CancellationToken

.cs

public class MainViewModel : BaseViewModel
    {
        private CancellationTokenSource cancellation;

        #region mvvm
        private string _text;
        public string Text
        {
            get => _text;
            set
            {
                _text = value;
                OnPropertyChanged();
            }
        }
        public Command Start { get; set; }
        public Command Stop { get; set; }
        public MainViewModel()
        {
            Start = new Command(StartExecute);
            Stop = new Command(StopExecute);
        }
        #endregion

        private void StopExecute(object obj)
        {
            cancellation?.Cancel();
        }

        private void StartExecute(object obj)
        {
            MainMethod();
        }

        public async void MainMethod()
        {
            cancellation = new CancellationTokenSource();

            await SetDataGrid(cancellation.Token);

            UpdateMethod();
            SerialPortDialog();
        }

        public Task SetDataGrid(CancellationToken ct)
        {
            Task task = null; 
            task = Task.Run(() =>
            {
                try
                {
                    for (int i = 0; ; i++)
                    {
                        //Проверяем, была ли вызвана отмена потока, если да,
                        //то генерируем исключение отмены потока
                        if (ct.IsCancellationRequested)
                            throw new TaskCanceledException(task);

                        Thread.Sleep(150);

                        Text = i.ToString();
                    }
                }
                catch (TaskCanceledException)
                {
                    MessageBox.Show("Задача была отменена");
                }
            });

            return task;
        }

        public void UpdateMethod()
        {
            MessageBox.Show(MethodBase.GetCurrentMethod().ToString());
        }

        public void SerialPortDialog()
        {
            MessageBox.Show(MethodBase.GetCurrentMethod().ToString());
        }
    }