Web Forms :: Lost Child Control After Postback In Panel Control

I had a little project is create dynamic control. My project had get detail of content and replace in sign string, Add control in sign. After click button I will find in control, I had added on page load in panel. I can't get value in child control panel, Don't have control in panel. My source is

protected void Page_Load(object sender, EventArgs e)
{
string config_design = GetConfigueKey(configDesign);
Genform(config_design, GetContent(config_design));
if (IsPostBack)
{
btn_submit_click(sender, e);
}
else
{
string config_design = GetConfigueKey(configDesign);
Genform(config_design, GetContent(config_design));
}
}
protected String GetContent(string designname)
{
string rev = "";
mClsDB = new clsConn();
strSql = "SELECT STR_DESIGN_CONTENT,STR_DESIGN_NAME,INT_FORM_ID FROM TBL_DESIGN WHERE INT_DESIGN_ID = " + designname + " ";
DataTable dt = mClsDB.GetDataTable(strSql);
if (dt != null)
{
if (dt.Rows.Count > 0)
{
rev = dt.Rows[0]["STR_DESIGN_CONTENT"].ToString();
}
}
return rev;
}
protected void Genform(string designname, string content)
{
string rev = content;
mClsDB = new clsConn();
//strSQL = " SELECT INT_FIELD_ID,STR_FIELD_NAME,STR_FIELD_SIZE,STR_FIELD_CSS,STR_FIELD_DEFAULTVALUE,BIT_FIELD_VISIBLE,INT_FIELD_VALIDATE_TYPE,STR_FIELD_MINMAX,STR_FIELD_TYPE_NAME ";..................