Develop Reference

Recreating many dynamic controls in ASP NET (individually actions)

I have problem with ASP.NET and dynamic controls. I have three ASCX. One of them creates two textboxes and some labels. The second containing control created if first ASCX (two textboxes and some labels). In addiction, second control also have link button named “Add Next” which on click event adding another control (two textboxes and some labels). The third ASCX control contains many the second ASCX (amount depend on SQL result). I made simple image to clarify:
The orange box contains many controls. The red box adding many black boxes on click “ADD NEXT”.
For now I use session variable to save state during recreate. For one “red box” it is working, but if I add more “red boxes”, clicking every “ADD NEXT” adding new control with textboxes and labels to every “red box” instead of in this where was clicked button “ADD NEXT”. I suppose why it is happening. Because every “red box” refers to the same Session variable, but I don’t know how to fix it. I was trying during OnClick event passing unique ID and setting this ID as session variable name, but it wasn’t working as I expected.
Could you tell me, how to manage it? How looks the best way to recreate controls, how I can manage controls individually? If something is not clear, I will clarify. Always I was finding answers in stackoverflow, but this problem has outgrow me.
Best wishes.
(Sorry for my English, it doesn’t my native language)
My code.
Code for creating textboxes and some labels (Calculator.cs):
public string FLong
{
get
{
object o = ViewState["FLong"];
if (o == null)
return String.Empty;
return (string)o;
}
set { ViewState["FLong"] = value; }
}
public string FWide
{
get
{
object o = ViewState["FWide"];
if (o == null)
return String.Empty;
return (string)o;
}
set
{
ViewState["FWide"] = value;
}
}
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
CreateControlHierarchy();
ClearChildViewState();
}
protected virtual void CreateControlHierarchy()
{
Literal row = new Literal();
row.Text = "<div class='row surface'>";
Controls.Add(row);
//Add new TextBox;
Literal col = new Literal();
col.Text = "<div class='col-xs-4'>";
Controls.Add(col);
TextBox fLong = new TextBox();
fLong.ID = "fLong";
fLong.CssClass = "form-control";
//fLong.TextChanged += new EventHandler(Calculate_TextChanged);
//fLong.AutoPostBack = true;
fLong.Text = FLong;
Controls.Add(fLong);
Literal textLong = new Literal();
textLong.Text = "<span>ft. long x</span>";
Controls.Add(textLong);
RegularExpressionValidator flongValidate = new RegularExpressionValidator();
flongValidate.ControlToValidate = "fLong";
flongValidate.ErrorMessage = "Only Numbers allowed";
flongValidate.ValidationExpression = #"\d+";
flongValidate.ForeColor = System.Drawing.Color.Red;
flongValidate.Attributes["style"] = "display:block";
Controls.Add(flongValidate);
Literal colEnd = new Literal();
colEnd.Text = "</div>";
Controls.Add(colEnd);
//Add new Textbox
Literal col2 = new Literal();
col2.Text = "<div class='col-xs-4'>";
Controls.Add(col2);
TextBox fWide = new TextBox();
fWide.ID = "fWide";
fWide.CssClass = "form-control";
fWide.Text = FWide;
Controls.Add(fWide);
Literal textWide = new Literal();
textWide.Text = "<span>ft. wide</span>";
Controls.Add(textWide);
RegularExpressionValidator fwideValidate = new RegularExpressionValidator();
fwideValidate.ControlToValidate = "fWide";
fwideValidate.ErrorMessage = "Only Numbers allowed";
fwideValidate.ValidationExpression = #"\d+";
fwideValidate.ForeColor = System.Drawing.Color.Red;
fwideValidate.Attributes["style"] = "display:block";
Controls.Add(fwideValidate);
Literal col2End = new Literal();
col2End.Text = "</div>";
Controls.Add(col2End);
Literal rowEnd = new Literal();
rowEnd.Text = "</div>";
Controls.Add(rowEnd);
}
Code handling recreating (SurfaceCalculator.cs):
private int DefaultAmountControls = 1;
private string surfaceID;
public string SurfaceID
{
get { return surfaceID; }
set { surfaceID = value; }
}
public int Visibility
{
get
{
//store the object in session if not already stored
if (Session[surfaceID] == null)
Session[surfaceID] = DefaultAmountControls;
//return the object from session
return (int)Session[surfaceID];
}
set
{
if (value <= 5)
Session[surfaceID] = value;
else
Session[surfaceID] = 5;
}
}
protected void addSurface_Click(object sender, EventArgs e)
{
LinkButton b = (LinkButton)sender;
surfaceID = b.CommandArgument;
Visibility += 1;
}
protected override void OnInit(EventArgs e)
{
LinkButton addSurface = new LinkButton();
addSurface.Text = "+ Add surface";
addSurface.CommandArgument = surfaceID;
addSurface.Click += new EventHandler(addSurface_Click);
base.OnInit(e);
List<Calculator> c = Surface.Controls.OfType<Calculator>().ToList();
for (int i = 1; i <= Visibility; i++)
{
c.ElementAt(i - 1).Visible = true;
}
if (Visibility >= 5)
{
addSurface.Enabled = false;
}
Controls.Add(addSurface);
}
Code to adding many controls depending on SQL result
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
var listOfProjects = //GETTING FROM SQL
if(listOfProjects != null)
{
foreach (var proj in listOfProjects)
{
Panel placeHolder = new Panel();
placeHolder.CssClass = "surface";
placeHolder.ID = "placeHolder" + proj.DocumentID;
surfacesContainer.Controls.Add(placeHolder);
SurfaceCalculator newElement = (SurfaceCalculator)LoadControl("~/PATH_TO/CONTROL.ascx");
newElement.ID = "surfaceCalculator" + proj.DocumentID;
newElement.SurfaceID = newElement.ID;
placeHolder.Controls.Add(newElement);
}
}
}

how I save dynamically created Labels and Checkboxes values into sql server

how I save dynamically created Labels and Checkboxes values into sql server
protected void EventDuration_DDL_SelectedIndexChanged(object sender, EventArgs e)
{
int n = Int32.Parse(EventDuration_DDL.SelectedItem.ToString());
for (int i = 0; i < n; i++)
{
Label NewLabel = new Label();
NewLabel.ID = "Label" + i;
var eventDate = Calendar1.SelectedDate.Date.AddDays(i);
NewLabel.Text = eventDate.ToLongDateString();
CheckBox newcheck = new CheckBox();
newcheck.ID = "CheckBox" + i;
this.Labeldiv.Controls.Add(new LiteralControl("<span class='h1size'>"));
this.Labeldiv.Controls.Add(NewLabel);
this.Labeldiv.Controls.Add(new LiteralControl("</span>"));
this.Labeldiv.Controls.Add(new LiteralControl("<div class='make-switch pull-right' data-on='info'>"));
this.Labeldiv.Controls.Add(newcheck);
this.Labeldiv.Controls.Add(new LiteralControl("</div>"));
this.Labeldiv.Controls.Add(new LiteralControl("<br/>"));
}
}
protected void Wizard1_FinishButtonClick(object sender, WizardNavigationEventArgs e)
{
con.Open();
SqlCommand cmd1 = new SqlCommand("insert into Event(EventName,StartDate,EventDuration,StartTime,EndTime,SlotDuration) output inserted.EventId values(#EventName,#StartDate,#EventDuration,#StartTime,#EndTime,#SlotDuration)", con);
cmd1.Parameters.AddWithValue("#EventName", EventName_TB.Text);
cmd1.Parameters.AddWithValue("#StartDate", StartDate_TB.Text);
cmd1.Parameters.AddWithValue("#EventDuration", EventDuration_DDL.Text);
cmd1.Parameters.AddWithValue("#StartTime", StartTime_DDL.Text);
cmd1.Parameters.AddWithValue("#EndTime", EndTime_DDL.Text);
cmd1.Parameters.AddWithValue("#SlotDuration", SlotDuration_DDL.Text);
Int32 id = (Int32)cmd1.ExecuteScalar();
var label = Labeldiv.FindControl("Label1") as Label;
var checkbox = Labeldiv.FindControl("CheckBox1") as CheckBox;
using (SqlCommand cmd2 = new SqlCommand("insert into EventDays(EventDay,EventStatus)values(#EventDay,#EventStatus)", con))
{
int n = Int32.Parse(EventDuration_DDL.SelectedItem.ToString());
for (int i = 0; i < n; i++)
{
var paramDay = cmd2.Parameters.Add("#EventDay", SqlDbType.DateTime);
var paramStatus = cmd2.Parameters.Add("#EventStatus", SqlDbType.Int);
paramDay.Value = label.Text;
paramStatus.Value = checkbox.Checked ? 1 : 0;
cmd2.ExecuteNonQuery();
}
}
con.Close();
}
I have created Labels and CheckBoxes dynamically in EventDuration_DDL_SelectedIndexChanged.
now I want to save these values into sql server in Wizard1_FinishButtonClick.
how I save dynamically created Labels and Checkboxes values into sql server
.
.
.
.
..

You have to recreate those dynamically created labels and check boxes for the button click as well, because when the user clicks the finish button, that causes a post back to the server and the page is recreated, but the dynamic label and check box logic is not executed, thus your database saving logic cannot "find" these controls.
I recommend moving your dynamic label and check box creation logic to a separate method that can be called by the EventDuration_DDL_SelectedIndexChanged() and Wizard1_FinishButtonClick(), like this:
private void BuildDynamicControls()
{
int n = Int32.Parse(EventDuration_DDL.SelectedItem.ToString());
for (int i = 0; i < n; i++)
{
Label NewLabel = new Label();
NewLabel.ID = "Label" + i;
var eventDate = Calendar1.SelectedDate.Date.AddDays(i);
NewLabel.Text = eventDate.ToLongDateString();
CheckBox newcheck = new CheckBox();
newcheck.ID = "CheckBox" + i;
this.Labeldiv.Controls.Add(new LiteralControl("<span class='h1size'>"));
this.Labeldiv.Controls.Add(NewLabel);
this.Labeldiv.Controls.Add(new LiteralControl("</span>"));
this.Labeldiv.Controls.Add(new LiteralControl("<div class='make-switch pull-right' data-on='info'>"));
this.Labeldiv.Controls.Add(newcheck);
this.Labeldiv.Controls.Add(new LiteralControl("</div>"));
this.Labeldiv.Controls.Add(new LiteralControl("<br/>"));
}
}
Now in your event handlers, you can call this method, like this:
protected void EventDuration_DDL_SelectedIndexChanged(object sender, EventArgs e)
{
BuildDynamicControls();
}
protected void Wizard1_FinishButtonClick(object sender, WizardNavigationEventArgs e)
{
BuildDynamicControls();
}
Alternatively, you can call BuildDynamicControls() in the Page_Load. This takes care of other buttons on the page destroying the values when they cause a post back, like this:
protected void Page_Load(object sender, EventArgs e)
{
// Do other page load logic here
BuildDynamicControls();
}
Note: If you go this route, then you will not need to call BuildDynamicControls() in the EventDuration_DDL_SelectedIndexChanged() or Wizard1_FinishButtonClick() methods, because the Page_Load happens before either of those events in the page life-cycle.

Grab user input from dynamic text box

I have two buttons. One button that creates the Textbox and another that submits the information. I'm having trouble retrieving the users texts once the textbox has been created. Here is the code:
private void CreateTextBox(int j) //Creates the fields / cells
{
TextBox t = new TextBox();
t.ID = "Textbox" + j;
//t.Text = "Textbox" + j;
lstTextBox.Add(t);
var c = new TableCell();
c.Controls.Add(t);
r.Cells.Add(c);
table1.Rows.Add(r);
Session["test"] = lstTextBox;
}
protected void Button2_Click(object sender, EventArgs e)
{
string[] holder = new string[4];
for (int i = 0; i < holder.Length; i++)
{
holder[i] = "";
}
List<TextBox> lstTextBox = (Session["test"] as List<TextBox>);
if (lstTextBox.Count < Counter)
{
int i = lstTextBox.Count;
for (int j = 0; j < i; j++)
{
holder[j] = lstTextBox[j].Text;
}
SqlConnection conns = new SqlConnection(ConfigurationManager.ConnectionStrings["TestDBConnectionString1"].ConnectionString);
SqlCommand cmd = new SqlCommand("Insert into LoanerForm (field0, field1, field2, field3) Values (#field0, #field1, #field2, #field3)", conns);
cmd.CommandType = CommandType.Text;
cmd.Parameters.AddWithValue("#field0", holder[0]);
cmd.Parameters.AddWithValue("#field1", holder[1]);
cmd.Parameters.AddWithValue("#field2", holder[2]);
cmd.Parameters.AddWithValue("#field3", holder[3]);
conns.Open();
cmd.ExecuteNonQuery();
conns.Close();
}
Counter = 0;
Button1.Visible = true; //Going to submit data to SQL
}
Thank you in advance!

Here is how you create TextBoxes dynamically. It keeps track of the number of textboxes in ViewState.
<asp:Button runat="server" ID="Button1" OnClick="Button1_Click"
Text="Create TextBoxes" />
<asp:Button runat="server" ID="Button2" OnClick="Button2_Click"
Text="Save TextBoxes to Database" />
<asp:PlaceHolder runat="server" ID="PlaceHolder1"></asp:PlaceHolder>
public int Counter
{
get { return Convert.ToInt32(ViewState["Counter"] ?? "0"); }
set { ViewState["Counter"] = value; }
}
protected void Page_Load(object sender, EventArgs e)
{
// Need to reload those textboxes on page back
// Otherwise, they will becomes null
int total = Counter;
for (int i = 0; i < total; i++)
{
var textBox = new TextBox
{
ID = "TextBox" + i,
Text = "TextBox" + i
};
PlaceHolder1.Controls.Add(textBox);
}
}
private void CreateTextBox(int id)
{
var textBox = new TextBox
{
ID = "TextBox" + id,
Text = "TextBox" + id
};
PlaceHolder1.Controls.Add(textBox);
}
protected void Button1_Click(object sender, EventArgs e)
{
CreateTextBox(Counter);
Counter = Counter + 1;
}
protected void Button2_Click(object sender, EventArgs e)
{
int total = Counter;
for (int i = 0; i < total; i++)
{
var textbox = PlaceHolder1.FindControl("TextBox" + i) as TextBox;
var text = textbox.Text;
// Do something with text
}
}

Don't store the TextBoxes in Session; rather, create them on the page.
The trick is creating them at the right time EVERY time (i.e. with each PostBack). Try loading them OnLoad() for the page (or CreateChildControls() if possible).
Once you do that, ASP.NET will automatically associate the input with the TextBox and you should be able to reference them as you normally would or via .FindControl() of the parent.

I think You used big program for generating dynamic textboxes and inserting into data base.For retriving text from dynamically generated textboxes,use the code below..
Request.Form["Textbox" + i.ToString()]
where "i" represents the number of textboxes you generated.
For more info.Please Check the below link.
how to insert value to sql db from dynamically generated textboxes asp.net

Using Sessions in dynamic texboxes

Alright so I need to save each input from the textbox's in a session variable. The problem is that this is dynamic, meaning that the texbox ID is NatureTextbox_1, NatureTexbox_2 ect. And this makes it hard to save per session variable due to the infintite amount of texbox's available. I have been pounding my head against the wall trying to figure this out and am resorting to being a noob and asking you guys for your advice. If you can give me any information on what to do I'd appreciate it.
This is the C# Code (Remember the textbox's are dynamic meaning infinite):
protected void Page_Load(object sender, EventArgs e)
{
// Add any controls that have been previously added dynamically
for (int i = 0; i < TotalNumberAdded; ++i)
{
AddControls(i + 1);
}
}
private void AddControls(int controlNumber)
{
var newPanel = new Panel();
var natureLabel = new Label();
var dateLabel = new Label();
var fatalLabel = new Label();
var injurLabel = new Label();
var natureTextbox = new TextBox();
var dateTextbox = new TextBox();
var fatalTextbox = new TextBox();
var injurTextbox = new TextBox();
//Validations
var dateRegex = new RegularExpressionValidator();
//*****CURRENT IDEA THAT ISNT WORKING***********************************
Session["Nature" + (TotalNumberAdded - 1)] = natureTextbox.Text.ToString();
Session["Date" + (TotalNumberAdded - 1)] = dateTextbox.Text.ToString();
Session["Fatal" + (TotalNumberAdded - 1)] = fatalTextbox.Text.ToString();
Session["injury" + (controlNumber - 1)] = injurTextbox.Text.ToString();
//**********************************************************************
// textbox needs a unique id to maintain state information
natureTextbox.ID = "NatureTextBox_" + controlNumber;
dateTextbox.ID = "DateTextbox_" + controlNumber;
fatalTextbox.ID = "fatalTextbox_" + controlNumber;
injurTextbox.ID = "injurTextbox_" + controlNumber;
natureLabel.Text = "Nature Of Accident: ";
dateLabel.Text = "Date: ";
fatalLabel.Text = "Fatalities: ";
injurLabel.Text = "Injuries: ";
dateRegex.ID = "DateRegex_" + controlNumber;
dateRegex.Text = "Please enter in format MM/DD/YYY";
dateRegex.ValidationExpression = #"^(((0?[1-9]|1[012])/(0?[1-9]|1\d|2[0-8])|(0?[13456789]|1[012])/(29|30)|(0?[13578]|1[02])/31)/(19|[2-9]\d)\d{2}|0?2/29/((19|[2-9]\d)(0[48]|[2468][048]|[13579][26])|(([2468][048]|[3579][26])00)))$";
dateRegex.ControlToValidate = dateTextbox.ID;
// add the label and textbox to the panel, then add the panel to the form
newPanel.Controls.Add(new LiteralControl("<table><tr>"));
newPanel.Controls.Add(new LiteralControl("<br />"));
newPanel.Controls.Add(new LiteralControl("<td class='title-text' >"));
newPanel.Controls.Add(natureLabel);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text'width='180px'>"));
newPanel.Controls.Add(natureTextbox);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text' >"));
newPanel.Controls.Add(dateLabel);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text'>"));
newPanel.Controls.Add(dateTextbox);
newPanel.Controls.Add(new LiteralControl("<br />"));
newPanel.Controls.Add(dateRegex);
newPanel.Controls.Add(new LiteralControl("</td></tr>"));
newPanel.Controls.Add(new LiteralControl("<tr><td class='title-text'>"));
newPanel.Controls.Add(fatalLabel);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text'>"));
newPanel.Controls.Add(fatalTextbox);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text'>"));
newPanel.Controls.Add(injurLabel);
newPanel.Controls.Add(new LiteralControl("</td><td class='title-text'>"));
newPanel.Controls.Add(injurTextbox);
newPanel.Controls.Add(new LiteralControl("</td></tr></table><br /><hr />"));
AccidentPlaceHolder.Controls.Add(newPanel);
}
protected int TotalNumberAdded
{
get { return (int)(ViewState["TotalNumberAdded"] ?? 0); }
set { ViewState["TotalNumberAdded"] = value; }
}
protected void AccidentButton_Click(object sender, EventArgs e)
{
TotalNumberAdded++;
AddControls(TotalNumberAdded);
}
protected void PrevPage_Click(object sender, EventArgs e)
{
Response.Redirect("employment_driversapplication_personalinfo.aspx");
}
}

This works for me, bear in mind that the values are only persisted when you click 'add' - so i would suggest another save button or something to persist the values when not adding a new item.
public partial class TestRJF2 : System.Web.UI.Page
{
private IList<TextBox> AddedControls = new List<TextBox>();
protected override void CreateChildControls()
{
BuildControls();
base.CreateChildControls();
}
private void BuildControls()
{
for (var x = 0; x < TotalNumberAdded; x++)
{
var id = String.Format("NatureTextBox{0}", x);
//Check if control was already added
//only create controls that are new for this postback
if (AccidentPlaceHolder.FindControl(id) == null)
{
var textBox = new TextBox() {ID = id};
AccidentPlaceHolder.Controls.Add(textBox);
AddedControls.Add(textBox);
}
}
}
protected override void OnPreRender(EventArgs e)
{
foreach (var ctrl in AddedControls)
{
var key = ctrl.ID.Replace("TextBox", String.Empty);
Session[key] = ctrl.Text;
}
foreach (string session in Session.Keys)
{
System.Diagnostics.Debug.WriteLine(String.Format("{0} = {1}", session, Session[session]));
}
base.OnPreRender(e);
}
protected void AccidentButton_Click(object sender, EventArgs e)
{
TotalNumberAdded++;
BuildControls();
}
protected int TotalNumberAdded
{
get { return (int)(ViewState["TotalNumberAdded"] ?? 0); }
set { ViewState["TotalNumberAdded"] = value; }
}
}

NullReferenceException Controls.Add c# error

I'm getting the following error after I start debugging my program. Do you know how to fix this?
System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
It is referring to the line:
pnlDropDownList.Controls.Add(ddl);
inside the CreateDropDownLists method. Apparently the ddl must be a null object, even though I initialized ddl just before in this same method. Do you understand why I am receiving this error? See code below...
using System;
using System.Collections;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Diagnostics;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using ADONET_namespace;
using MatrixApp;
namespace AddFileToSQL
{
public partial class DataMatch : _Default
{
protected System.Web.UI.WebControls.PlaceHolder phTextBoxes;
protected System.Web.UI.WebControls.PlaceHolder phDropDownLists;
protected System.Web.UI.WebControls.Button btnAnotherRequest;
protected System.Web.UI.WebControls.Panel pnlCreateData;
protected System.Web.UI.WebControls.Literal lTextData;
protected System.Web.UI.WebControls.Panel pnlDisplayData;
Panel pnlDropDownList;
protected static string inputfile2;
static string[] headers = null;
static string[] data = null;
static string[] data2 = null;
static DataTable myInputFile = new DataTable("MyInputFile");
static string[] myUserSelections;
// a Property that manages a counter stored in ViewState
protected int NumberOfControls
{
get { return (int)ViewState["NumControls"]; }
set { ViewState["NumControls"] = value; }
}
public void EditRecord(object recordID)
{
SelectedRecordID = recordID;
// Load record from database and show in control
}
protected object SelectedRecordID
{
get
{
return ViewState["SelectedRecordID"];
}
set
{
ViewState["SelectedRecordID"] = value;
}
}
protected void OnPreLoad(object sender, EventArgs e)
{
//Create a Dynamic Panel
pnlDropDownList = new Panel();
pnlDropDownList.ID = "pnlDropDownList";
pnlDropDownList.BorderWidth = 1;
pnlDropDownList.Width = 300;
this.form1.Controls.Add(pnlDropDownList);
}
// Page Load
private void Page_Load(object sender, System.EventArgs e)
{
if (!Page.IsPostBack)
{
this.NumberOfControls = 0;
}
}
// Add DropDownList Control to Placeholder
private void CreateDropDownLists()
{
for (int counter = 0; counter < NumberOfControls; counter++)
{
DropDownList ddl = new DropDownList();
SqlDataReader dr = ADONET_methods.DisplayTableColumns(targettable);
ddl.ID = "DropDownListID" + (counter + 1).ToString();
ddl.DataTextField = "COLUMN_NAME";
ddl.DataValueField = "COLUMN_NAME";
ddl.DataSource = dr;
ddl.DataBind();
ddl.AutoPostBack = true;
ddl.EnableViewState = true; //Preserves View State info on Postbacks
ddl.Style["position"] = "absolute";
ddl.Style["top"] = 100 * counter + 80 + "px";
ddl.Style["left"] = 250 + "px";
ddl.SelectedIndexChanged += new EventHandler(this.OnSelectedIndexChanged);
pnlDropDownList.Controls.Add(ddl);
pnlDropDownList.Controls.Add(new LiteralControl("<br><br><br>"));
dr.Close();
}
}
private void CreateLabels()
{
for (int counter = 0; counter < NumberOfControls; counter++)
{
Label lbl = new Label();
lbl.ID = "Label" + counter.ToString();
lbl.Text = headers[counter];
lbl.Style["position"] = "absolute";
lbl.Style["top"] = 100 * counter + 50 + "px";
lbl.Style["left"] = 250 + "px";
pnlDropDownList.Controls.Add(lbl);
pnlDropDownList.Controls.Add(new LiteralControl("<br><br><br>"));
}
}
// Add TextBoxes Control to Placeholder
private void RecreateDropDownLists()
{
for (int counter = 0; counter < NumberOfControls; counter++)
{
DropDownList ddl = new DropDownList();
SqlDataReader dr = ADONET_methods.DisplayTableColumns(targettable);
ddl.ID = "DropDownListID" + (counter + 1).ToString();
ddl.DataTextField = "COLUMN_NAME";
ddl.DataValueField = "COLUMN_NAME";
ddl.DataSource = dr;
ddl.DataBind();
myUserSelections[counter] = "";
dr.Close();
ddl.AutoPostBack = true;
ddl.EnableViewState = false; //Preserves View State info on Postbacks
ddl.Style["position"] = "absolute";
ddl.Style["top"] = 100 * counter + 80 + "px";
ddl.Style["left"] = 250 + "px";
pnlDropDownList.Controls.Add(ddl);
pnlDropDownList.Controls.Add(new LiteralControl("<br><br><br>"));
}
}
// Create TextBoxes and DropDownList data here on postback.
protected override void CreateChildControls()
{
// create the child controls if the server control does not contains child controls
this.EnsureChildControls();
// Creates a new ControlCollection.
this.CreateControlCollection();
// Here we are recreating controls to persist the ViewState on every post back
if (Page.IsPostBack)
{
RecreateDropDownLists();
RecreateLabels();
}
// Create these conrols when asp.net page is created
else
{
PopulateFileInputTable();
CreateDropDownLists();
CreateLabels();
}
// Prevent child controls from being created again.
this.ChildControlsCreated = true;
}
private void AppendRecords()
{
switch (targettable)
{
case "ContactType":
for (int r = 0; r < myInputFile.Rows.Count; r++)
{ ADONET_methods.AppendDataCT(myInputFile.Rows[r]); }
break;
case "Contact":
for (int r = 0; r < myInputFile.Rows.Count; r++)
{ ADONET_methods.AppendDataC(myInputFile.Rows[r]); }
break;
case "AddressType":
for (int r = 0; r < myInputFile.Rows.Count; r++)
{ ADONET_methods.AppendDataAT(myInputFile.Rows[r]); }
break;
default: throw new ArgumentOutOfRangeException("targettable type", targettable);
}
}
// Read all the data from TextBoxes and DropDownLists
protected void btnSubmit_Click(object sender, System.EventArgs e)
{
int cnt = FindOccurence("DropDownListID");
EditRecord("DropDownListID" + Convert.ToString(cnt + 1));
AppendRecords();
pnlDisplayData.Visible = false;
}
private int FindOccurence(string substr)
{
string reqstr = Request.Form.ToString();
return ((reqstr.Length - reqstr.Replace(substr, "").Length) / substr.Length);
}
#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
{
InitializeComponent();
base.OnInit(e);
}
private void InitializeComponent()
{
(this.btnSubmit_Click);
}
#endregion
}
}

I think it's referring to "pnlDropDownList" being a Null object. That function must be getting called before "pnlDropDownList = new Panel();" in "OnPreLoad". Use breakpoints to step through the source and follow the code-path. I'm sure you'll find this is the case.

You might want to try creating your dynamic controls in PreInit, I have a hunch that the Panel has not yet been initialized and hence the exception
Check out the Page Lifecycle