title: Cast an Explicit ObservableCollection
body: <p>I have an ObservableCollection of an object in C#.  This object implements an interface.  I would like to be able to convert the ObservableCollection of the object to an ObservableCollection of the interface without having to parse through the collection.</p>
  
  <p>So for example:</p>
  
  <p>I have an object "Guitar" which implements an interface called "IMusicalInstrument".  I bind an ObservableCollection of Guitar objects to MyListBox.  I want the following line of code to be able to convert listbox itemsSource to an ObservableCollection.</p>
  
  <pre><code>    ObservableCollection&lt;IMusicalInstrument&gt; InstrumentList = 
  (ObservableCollection&lt;IMusicalInstrument&gt;)MyListBox.ItemsSource;
  </code></pre>
  
  <p>Currently, that is giving me an InvalidCastException.</p>
  
  <p>Is there a way to accomplish this (without having to parse through the collection)?</p>
  
  <p>Thanks,
  Seth</p>