Использование анонимных делегатов с.NET ThreadPool. QueueUserWorkItem

Вы должны добавить свой динамический элемент управления в коллекцию элементов управления

int controlCounts = 0;

private void addControls_Click(object sender, EventArgs e)
{

    controlCounts++;

    TextBox txt_QTY = new TextBox();
    txt_QTY.Location = new Point(100 * controlCounts, 100);
    txt_QTY.Name = "txt_QTY" + controlCounts;
    Controls.Add(txt_QTY);
    txt_QTY.TextChanged += txt_QTY_TextChanged;

    TextBox txt_Price = new TextBox();
    txt_Price.Location = new Point(100 * controlCounts, 200);
    txt_Price.Name = "txt_Price" + controlCounts;
    Controls.Add(txt_Price);
    txt_Price.TextChanged += txt_Price_TextChanged;

    TextBox txt_Total = new TextBox();
    txt_Total.Location = new Point(100 * controlCounts, 300);
    txt_Total.Name = "txt_Total" + controlCounts;
    Controls.Add(txt_Total);
}

private void txt_QTY_TextChanged(object sender, EventArgs e)
{
    TextBox txt_QTY = (TextBox)sender;
    string index = txt_QTY.Name.Substring("txt_QTY".Length);
    updateTotal(index);
}

private void txt_Price_TextChanged(object sender, EventArgs e)
{
    TextBox txt_Price = (TextBox)sender;
    string index = txt_Price.Name.Substring("txt_Price".Length);
    updateTotal(index);
}

private void updateTotal(string index)
{
    TextBox txt_QTY = (TextBox)Controls["txt_QTY" + index];
    TextBox txt_Price = (TextBox)Controls["txt_Price" + index];
    TextBox txt_Total = (TextBox)Controls["txt_Total" + index];

    if ((txt_QTY.Text != "") && (txt_Price.Text != ""))
    {
        txt_Total.Text = (Convert.ToInt32(txt_QTY.Text) * Convert.ToInt32(txt_Price.Text)).ToString();
    }

}