public void AddItem(CheckActivity newItm)
 {
     if (newItm != null)
     {
         Items.Add(newItm);
     }
 }
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            Button thisButton = (Button)sender;

            if (null == thisButton)
            {
                return;
            }

            CheckActivity thsActivity = (CheckActivity)thisButton.DataContext;

            if (null == thsActivity)
            {
                return;
            }
            thsActivity.IsChecked = !thsActivity.IsChecked;

            if (thsActivity.IsChecked)
            {
                thsActivity.Name = "[✓]" + thsActivity.Name.Substring(3);
            }
            else
            {
                thsActivity.Name = "[ ]" + thsActivity.Name.Substring(3);
            }

            UpdateItems();
        }
        private void Delete_MenuItem_Click(object sender, RoutedEventArgs e)
        {
            Button MyButton = null;

            if (sender is MenuItem mnu)
            {
                ContextMenu MyContextMenu = (ContextMenu)mnu.Parent;
                MyButton = MyContextMenu.PlacementTarget as Button;
            }
            if (null == MyButton)
            {
                return;
            }

            CheckActivity thsActivity = (CheckActivity)MyButton.DataContext;

            if (null == thsActivity)
            {
                return;
            }

            Items.Remove(thsActivity);
        }