title: Is it possible to mix OnIdiom and OnPlatform in XAML (Xamarin.Forms)?
body: <p>For UWP I need a different size for the width of a column in a <code>Grid</code>. Additionally, the value should be different on tablet and on smartphone.</p>
  
  <p>The following code crashes the app</p>
  
  <pre><code>&lt;ColumnDefinition&gt;
      &lt;ColumnDefinition.Width&gt;
          &lt;OnIdiom.Phone&gt;
              &lt;OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="100" /&gt;
          &lt;/OnIdiom.Phone&gt;
          &lt;OnIdiom.Tablet&gt;
              &lt;OnPlatform x:TypeArguments="GridLength" iOS="*" Android="*" WinPhone="200" /&gt;
          &lt;/OnIdiom.Tablet&gt;
      &lt;/ColumnDefinition.Width&gt;
  &lt;/ColumnDefinition&gt;
  </code></pre>
  
  <p>with</p>
  
  <blockquote>
    <p>Type OnIdiom.Phone not found in xmlns <a href="http://xamarin.com/schemas/2014/forms" rel="noreferrer">http://xamarin.com/schemas/2014/forms</a></p>
  </blockquote>
  
  <p>The code is in a <code>ViewCell</code>. So I can't use an additional <code>ResourceDictionary</code> and also <code>OnSizeAllocated()</code> is not available in the code behind file.</p>
  
  <p>Is it possible to use <code>OnIdiom</code> and <code>OnPlatform</code> together?</p>