如何在同一事件处理程序中添加事件处理程序以进行控制？

Question

我在AJAX更新面板中的一行中有2个Dropdownlists，其中有7个文本框； 每当我在第二个下拉列表中选择一个项目时，就需要创建新的控件行； 并将相同的事件处理程序添加到新创建的第二个下拉列表中。

问题不在第一行ddl中，因为它在HTML中； 但是当我在创建的新行ddl中选择一个新项目时，onSelectedIndexChanged不会触发，第二行消失！

有什么建议么？？

我的HTML代码：

  <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <asp:DropDownList runat="server" ID="DropDownList1" CssClass="dropdownlist" EnableViewState="true"> <asp:ListItem>a</asp:ListItem> <asp:ListItem>b</asp:ListItem> </asp:DropDownList> &nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp <asp:DropDownList runat="server" ID="DropDownList2" CssClass="dropdownlist" AutoPostBack="true" OnSelectedIndexChanged="DropDownList2_SelectedIndexChanged" EnableViewState="true"> <asp:ListItem>a</asp:ListItem> <asp:ListItem>b</asp:ListItem> </asp:DropDownList> &nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox1" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox2" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox3" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox4" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox5" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox6" CssClass="txtbx"></asp:TextBox> &nbsp&nbsp&nbsp <asp:TextBox runat="server" ID="textbox7" CssClass="txtbx"></asp:TextBox> <br /> <br /> </ContentTemplate> </asp:UpdatePanel> 

后面的代码：

 public partial class WebForm1 : System.Web.UI.Page
{
    DropDownList ddl1;
    DropDownList ddl2;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Session["ddlcounter"] = 1;
        }
    }

    protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
    {
        ddl1 = new DropDownList();
        ddl1.ID = "ddl1_" + (int)Session["ddlcounter"];
        ddl1.Width = 200;
        ddl1.Height = 30;
        ddl1.Items.Add("a");
        ddl1.Items.Add("b");
        UpdatePanel1.ContentTemplateContainer.Controls.Add(ddl1);
        UpdatePanel1.ContentTemplateContainer.Controls.Add(new LiteralControl("&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp"));

        ddl2 = new DropDownList();
        ddl2.ID = "ddl2_" + (int)Session["ddlcounter"];
        ddl2.Width = 200;
        ddl2.Height = 30;
        ddl2.Items.Add("a");
        ddl2.Items.Add("b");
        ddl2.AutoPostBack = true;
        UpdatePanel1.ContentTemplateContainer.Controls.Add(ddl2);
        UpdatePanel1.ContentTemplateContainer.Controls.Add(new LiteralControl("&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp&nbsp"));

        ddl2.SelectedIndexChanged += new EventHandler(DropDownList2_SelectedIndexChanged);

        Session["txtcounter"] = 1;
        for (int i = 0; i < 7; i++)
        {
            TextBox txt = new TextBox();
            txt.Width = 45;
            txt.Height = 25;
            UpdatePanel1.ContentTemplateContainer.Controls.Add(txt);
            UpdatePanel1.ContentTemplateContainer.Controls.Add(new LiteralControl("&nbsp&nbsp&nbsp&nbsp&nbsp"));
            Session["txtcounter"] = (int)Session["txtcounter"] + 1;
        }
        UpdatePanel1.ContentTemplateContainer.Controls.Add(new LiteralControl("<br /><br />"));
        Session["ddlcounter"] = (int)Session["ddlcounter"] + 1;
    }
}

Answer 1

我相信问题在于，当第二个动态生成的ddl回发时，无法记住上一步中动态呈现的控件。

我建议你阅读这篇文章 ； 我认为您错过了最后一步，即上述链接中的RecreateControls函数。

希望能有所帮助。