dynamic textbox creation on buttn and getting its value back

on btnGetSubjects_Clik Event The Following Code Runs

Retrieve GSubj = new Retrieve();

DataSet DS = new DataSet();

DS = GSubj.GetSubjects(SclID, ClassID);

if (DS != null)

{

if (DS.Tables[0].Rows.Count > 0)

{

Table CreatTable = new Table();

CreatTable.ID = "tblDynamic";

//DS.Tables[0].Rows[rowNum][columnName].ToString();

for (int i = 0; i < DS.Tables[0].Rows.Count; i++)

{

TableRow row;

row = new TableRow();

row.Width = 250;

TableCell cell1 = new TableCell();

cell1.Width = 130;

Lbl = new Label();

Lbl.ID = DS.Tables[0].Rows[i][0].ToString();

Lbl.Text = DS.Tables[0].Rows[i][1].ToString();

cell1.Controls.Add(Lbl); // Creating Labels With Subject ID as Label ID and Subject Name as Label Text

row.Cells.Add(cell1);

TableCell cell2 = new TableCell();

txtbox = new TextBox();

txtbox.ID = "Sub" + DS.Tables[0].Rows[i][0].ToString();

txtbox.Attributes.Add("runat", "Server");

cell2.Controls.Add(txtbox); // Creating Textbox With Subject ID as Textbox ID

row.Cells.Add(cell2);

CreatTable.Rows.Add(row);

}

TablePlaceHolder.Controls.Add(CreatTable);

}

After Creating I am Trying to get the filled values

protected void btnSubmit_Click(object sender, EventArgs e)

{

Hashtable Subjects = new Hashtable();

foreach (Control ctrl in TablePlaceHolder.Controls)

{

if (ctrl is TextBox)

{

Subjects.Add(((TextBox)ctrl).ID, ((TextBox)ctrl).Text); // Filling Subject Code and marks to the Hash Table

}

but the place holder is null and its not showing any values

Code in aspx Page

please suggest me

Advance Thank you...