dt.Rows[i+1][this.ParentField].ToString())
                    {
                        flag=true;
                        return flag;
                    }
                    else
                    {
                        flag=false;
                        return flag;
                    }
                }              
                  
            }
            return flag;
        }
        
        /**//// <summary>
        /// 判断当前节点是否为子节点
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="ID"></param>
        /// <returns></returns>
        private bool IsChildNode(DataTable dt,string ID)
        {        
            bool flag=false;
            if(ID==null)
                return flag;
            for(int i=0;i<dt.Rows.Count;i++)
            {
                if(dt.Rows[i][this.ChildField].ToString()==ID)
                {
                    if(dt.Rows[i][this.ParentField].ToString()=="0")
                    {                      
                        flag=false;
                        return flag;
                    }
                    else
                    {
                        flag=true;
                        return flag;
                    }
                }
            }
            return flag;
        }

4.递归生成树形

递归生成树形
/**//// <summary>
        /// 数据添加并生成树形
        /// </summary>
        /// <param name="dt"></param>
        /// <param name="ID"></param>
        private void BindData(DataTable dt,string ID)
        {
            DataRow[] dr;
            dr=dt.Select(this.ParentField+"="+ID,this.ChildField+" ASC");            
            for(int x=0;x<dr.Length;x++)
            {     
                string str="";  
                lay=0;
                this.FindLay(dt,int.Parse(dr[x][this.ChildField].ToString()));
                if(this.IsChildNode(dt,dr[x][this.ChildField].ToString())==true)
                {                    
                    for(int i=0;i<lay;i++)
                    {
                        str+=strI;
                    }
                    if(this.IsBorthorNodes(dt,dr[x]["id"].ToString())==true)
                    {
                        this.Items.Insert(level,new ListItem(str+strT+dr[x][this.ShowText].ToString(),dr[x][this.ChildField].ToString()));
                    }
                    else
                    {
                     this.Items.Insert(level,new ListItem(str+strL+dr[x][this.ShowText].ToString(),dr[x][this.ChildField].ToString()));
                    }
                }
                else
                {
                    this.Items.Insert(level,new ListItem(str+dr[x][this.ShowText].ToString(),dr[x][this.ChildField].ToString()));
                }                
                level+=1;
                this.BindData(dt,dr[x][this.ChildField].ToString());//递归生成树
            }
        }

5.绑定数据

绑定数据
 /**//// <summary>
        /// 绑定数据
        /// </summary>
        /// <param name="dt">数据源DataTable</param>
        public void BindListData(DataTable dt)
        {
            tempTable=dt.Clone();
            this.BindData(dt,this.FirstParentValue.ToString());
        }

使用的时候调用该函数进行数据绑定！

请大家多多指教以便改进，谢谢！