private void startBut_Click(object sender, EventArgs e) { int colSize = int.Parse(numSizeText.Text); countText.Clear(); InitVals(vals, colSize); var task = Task.Run(() => { int size = PrimeUtils.CountPrimes(vals, colSize); return(size); }); task.ContinueWith((ant) => { int res = ant.Result; this.countText.Text = res.ToString(); startBut.Enabled = true; }, TaskScheduler.FromCurrentSynchronizationContext()); startBut.Enabled = false; }