title: collection changed event using reactive extensions
body: <p>I am trying to subscribe a collection to ViewModel using reactive extension</p>
  
  <pre><code>AllTags = tagList.ToObservable(Scheduler.ThreadPool);
  </code></pre>
  
  <p>and this is subscription</p>
  
  <pre><code>subscription = Model.GetAllEntities().Subscribe(x =&gt; RefreshAllEntities(x));
  </code></pre>
  
  <p>My question is that if something is added to tagList and call OnNext gives notification. But when i delete a item from collection how can be keep in sync. There is no notification. Kindly help.</p>