title: Bind size of ObservableList in Android Databinding
body: <p>How can I bind the size of an <code>ObservableList</code> in my view?<br>
  I´m using the databinding library with an <code>ObservableList</code> in my android app like this:</p>
  
  <pre><code>// ViewModel
  class ViewModel {
      ...
      public final ObservableList&lt;Item&gt; items = new ObservableList&lt;&gt;()
      ...
  }
  </code></pre>
  
  <p>and my View</p>
  
  <pre><code>// View
  &lt;layout&gt;
      &lt;data&gt;
          &lt;variable name="viewmodel" type="com.myapp.ViewModel" /&gt;
      &lt;/data&gt;
  
      &lt;TextView
          ...
          android:text="@{viewmodel.items.???}"
      /&gt;
  &lt;/layout&gt;
  </code></pre>
  
  <p>In the views <code>TextView</code> I want to show the size of the items-list. I tried to use <code>android:text="viewmodel.items.size</code> or <code>viewmodel.items.size()</code> but that doesn´t work. How can I do this?</p>