Three Dropdownlist Dynamic Controls ViewState Issue

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.NET3.5

.NET

C#3.5

I am using Asp.net C#
I am creating Three Dropdownlist Dynamic Controls on page_Preinit
On generating the controls on page_Preinit I bind the datasource for the fist time

on First dropdownlist SelectedIndexChanged Event I Change the Datasource of the Second DropDowns
And on Second dropdownlist SelectedIndexChanged Event I change the datasource of the thrid downpdown

But Problem is Second dropdownlist loses the SelectedValue

public void GenerateTheDynamicControls()
        {
            if (dtMainData != null)
            {
                Table tblData = new Table();
                tblData.Caption = "Drop Down";
                tblData.Width = Unit.Percentage(100);
                tblData.CellSpacing = 2;
                tblData.CellPadding = 4;
                tblData.BorderStyle = BorderStyle.Solid;
                foreach (DataRow dr in dtMainData.Rows)
                {
                    TableRow tr = new TableRow();
                    tr.BorderStyle = BorderStyle.Solid;
                    if (dr["ControlType"].ToString() == "DropDownList")
                    {
                        DropDownList ddl = new DropDownList();
                        TableCell cH = new TableCell();
                        System.Web.UI.WebControls.Label lbl = new System.Web.UI.WebControls.Label();
                        lbl.Text = "" + dr["ControlLabelName"].ToString() + " : ";
                        cH.Controls.Add(lbl);
                        tr.Cells.Add(cH);
                        TableCell cH2 = new TableCell();
                        
                       
                        ddl.ClientIDMode = System.Web.UI.ClientIDMode.Static;
                        ddl.ID = "" + dr["ControlName"].ToString();
                        List<string> lstDdlDataSource = new List<string>();
                        foreach (var ns in dr["ControlDataSourceString"].ToString().Split(';'))
                        {
                            if (ns.Trim() != "")
                            {
                                lstDdlDataSource.Add(ns);
                            }
                        }
                        ddl.DataSource = lstDdlDataSource;
                        ddl.DataBind();
                        ddl.Items.Insert(0, "Select");
                        if (dr["ConnectedToControl"].ToString().ToLower() == "true")
                        {
                            ddl.AutoPostBack = true;
                            ddl.SelectedIndexChanged += new EventHandler(dropDowns_SelectedIndexChanged);                            
                        }
                        ScriptManager.GetCurrent(this).RegisterAsyncPostBackControl(ddl);
                        cH2.Controls.Add(ddl);
                        tr.Cells.Add(cH2);
                    }
                    tblData.Rows.Add(tr);
                }
                phCreateControls.Controls.Add(tblData);
                UpdatePanel1.Update();
            }
        }

void dropDowns_SelectedIndexChanged(object sender, EventArgs e)
        {                        
            //bc.showJavascriptMessagesForScriptManagerPages("It Works", this.Page);
            if (dtMainData != null)
            {
                DataRow[] drSelection = dtMainData.Select("ControlName='" + (sender as DropDownList).ID.ToString()+ "'"); ;
                if (drSelection != null && drSelection.Length >= 1)
                {
                    DropDownList ConnectedToControlName = phCreateControls.FindControl("" + drSelection[0]["ConnectedToControlName"]) as DropDownList;
                    string[] ConnectedToControlDataSourceValues = drSelection[0]["ConnectedToControlDataSourceValues"].ToString().Split(',');
                    List<string> lstDdlDataSource = new List<string>();
                    foreach (string str in ConnectedToControlDataSourceValues)
                    {
                        if (str.Contains((sender as DropDownList).SelectedValue.ToString()))
                        {
                            string [] valuesForData = str.Replace("[","").Replace("]","").Split('»');
                            foreach (var ns in valuesForData[1].Split(';'))
                            {
                                if (ns.Trim() != "")
                                {
                                    lstDdlDataSource.Add(ns);
                                }
                            }
                        }
                    }
                    ConnectedToControlName.DataSource = lstDdlDataSource;
                    ConnectedToControlName.DataBind();
                }
            }
            UpdatePanel1.Update();
        }