public class ParallaxBehavior : Behavior<FrameworkElement>
{ /// <summary>
/// Gets or sets the element that will parallax while scrolling.
/// </summary>
public UIElement ParallaxContent
{ get { return (UIElement)GetValue(ParallaxContentProperty); } set { SetValue(ParallaxContentProperty, value); } }
public static readonly DependencyProperty ParallaxContentProperty = DependencyProperty.Register(
"ParallaxContent",
typeof(UIElement),
typeof(ParallaxBehavior),
new PropertyMetadata(null, OnParallaxContentChanged));
/// <summary>
/// Gets or sets the rate at which the ParallaxContent parallaxes.
/// </summary>
public double ParallaxMultiplier
{ get { return (double)GetValue(ParallaxMultiplierProperty); } set { SetValue(ParallaxMultiplierProperty, value); } }
public static readonly DependencyProperty ParallaxMultiplierProperty = DependencyProperty.Register(
"ParallaxMultiplier",
typeof(double),
typeof(ParallaxBehavior),
new PropertyMetadata(0.3d));
protected override void OnAttached()
{ base.OnAttached();
AssignParallax();
}
private void AssignParallax()
{ if (ParallaxContent == null) return;
if (AssociatedObject == null) return;
var scroller = AssociatedObject as ScrollViewer;
if (scroller == null)
{ scroller = AssociatedObject.GetChildOfType<ScrollViewer>();
}
if (scroller == null) return;
CompositionPropertySet scrollerViewerManipulation = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(scroller);
Compositor compositor = scrollerViewerManipulation.Compositor;
ExpressionAnimation expression = compositor.CreateExpressionAnimation("ScrollManipululation.Translation.Y * ParallaxMultiplier");
expression.SetScalarParameter("ParallaxMultiplier", (float)ParallaxMultiplier); expression.SetReferenceParameter("ScrollManipululation", scrollerViewerManipulation);
Visual textVisual = ElementCompositionPreview.GetElementVisual(ParallaxContent);
textVisual.StartAnimation("Offset.Y", expression); }
private static void OnParallaxContentChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{ var b = d as ParallaxBehavior;
b.AssignParallax();
}
}