title: "Element is already the child of another element."
body: <p>At first, this exception doesn't really make sense to me. Why shouldn't i be able to duplicate this object multiple times? but thats not the point:</p>
  
  <p>i use a List. Whenever i navigate to a site, it should do this:</p>
  
  <pre><code> (App.Current as App).recent.ForEach(x =&gt; container.Children.Add(x));
  </code></pre>
  
  <p>(container = another StackPanel)</p>
  
  <p>the first time, it works. afterwards, i get the exception displayed in the questiontitle. i already tried using a listbox, but i just got a ArgumentException. I think these exceptions have the same source, but i don't know what i'm doing wrong. please help</p>
  
  <p>thanks</p>