asp.net retain list values between postbacks

Hello everybody and thanks in advance,

I've made a class in my .cs file and then declared a list<> of it like this...

    public partial class MyClass : System.Web.UI.Page
    {
        public List<PrecioStock> PreciosYStocks = new List<PrecioStock>();


        protected void Page_Load(object sender, EventArgs e)
        {
...
...

    public class PrecioStock
    {
        public string Precio;
        public string Stock;

        public PrecioStock(string Precio, string Stock)
        {
            this.Precio = Precio;
            this.Stock = Stock;
        }

        public void SetPrecio(string nuevoPrecio)
        {
            this.Precio = nuevoPrecio;
        }

        public void SetStock(string nuevoStock)
        {
            this.Stock = nuevoStock;
        }

        public string GetPrecio()
        {
            retu this.Precio;
        }

        public string GetStock()
        {
            retu this.Stock;
        }

    }

Then, I fill it this way, with some textboxes' texts...

            PreciosYStocks.Clear();

            foreach (ListItem items in ControlListaGenerico.Items)
            {
                if (items.Selected)
                {
                    for (int i = 0; i < TablaDeDatos.Rows.Count; i++)
                    {
                        if(items.Value.Equals(TablaDeDatos.Rows[i]["ID_FORMATO"].ToString()))
                        {
                            TextBox Precio = (TextBox)Precio_Stock_PN.FindControl("NuevoPrecioTB_" + items.Value);
                            Precio.Text = TablaDeDatos.Rows[i]["PRECIO"].ToString();

                            TextBox Stock = (TextBox)Precio_Stock_PN.FindControl("NuevoStockTB_" + items.Value);
                            Stock.Text = TablaDeDatos.Rows[i]["STOCK"].ToString();

                            PreciosYStocks.Add(new PrecioStock(Precio.Text, Stock.Text));

                            break;
                        }
                    }
                }
            }

Well, it seems to fill well, but the problem is that when I click the UPDATE button of the DetailsView, this generates a postback event, the data is lost and I'm not be able to access to it anymore.

So, how can I access to it after postback? I mean, make it persistent.

I've read about "viewState" and "Session" ways but don't know how to implement them, in case they are the answer to this.

Please, help and thanks again.