title: NotifyCollectionChangedEventHandler - how to clear collection
body: <p>I am working with this sample: <a href="http://www.arcgis.com/home/item.html?id=ef6a80c07fb84f84a5fe5192221f582c" rel="nofollow">http://www.arcgis.com/home/item.html?id=ef6a80c07fb84f84a5fe5192221f582c</a>
  specifically with “GraphicsDataSourcesDemo”, which uses Silverlight API.
  It allow for loading csv file with Lat Long coordinates, which are displayed as points on the map. In my own application I successfully implemented part about displaying points, but I have problem with a Clear button (which is not implemented in the included sample code). Since <code>INotifyCollectionChanged</code> and <code>StreamReader</code> are used, standard method like:</p>
  
  <pre><code>private void GPSClearButton_Click(object sender, RoutedEventArgs e)
  {
    GraphicsLayer graphicsLayer = Map.Layers["data"] as GraphicsLayer;
    graphicsLayer.ClearGraphics();            
  }
  </code></pre>
  
  <p>does not work.</p>
  
  <p>I would appreciate any advice on how to make displayed points disappear from my map (after user decide so by clicking a button Clear).</p>