public static event Action Changed;

   private static void test()
        {
            for (int i = 0; i < 10; i++)
            {
                Changed(i);
            }
        }
   public static void Upload()//SqlConnection connection)
        {

            //if(connection.State != ConnectionState.Open)
            //    connection.Open();

            Thread thr;
            thr = new Thread(test);
            thr.Start();

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            FileCarrier.Changed += OnProgressChange;
            //FileCarrier.ReportDDProgress += OnProgressChange;
            FileCarrier.Upload();
            
        }

        private void OnProgressChange(int a)
        {
            MessageBox.Show(a.ToString());
        }
    }