title: How do I bind to Spinner.SelectedItem
body: <p>I would like to bind the selected text from a spinner to a string named SelectedRole in my ViewModel. This is what I did</p>
  
  <pre><code>this.Bind(ViewModel, vm =&gt; vm.SelectedRole, v =&gt; v.roleSpinner.SelectedItem.ToString());
  </code></pre>
  
  <p>However, I ran into an exception.</p>
  
  <pre><code>System.NotSupportedException: Index expressions are only supported with constants.
  </code></pre>