如何以编程方式创建和填充下拉列表

Question

我试图使用这样的for循环创建下拉列表：

    private void Page_Load(object sender, System.EventArgs e)
    {
        //build placeholder
        for(int x = 0; x <= 10; x++) {

            DropDownList dp = new DropDownList();
            dp.ID = "carrirerDp " + x.ToString();
            dp.DataSource = PhoneCarrierSqlDataSource;               
            dp.DataTextField = "carrier_name";
            dp.DataValueField = "crr_id";
            DropDownPlaceHolder.Controls.Add(dp);
            DropDownPlaceHolder.Controls.Add(new LiteralControl("<br>"));
        }     
    } 

已创建下拉列表但它们为空。 执行我用asp标记创建的那个

 <asp:DropDownList ID="PhoneCarrierDropDownList" runat="server" 
    DataSourceID="PhoneCarrierSqlDataSource" DataTextField="carrier_name" 
    DataValueField="crr_id">
 </asp:DropDownList>  

 <asp:SqlDataSource ID="PhoneCarrierSqlDataSource" runat="server" 
    ConnectionString="<%$ ConnectionStrings:ApplicationServices %>" 
    SelectCommand="SELECT * 
                   FROM Table">
 </asp:SqlDataSource>

这是占位符：

 <asp:PlaceHolder id="Area1" runat="server"></asp:PlaceHolder>

Answer 1

你还没有数据包：

 dp.DataBind();