title: Check if object has PropertyChanged Event attached to it
body: <p>When my window is loaded, I have an ObservableCollection that is populated and a PropertyChanged event is added to each item. However, after the initial loading items can be added to the ObservableCollection. I want to be able to listen for collection changes on the ObservableCollection, check if an item was added and then attach an event listener to it if it was added.</p>
  
  <p>To do this, I'd like to be able to check if the PropertyChanged property is defined for each individual item and attach a PropertyChanged event if not. </p>
  
  <p>And here is my code:</p>
  
  <pre><code>items.CollectionChanged += (object sender, NotifyCollectionChangedEventArgs e) =&gt;
  {
      foreach (var item in items.Where(o =&gt; o.PropertyChanged == null)) //error here
      {
          item.PropertyChanged += Item_PropertyChanged;
      }
  };
  </code></pre>
  
  <p>However, I'm getting a compilation error saying: </p>
  
  <blockquote>
    <p>The event 'ModelBase.PropertyChanged' can only appear on the left hand side of += or -=</p>
  </blockquote>
  
  <p>Any ideas how to check if an object has its PropertyChanged property event defined?</p>