title: Count New Items in WPF Listbox
body: <p>I have a <code>listbox</code> and it's source is Binded to a <code>XmlDataProvider</code>. and a RSS link for the source of <code>XmlDataProvider</code>. It's all working correctly, getting feeds and displaying them in the <code>listbox</code>. I have a <code>DispatcherTimer</code> in the code that Refresh the <code>XmlDataProvider</code> source every 10 minutes. Now All I need is to count the new items added in the <code>ListBox</code> in each Refresh Interval.</p>
  
  <p>Can anyone help me to implement a way to count only new items added in the listbox in each Refresh Time Interval? Please Help.</p>