title: Xamarin Forms - negate bool binding values
body: <p>I am learning the xamarin forms and mvvm pattern. I am wondering, if is it possible to negate binding bool value. What I mean is:</p>
  
  <p>I have, let's say Entry with isVisible Binding:</p>
  
  <pre><code>&lt;Entry
      x:Name="TextEntry"
      IsVisible="{Binding IsVisibleEntry}"
  /&gt;
  </code></pre>
  
  <p>and <code>Label</code> which i want to hide when <code>TextEntry</code> is visible.</p>
  
  <pre><code>&lt;Label x:Name="MainLabel" 
         isVisible="!{Binding IsVisibleEntry}"/&gt; //ofc it is not working
  </code></pre>
  
  <p>Is it possible to do without making a new variable for MainLabel in ViewModel?</p>