ASP.NET Several controls were found with the same identifier 'x'. FindControl

Question

Getting the following error

Several controls were found with the same identifier 'ltlItemCode'. FindControl requires that controls have unique identifiers.

This error does not occur when the page loads, but when I change the value of the drop-down list that has AutoPostBack = "true".

Code

    //Number of Services
    numberofServices = Int32.Parse(DCCFunctions.GetNumServicesPerRoom(roomId.ToString()));
    additionalServices = new UserControls_AdditionalService[numberofServices - 1];

    String htmlTable = String.Empty;
    Int32 cell = 1;
    Int32 rows = numberofServices;
    Int32 cols = 4;


    TableHeaderRow h = new TableHeaderRow();
    TableHeaderCell hc1 = new TableHeaderCell();
    hc1.Text = "Item Description";
    h.Cells.Add(hc1);
    TableHeaderCell hc2 = new TableHeaderCell();
    hc2.Text = "Item Price";
    h.Cells.Add(hc2);
    TableHeaderCell hc3 = new TableHeaderCell();
    hc3.Text = "Item Quantity";
    h.Cells.Add(hc3);
    TableHeaderCell hc4 = new TableHeaderCell();
    hc4.Text = "Item Sub Total";
    h.Cells.Add(hc4);
    Table1.Rows.Add(h);

    // Open database connection
    DBConnection conn = new DBConnection();

    // Retrieve details
    SqlCommand sqlGetDetails = conn.SetStoredProcedure("spGetAdditionalServicesDetails");
    DBConnection.AddNewParameter(sqlGetDetails, "@roomId", ParameterDirection.Input, SqlDbType.Int, roomId);

    try
    {
        conn.Open();

        SqlDataReader reader_list = sqlGetDetails.ExecuteReader();
        if (reader_list.HasRows)
        {
            while (reader_list.Read())
            {
                //returnVal = reader_list["Num"].ToString();
                htmlTable += "<tr>" + Environment.NewLine;
                TableRow r = new TableRow();

                additionalServices[cell - 1] = (ASP.usercontrols_additionalservice_ascx)LoadControl("~/UserControls/AdditionalService.ascx");

                Literal ItemCode = (Literal)additionalServices[cell - 1].FindControl("ltlItemCode") as Literal;
                ItemCode.Text = reader_list["itemDescription"].ToString();


                Literal ItemPrice = (Literal)additionalServices[cell - 1].FindControl("ltlItemPrice") as Literal;
                ItemPrice.Text = "€" + reader_list["unitPrice"].ToString();

                Literal ItemTotal = (Literal)additionalServices[cell - 1].FindControl("ltlTotalPrice") as Literal;
                ItemTotal.Text = "€" + "0";

                TableCell ItemCodeCell = new TableCell();
                ItemCodeCell.Controls.Add((Literal)additionalServices[cell - 1].FindControl("ltlItemCode") as Literal);

                TableCell ItemCodePriceCell = new TableCell();
                ItemCodePriceCell.Controls.Add((Literal)additionalServices[cell - 1].FindControl("ltlItemPrice") as Literal);

                TableCell ItemCodeTotalCell = new TableCell();
                ItemCodeTotalCell.Controls.Add((Literal)additionalServices[cell - 1].FindControl("ltlTotalPrice") as Literal);

                TableCell c = new TableCell();
                DropDownList qtyList = (DropDownList)additionalServices[cell - 1].FindControl("qtyList") as DropDownList;
                qtyList.Items.Add(new System.Web.UI.WebControls.ListItem("Select Quantity...", "0"));
                qtyList.DataBind();

                for (Int32 count = 1; count < 101; count++)
                {
                    qtyList.Items.Add(new System.Web.UI.WebControls.ListItem(count.ToString(),count.ToString()));
                }
                //c.ColumnSpan = 5;
                c.Controls.Add((DropDownList)additionalServices[cell - 1].FindControl("qtyList") as DropDownList);


                r.Cells.Add(ItemCodeCell);
                r.Cells.Add(ItemCodePriceCell);
                r.Cells.Add(c);
                r.Cells.Add(ItemCodeTotalCell);
                //r.Controls.Add(additionalServices[cell - 1]);
                //cell += 1;

                // Add the row
                Table1.Rows.Add(r);
            }
        }
        reader_list.Close();
    }
    catch (Exception ex)
    {
        M1Utils.ErrorHandler(ex);
    }
    finally
    {
        conn.Close();
    }`

Answer 1

ItemCodeCell.Controls.Add((Literal)additionalServices[cell - 1].FindControl("ltlItemCode") as Literal);

I assume this is a problem, it looks like you are adding the same control over and over, but I'm not sure. Try changing the .ID of this newly added Literal.

, "EnsureID()" , , . -

Literal duplicateLiteral = (Literal)additionalServices[cell - 1].FindControl("ltlItemCode") as Literal;
duplicateLiteral.EnsureID();
ItemCodeCell.Controls.Add(duplicateLiteral);

, , , duplicateLiteral, .

Answer 2

, , , . , Controls . , :

TableHeaderRow h = new TableHeaderRow();    
TableHeaderCell hc1 = new TableHeaderCell();    
hc1.Text = "Item Description";    
h.Cells.Add(hc1);    
TableHeaderCell hc2 = new TableHeaderCell();    
hc2.Text = "Item Price";    
h.Cells.Add(hc2);    
TableHeaderCell hc3 = new TableHeaderCell();    
hc3.Text = "Item Quantity";    
h.Cells.Add(hc3);    
TableHeaderCell hc4 = new TableHeaderCell();    
hc4.Text = "Item Sub Total";    
h.Cells.Add(hc4);    
Table1.Rows.Add(h);

:

TableHeaderRow h = new TableHeaderRow();   
Table1.Rows.Add(h); 
TableHeaderCell hc1 = new TableHeaderCell();
h.Cells.Add(hc1);   
hc1.Text = "Item Description";      
TableHeaderCell hc2 = new TableHeaderCell();
h.Cells.Add(hc2);    
hc2.Text = "Item Price";       
TableHeaderCell hc3 = new TableHeaderCell();
h.Cells.Add(hc3);    
hc3.Text = "Item Quantity";      
TableHeaderCell hc4 = new TableHeaderCell();
h.Cells.Add(hc4);    
hc4.Text = "Item Sub Total";    

, Controls, , UniqueID. X X.Controls X Controls, .

Answer 3

, EnsureID , , .

, . , . FindControl , ...? , , . , , - ? - :

Literal ItemCode = (Literal)additionalServices[cell - 1].FindControl("ltlItemCode") as Literal;
ItemCode.Text = reader_list["itemDescription"].ToString();

Literal ItemCode2 = new Literal();  //create a new control
ItemCode2.Text = ItemCode.Text;     //copy the data you need

TableCell ItemCodeCell = new TableCell();
ItemCodeCell.Controls.Add(ItemCode2);  // add new control