title: Set custom attached property on StoryBoard
body: <p>I have a storyboard and would like to set the attached property VisualStateUtility.InitialState.  I've tried various combinations, but the property never gets resolved.  </p>
  
  <p>I get the following error: <em>Cannot resolve TargetProperty (VisualStateUtility.InitialState)</em></p>
  
  <p><strong>How can I set the value of my custom attached property on the Storyboard?</strong></p>
  
  <pre><code>&lt;ObjectAnimationUsingKeyFrames Duration="0" Storyboard.TargetProperty="(Fully.Qualified.Namespace.VisualStateUtility.InitialState)"  Storyboard.TargetName="ExpanderButton"&gt;
  </code></pre>
  
  <p></p>
  
  <p></p>
  
  <pre><code>    public static string GetInitialState(DependencyObject obj)
      {
          return (string)obj.GetValue(InitialStateProperty);
      }
  
      public static void SetInitialState(DependencyObject obj, string value)
      {
          obj.SetValue(InitialStateProperty, value);
      }
  
      // Using a DependencyProperty as the backing store for InitialState.  This enables animation, styling, binding, etc...
      public static readonly DependencyProperty InitialStateProperty =
          DependencyProperty.RegisterAttached("InitialState", typeof(string), typeof(VisualStateUtility), new PropertyMetadata(null,OnInitialStatePropertyChanged));
  </code></pre>