title: Use of TypeCatalog
body: <p>I thought this would be easy, but after scanning many pages Google hasn't come to my aid.</p>
  
  <p>I have the following in a test method.</p>
  
  <pre><code>var tCatalog = new TypeCatalog(typeof (ISystemIndex));
  var aCatalog = new AssemblyCatalog(typeof (ISystemIndex).Assembly);
  </code></pre>
  
  <p><code>tCatalog.Parts</code> comes up empty, while <code>aCatalog.Parts.Count</code> is 3 (one of them comes from a class decorated with <code>[Export(typeof(ISystemIndex))]</code>, the other two from classes inheriting from a base w/ Export defined)</p>
  
  <p>What am I doing wrong? Do I need to initialize the <code>TypeCatalog</code> in some way?</p>
  
  <p>The problem I'm trying to solve is to create a catalog with a subset of the exportable classes in my assembly.</p>
  
  <p>Thanks in advance.</p>