How to add an event handler to control inside the same event handler?

Question

I have 2 Dropdownlists with 7 textboxes in one line in AJAX update Panel; i need to create a new line of controls on each time i select an item in the second dropdownlist; and add the same eventhandler to the new created second dropdownlist..etc.

the problem is not in the first line ddl because its in HTML; but when i select a new item in the created new line ddl, the onSelectedIndexChanged does not fire, and the second line disappears!!

Any suggestions??

My HTML Code:

  <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> 

Code behind:

 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

I believe The problem is that when the second dynamically generated ddl postsback, there is no way to remember what were the dynamically rendered controls in the previous step.

I suggest you go through this article ; I think you miss the final step, ie the RecreateControls function in the aforementioned link.

Hope that helps.