DataGridView bound to a Dictionary and updated with a thread

Answer 1

You have to use a lock statement to protect your shared resource : the dictionary.

private object _lock = new object();

private void Reset()
{
    lock(_lock)
    {
        // your code here
    }
}

void f_PriceChanged(Objet f, eventData e)
{
    lock(_lock)
    {
        if (prices.ContainsKey(e.ItemText))
            prices[e.ItemText] = e.price;
        else
            prices.Add(e.ItemText, e.price);
    }

}

You'll have to make f_PriceChanged() a member.