title: web api json deserialization failure
body: <p>I have a request endpoint using in web api:</p>
  
  <pre><code> public HttpResponseMessage Create(IList&lt;SlideContent&gt; l)
      {
          ...
      }
  </code></pre>
  
  <p>i send the parameter as a json and web api serializes it to IList</p>
  
  <p>SlideContent is:</p>
  
  <pre><code>public abstract class SlideItem
      {
         ...
      }
  </code></pre>
  
  <p>and i have specialised classes</p>
  
  <pre><code>    public class TitleSlideItem : SlideItem
      {
          ...
      }
  
  
      public class ParagraphSlideItem : SlideItem
      {
         ...
      }
  </code></pre>
  
  <p>just like that i can't call the Create function, because i get a </p>
  
  <blockquote>
    <p>missingmethodexception: cannot create abstract class</p>
  </blockquote>
  
  <p>so i can't deserialize the json parameter. if i remove the abstract modifier, then i don't have specialized objects, every object's type will be <code>SlideContent</code>.
  I even put annotations in the json, but it doesn't help either.</p>
  
  <p>If i'm not wrong, the i would have to write a custom binder for the abstract class, but how can i do that?</p>
  
  <p>Sincerely,</p>
  
  <p>Zoli</p>