title: xamarin.forms binding from xaml to property
body: <p>I am a total newbie with bindings in xaml and I really don't get it sometimes.</p>
  
  <p>I have this in my xaml:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;ActivityIndicator IsRunning="{Binding IsLoading}" IsVisible="{Binding IsLoading}" /&gt;
  </code></pre>
  
  <p>The binding "IsLoading". Where do I declare/set this property?!</p>
  
  <p>My .cs looks like this:</p>
  
  <pre class="lang-cs prettyprint-override"><code>....
      public bool IsLoading;
  
      public CardsListXaml ()
      {
          InitializeComponent ();
          IsLoading = true;
   ....
  </code></pre>