private void AddTask_OnClick(object sender, RoutedEventArgs e)
        {
            CreateUpdateTaskDialog addTaskDialog = new CreateUpdateTaskDialog();

            if (addTaskDialog.ShowDialog() == true)
            {
                _todoTasks.Add(new TodoTask(addTaskDialog.NewTaskDescription, addTaskDialog.NewTaskDeadline, addTaskDialog.NewTaskDeadlineTime));
                SaveCollectionsToJson();
                TodoTaskListChanged();
            }
        }
        private void EditTaskCommand_Executed(object sender, ExecutedRoutedEventArgs e)
        {
            var item = TodoTask_ListView.SelectedItem as TodoTask;
            CreateUpdateTaskDialog updateTaskDialog = new CreateUpdateTaskDialog(item);

            if (updateTaskDialog.ShowDialog() == true)
            {
                _todoTasks.Single(t => t.Equals(item)).UpdateTodoTask(
                    updateTaskDialog.NewTaskDescription, updateTaskDialog.NewTaskDeadline, updateTaskDialog.NewTaskDeadlineTime, item.ProgressValue);
                SaveCollectionsToJson();
                TodoTaskListChanged();
            }
        }