DropDownList捆绑分类无法显示的错误，高手请教

Question

前台：
<asp:DropDownList ID="DdlSort" runat="server" Width="160px"></asp:DropDownList>后台
protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack){  BindDropdownList();  }
    }
    public DataTable ExecuteDataTable(string CommandTxt)
    {
        string ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + HttpContext.Current.Server.MapPath(System.Configuration.ConfigurationManager.AppSettings["Data"]);
        OleDbConnection Conn = new OleDbConnection(ConnectionString);
        DataTable dataTable = new DataTable();
        OleDbDataAdapter adapter = new OleDbDataAdapter(CommandTxt, Conn);
        {
            adapter.Fill(dataTable);
        }
        return dataTable;
    }
    protected void BindDropdownList()
    {
        DataTable dt = new DataTable();
        try
        {
            dt = ExecuteDataTable("Select * from ClassInfo");
            CreateLevelDropDown(this.DdlSort, dt);
        }
        catch (Exception) { }
    }
    private void CreateLevelDropDown(DropDownList ddlst, DataTable dt)
    {
        System.Collections.ArrayList allItems = new ArrayList();
        DataRow[] rows = dt.Select("ClassPID=" + 0);
        foreach (DataRow row in rows)
        {
            CreateLevelDropDownAssistant(dt, ref allItems, row, string.Empty);
        }
        ListItem[] items = new ListItem[allItems.Count];
        allItems.CopyTo(items);
        ddlst.Items.AddRange(items);
    }
    private void CreateLevelDropDownAssistant(DataTable dt, ref ArrayList items, DataRow parentRow, string curHeader)
    {
        ListItem newItem = new ListItem(curHeader + parentRow["ClassName"].ToString(), parentRow["ClassID"].ToString());
        items.Add(newItem);
        parentRow.Delete();
        DataRow[] rows = dt.Select("ClassPID='" + newItem.Value + "'");
        for (int i = 0; i < rows.Length - 1; i++)
        {
            CreateLevelDropDownAssistant(dt, ref items, rows[i], curHeader.Replace("┣", "┃").Replace("┗", "┣") + "┣");
        }
        if (rows.Length > 0)
        {
            CreateLevelDropDownAssistant(dt, ref items, rows[rows.Length - 1], curHeader.Replace("┣", "┃").Replace("┗", "┣") + "┗");
        }
    }数据库设计ClassID ClassPID ClassName为什么我始终绑定不了数据？？？？？？？？？？

Answer 1

you need call DataBind() as below.  private   void   CreateLevelDropDown(DropDownList   ddlst,   DataTable   dt) 
        { 
                System.Collections.ArrayList   allItems   =   new   ArrayList(); 
                DataRow[]   rows   =   dt.Select("ClassPID="   +   0); 
                foreach   (DataRow   row   in   rows) 
                { 
                        CreateLevelDropDownAssistant(dt,   ref   allItems,   row,   string.Empty); 
                } 
                ListItem[]   items   =   new   ListItem[allItems.Count]; 
                allItems.CopyTo(items); 
                ddlst.Items.AddRange(items); 
                ddlst.DataBind();
        } 

Answer 2

protected   void   Page_Load(object   sender,   EventArgs   e) 
        { 
                if   (!IsPostBack){     BindDropdownList();     } 
        } 
        public   DataTable   ExecuteDataTable(string   CommandTxt) 
        { 
                string   ConnectionString   =   "Provider=Microsoft.Jet.OLEDB.4.0;Data   Source="   +   HttpContext.Current.Server.MapPath(System.Configuration.ConfigurationManager.AppSettings["Data"]); 
                OleDbConnection   Conn   =   new   OleDbConnection(ConnectionString); 
                DataTable   dataTable   =   new   DataTable(); 
                OleDbDataAdapter   adapter   =   new   OleDbDataAdapter(CommandTxt,   Conn); 
                { 
                        adapter.Fill(dataTable); 
                } 
                return   dataTable; 
        } 
        protected   void   BindDropdownList() 
        { 
                DataTable   dt   =   new   DataTable(); 
                try 
                { 
                        dt   =   ExecuteDataTable("Select   *   from   ClassInfo"); 
                        CreateLevelDropDown(this.DdlSort,   dt); 
                } 
                catch   (Exception)   {   } 
        } 
问题出现在这里，，，下面的问题没有，始终找不到原因

Answer 3

你是指無法把撈出來的數據綁定到dropdownlist嗎？  
在你的CreateLevelDropDown 試試
private   void   CreateLevelDropDown(DropDownList   ddlst,   DataTable   dt) 
{ 
        ddlst.DataSource = dt;
        ddlst.DataValueField = dt.Columns["DATA0"].ToString();//要給ddlst的value集合
        ddlst.DataTextField = dt.Columns["DATA1"].ToString();//要給ddlst的text（顯示）集合
        ddlst.DataBind();
} 

Answer 4

you don't have to pass this.DdlSort into CreateLevelDropDown(). If you really have to, you need use 'ref' keyword CreateLevelDropDown(ref DropDownList ddlst, DataTable   dt) protected   void   BindDropdownList() 
        { 
                DataTable   dt   =   new   DataTable(); 
                try 
                { 
                        dt   =   ExecuteDataTable("Select   *   from   ClassInfo"); 
                        CreateLevelDropDown(dt); 
                } 
                catch   (Exception)   {   } 
        } 
        private   void   CreateLevelDropDown(DataTable   dt) 
        { 
                System.Collections.ArrayList   allItems   =   new   ArrayList(); 
                DataRow[]   rows   =   dt.Select("ClassPID="   +   0); 
                foreach   (DataRow   row   in   rows) 
                { 
                        CreateLevelDropDownAssistant(dt,   ref   allItems,   row,   string.Empty); 
                } 
                ListItem[]   items   =   new   ListItem[allItems.Count]; 
                allItems.CopyTo(items); 
                this.DdlSort.Items.AddRange(items); 
                this.DdlSort..DataBind(); 
        }