public MainWindow()
        {
            InitializeComponent();

            dbo = new TaskNodeContext();

            dbo.TaskNodes.Load();

            taskGrid.ItemsSource = dbo.TaskNodes.Local.ToBindingList();
        }
        //Обработка события нажатия CheckBox состояния выполнена
        private void IsFinish_Click(object sender, RoutedEventArgs e)
        {
            if ((taskGrid.SelectedItem as TaskNode) != null)
            {
                var node = taskGrid.SelectedItem as TaskNode;

                if (node.Title == null)
                {
                    ShowInstuction();
                    if ((e.OriginalSource as CheckBox).IsChecked == true)
                    {
                        (e.OriginalSource as CheckBox).IsChecked = false;
                    }
                }

                else
                { //Если TaskNode !=null
                    (taskGrid.SelectedItem as TaskNode).IsStart    = false;
                    (taskGrid.SelectedItem as TaskNode).IsFinish   = true;
                    (taskGrid.SelectedItem as TaskNode).IsProgress = false;

                    DateTime now = DateTime.Now;
                    (taskGrid.SelectedItem as TaskNode).DateFinish = now.Date;


                    dbo.SaveChanges();

                    dbo = new TaskNodeContext();

                    dbo.TaskNodes.Load();

                    taskGrid.ItemsSource = dbo.TaskNodes.Local.ToBindingList();
                }
            }
            else
            {
                ShowInstuction();
                (e.OriginalSource as CheckBox).IsChecked = false;
            }
        }