Forms Data Controls :: Load Dynamic Control When Button Was Fired?

how to call LoadDynamicControl() when btnPopUp was click?

protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
//..........
}

LoadDynamicControl(); // if i don't call this function here,i cannot find control to update,but if i call it here. It's will fire with any event.

}
protected void btnPopUP_Click(object sender, EventArgs e)
{
ModalPopupExtender1.Show();
}
protected void btnUpdate_Click(object sender, EventArgs e)
{
updateproductParameter();
ModalPopupExtender1.Show();
}