title: Adding two Binding in WPF
body: <p>I have been playing with wpf lately and got stuck at a point where I would like to use two, binding path values sum as the binding of a third control. I tried using value converter but to no success. Would appreciate if any one can guide me to the right path. </p>
  
  <p>Here is what I have so far:</p>
  
  <p>I have two encoders like</p>
  
  <pre><code>  &lt;my3:NVAngle Canvas.Left="400" Canvas.Top="610" BindableValueExtended="120" BindableValueRetracted="0" AnimationDuration="2" x:Name="nvAArm3Rotate" BindableValue="0" InvertExtendedTag="False" InvertRetractedTag="False"  /&gt;
    &lt;my3:NVAngle Canvas.Left="400" Canvas.Top="610" BindableValueExtended="50" BindableValueRetracted="0" AnimationDuration="2" x:Name="nvAArm2Rotate" BindableValue="0" InvertExtendedTag="False" InvertRetractedTag="False"  /&gt;
  </code></pre>
  
  <p>and I would like to rotate an image with an angle which is the sum of above two angle encoders. Something like: </p>
  
  <pre><code>&lt;Image Canvas.Left="100" Canvas.Top="200" Source="/Images/ExtraInter.png" Stretch="Fill" Width="117" Height="15" RenderTransformOrigin="0.95, 0.5"&gt;
     &lt;Image.RenderTransform&gt;
                  &lt;RotateTransform&gt;
                      &lt;RotateTransform.Angle&gt;
                          &lt;MultiBinding Converter="{StaticResource BundleArm3Full}"&gt;
                              &lt;Binding ElementName="nvABundleArm2Rotate" Path="BindableValue" /&gt;
                              &lt;Binding ElementName="nvABundleArm3Rotate" Path="BindableValue" /&gt;
                          &lt;/MultiBinding&gt;
                      &lt;/RotateTransform.Angle&gt;
                  &lt;/RotateTransform&gt;
                      &lt;!--120--&gt;
                  &lt;/Image.RenderTransform&gt;
  &lt;/Image&gt;
  </code></pre>
  
  <p>and my converter is: </p>
  
  <pre><code> public class MultipleBindingAddConverter : IMultiValueConverter
  {
      public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
      {
          var doubleValues = values.Cast&lt;double&gt;().ToArray();
  
          var resultSum = doubleValues.Sum().ToString();
  
          return resultSum;
      }
  
      public object[] ConvertBack(object value, Type[] targetTypes, object parameter, CultureInfo culture)
      {
          throw new NotImplementedException();
      }
  }
  </code></pre>
  
  <p>I still see no rotation of the Image although I can guarantee that the BindableValues are changing. Would appreciate any help.</p>
  
  <p>Thanks!</p>