private void AddPerson_Click(object sender, RoutedEventArgs e)
        {
            if (null == _cache)
            {
                _cache = new MultiLevelCache <Person>();
            }

            var person = new Person {
                Name = NameTextBox.Text, Age = AgeTextBox.Text
            };

            if (!_cache.ContainsKey(person.Name))
            {
                _cache.Add(person.Name, person);
            }
            else
            {
                MessageBox.Show("Cannot add a person with the same name!");
            }
            People.ItemsSource = _cache.Values;
        }
 private void ReadFromStorage_Click(object sender, RoutedEventArgs e)
 {
     _cache             = new MultiLevelCache <Person>();
     People.ItemsSource = _cache.Values;
 }