title: ItemsControl item, going out of view
body: <p>I have a <code>ScrollViewer</code> within which, I have an <code>ItemsControl</code>. The <code>ItemsControl</code> is bound to an <code>ObservableCollection</code>. The <code>ItemsControl</code> has an <code>ItemTemplate</code>, where in I provide a <code>TextBox</code> to display the data.</p>
  <p>The data is getting displayed correctly. I have added a popup to each of the <code>TextBox</code> to display additional data with the placement target being Top.</p>
  <p>The problem I am facing is when I scroll if an item goes out of view, I need to hide the popup and display it again when the item appears.</p>
  <p>I have subscribed to the scrollviewer's <code>ScrollChanged</code> event, but how do I get hold of the item / <code>TextBox</code> which is going out of scope to hide the popup?</p>