title: WPF - OnPropertyChanged for a property within a collection
body: <p>In a view model, I have a collection of items of type "ClassA" called "MyCollection".  ClassA has a property named "IsEnabled".</p>
  
  <pre><code>class MyViewModel 
  {
      List&lt;ClassA&gt; MyCollection { get; set; }
  
      class ClassA { public bool IsEnabled { get; set; } }
  }
  </code></pre>
  
  <p>My view has a datagrid which binds to MyCollection.  Each row has a button whose "IsEnabled" attribute is bound to the IsEnabled property of ClassA.</p>
  
  <p>When conditions in the view model change such that one particular item in the MyCollction list needs to bow be disabled, I set the IsEnabled property to false:</p>
  
  <pre><code>MyCollection[2].IsEnabled = false;
  </code></pre>
  
  <p>I now want to notify the View of this change with a OnPropertyChanged event, but I don't know how to reference a particular item in the collection.  </p>
  
  <pre><code>OnPropertyChanged("MyCollection");
  OnPropertyChanged("MyCollection[2].IsEnabled");
  </code></pre>
  
  <p>both do not work.</p>
  
  <p>How do I notify the View of this change?  Thanks!</p>