Question

I often have to animate several things that do not belong to the view in wpf such as the volume of my computer or the position of the mouse. I will like to do so by using wpf storyboards and built in easing functions.

For example let’s say I want to use the following storyboard to animate (decrease volume) on my computer:

<Storyboard x:Key="Storyboard1">
        <DoubleAnimationUsingKeyFrames 
                     Storyboard.TargetProperty="someProperty"  
                     Storyboard.TargetName="SomeTarget">
            <EasingDoubleKeyFrame KeyTime="0:0:1" Value="0">
                <EasingDoubleKeyFrame.EasingFunction>
                    <CircleEase EasingMode="EaseOut"/>
                </EasingDoubleKeyFrame.EasingFunction>
            </EasingDoubleKeyFrame>
        </DoubleAnimationUsingKeyFrames>
</Storyboard>

and in my code behind I set the volume with the function:

  MyVolumeController.SetVolume(0);

---

as a result I will like to create a function that will look like: (note the function is some sort of pseudo code)

 public void AnimateProperty(Storyboard sb, Action<double> onPropertyChange)
 {
      var property = //sb.targetProperty;

      property.OnValueChanged += (a,b)=>{

           onPropertyChange(b.newValue);

      }

      sb.begin();// start animating

 }

then I would be able to animate the volume by calling that method as:

  AnimateProperty(
           (Storyboard)this.FindResource("Storyboard1"), // storyboard
           (newVal)=>{MyVolumeController.SetVolume(newVal) // action
  );

Answer 1

If you want to animate a property and get notified about value changes while the animation is running, you will have to make that property a dependency property, and attach a PropertyChangedCallback by dependency property metadata.

A typical declaration of such a dependency property would look like the code below (with double as property type here):

public class MyControl : ...
{
    public static readonly DependencyProperty SomethingProperty =
        DependencyProperty.Register(
            "Something", typeof(double), typeof(MyControl),
            new FrameworkPropertyMetadata(
                (o, e) => ((MyControl)o).SomethingChanged((double)e.NewValue)));

    public double Something
    {
        get { return (double)GetValue(SomethingProperty); }
        set { SetValue(SomethingProperty, value); }
    }

    private void SomethingChanged(double newValue)
    {
        // process value changes here
    }

    ...
}

Now you can easily animate this property, either by a Storyboard, or much simpler by applying an Animation directly:

DoubleAnimation animation = new DoubleAnimation
{
    To = ...,
    Duration = ...,
};

myControl.BeginAnimation(SomethingProperty, animation);