private async void Button_Click(object sender, RoutedEventArgs e)
        {
            Random rnd = new Random();

            int range = -1;
            int from = -1;
            int to = -1;         
            var progress = new Progress<int>(value => progressBar.Value = value);
            
            if (Int32.TryParse(TextBoxFrom.Text, out from) && Int32.TryParse(TextBoxTo.Text, out to) && Int32.TryParse(TextBoxRange.Text, out range))
            {
                progressBar.Minimum = 0;
                progressBar.Maximum = range;

                await Task.Run(() =>
                {
                    string num = String.Empty;
                    for (int i = 1; i <= range; i++)
                    {
                        String rand = rnd.Next(from, to).ToString();
                        randNum.Add(rand);
                        Dispatcher.BeginInvoke((Action)(() => TextBoxNumbers.AppendText(rnd.Next(from, to).ToString())));
                        Dispatcher.BeginInvoke((Action)(() => TextBoxNumbers.AppendText(Environment.NewLine)));
                        ((IProgress < int>)progress).Report(i);
                        System.Threading.Thread.Sleep(1000);
                    }
                }); 
            }
            else
            {
                MessageBox.Show("Wszystkie wartosci muszą być liczbami calkowitymi!");
            }
            
        }