title: Custom ItemsSource property for a UserControl
body: <p>Does anyone know how to make a custom <code>ItemsSource</code>?</p>
  
  <p>What I want to do is to make an <code>itemsSource</code> to my own <code>UserControl</code> so that it could be bound by <code>ObservableCollection&lt;&gt;</code>.</p>
  
  <p>Also, I could know Whenever the number of items in the <code>itemsSource</code> updated, so as to do further procedures.</p>
  
  <p>Thank you so much.</p>