using FindControl to capture programitacialy created dropdown list

[tagg3rx]

Hi All,
I have created a panel as a place holder on an input interface and I want to be able to dynamicaly fill it with drop down lists, check boxes etc. So below I'll show you the two main pieces of this effort - the function that creates the dropdown list in question and the function that fires when the submit button is clicked.
I've stepped through this and what I'm finding is that when the submit button is clicked the page posts back and the dropdown list is removed from the page.

    protected void lbNewShiftLog_Click(object sender, EventArgs e)
    {
        DropDownList ddlCusts = new DropDownList();
               //datasource is populating the dropdown list fine
        ddlCusts.DataSource = dS;
        ddlCusts.DataTextField = "customer";
        ddlCusts.DataValueField = "customer";
        ddlCusts.DataBind();
        ddlcusts.ID = "ddlcusts";
        pnlOptions.Controls.Add(ddlcusts);
    }
 
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
    DropDownList ddl = (DropDownList)pnlOptions.FindControl("ddlCusts");
    if (ddl != null)
      {
       Label1.Text = ddl.SelectedItem.ToString();
      }
    }
 

-----------------------------------------------------------------------
The above function returns null - I have also tried

DropDownList ddl = (DropDownList)PreviousPage.FindControl("ddlCusts");
 

Which returns the error:
Object reference not set to an instance of an object.

Plz Healp
Thank You

[Plater]

Well, it might me just a copy/paste error, but the ID is all lowercase, and then in your search string it's got a capital letter?

[tagg3rx]

Hi Thanks for the response
I fixed that and I'm still getting the same thing.

What is the cause of this error when i'm using the previouspage namespace

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:


Line 67: case "NewLog":
Line 68: //FindControl
Line 69: DropDownList ddl = (DropDownList)PreviousPage.FindControl("ddlCusts") ;
Line 70: if (ddl != null)
Line 71: {


Source File: c:\Documents and Settings\dlewis\My Documents\Visual Studio Codename Orcas\WebSites\Log\Default.aspx.cs Line: 69

[TRScheel]

Hi Thanks for the response
I fixed that and I'm still getting the same thing.

What is the cause of this error when i'm using the previouspage namespace

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:


Line 67: case "NewLog":
Line 68: //FindControl
Line 69: DropDownList ddl = (DropDownList)PreviousPage.FindControl("ddlCusts") ;
Line 70: if (ddl != null)
Line 71: {


Source File: c:\Documents and Settings\dlewis\My Documents\Visual Studio Codename Orcas\WebSites\Log\Default.aspx.cs Line: 69

Did you check to make sure that PreviousPage isnt null? Or can be cast to DropDownList?

[tagg3rx]

Ok yea thats not going to work I just read up on previous page and realized its only for non postback operations, when i tried to set it I got "Circular file references are not allowed."

So the issue is when the script runs the dropdown list is no longer there, why is it disapearing, I dont have any code telling pnlOptions to purge or reset it's self. nor is there any code that i can tell that fires between the dropdown list being created and when the submit code runs???

[TRScheel]

Ok yea thats not going to work I just read up on previous page and realized its only for non postback operations, when i tried to set it I got "Circular file references are not allowed."

So the issue is when the script runs the dropdown list is no longer there, why is it disapearing, I dont have any code telling pnlOptions to purge or reset it's self. nor is there any code that i can tell that fires between the dropdown list being created and when the submit code runs???

To be honest am surprised that with the code you provided the dynamic DDL stays after a post back.

You mind posting all or a good chunk of your code for that page? (Or and place it within code tags).

[tagg3rx]

Ok I did a break out of how I have written it thus far (agian I appriciate your help I'm still learning the fundamentals here)

Heres what I got :

default.aspx

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>
 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
 
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
        <asp:Panel ID="Panel1" runat="server" Height="50px" Width="125px">
            <asp:Button ID="btnSubmit" runat="server" Text="Submit" 
            onclick="btnSubmit_Click" />
        </asp:Panel>
        <asp:Button ID="btnCreate" runat="server" Text="Create" 
        onclick="btnCreate_Click" />
    </div>
    </form>
</body>
</html>
 

default.aspx.cs

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;
 
public partial class _Default : System.Web.UI.Page 
{
    public string csNetops = "server=****;" +
    "User ID=****;Password=****; database=OpsR3";
 
    protected void Page_Load(object sender, EventArgs e)
    {
 
    }
    protected void btnCreate_Click(object sender, EventArgs e)
    {
        string sqlQuery = "SELECT customer FROM NOC_Customers";
        SqlDataAdapter dA = new SqlDataAdapter(sqlQuery, csNetops);
        DataSet dS = new DataSet();
        dA.Fill(dS, "customers");
 
        DropDownList ddlCusts = new DropDownList();
        ddlCusts.DataSource = dS;
        ddlCusts.DataTextField = "customer";
        ddlCusts.DataValueField = "customer";
        ddlCusts.DataBind();
        ddlCusts.ID = "ddlCusts";
 
        Panel1.Controls.Add(ddlCusts);
 
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        DropDownList ddl = (DropDownList)Panel1.FindControl("ddlCusts");
        if (ddl != null)
            Label1.Text = ddl.SelectedItem.ToString();
        else
            Label1.Text = "Failed";
    }
}
 
 
 

[tagg3rx]

Ahh I figured out what I was doing wron - I was over thinking the issue.

I replaced the findcontrol with:

string cust = Request.Form["ddlCusts"];

And now all is well....

All this fancy oop coding I've been learning with .net made me forget about the data in the post....

DOH!

[Frinavale]

Ahh I figured out what I was doing wron - I was over thinking the issue.

I replaced the findcontrol with:

string cust = Request.Form["ddlCusts"];

And now all is well....

All this fancy oop coding I've been learning with .net made me forget about the data in the post....

DOH!

Good stuff!

Thanks for sharing the solution.

-Frinny