/// <summary>
/// Uses Composition API to get the UIElement and sets an ExpressionAnimation
/// The ExpressionAnimation uses the height of the UIElement to calculate an opacity value
/// for the Header as it is scrolling off-screen. The opacity reaches 0 when the Header
/// is entirely scrolled off.
/// </summary>
/// <returns><c>true</c> if the assignment was successful; otherwise, <c>false</c>.</returns>
private bool AssignAnimation()
{
StopAnimation();
if (AssociatedObject == null)
{
return(false);
}
if (_scrollViewer == null)
{
_scrollViewer = AssociatedObject as ScrollViewer ?? AssociatedObject.FindDescendant <ScrollViewer>();
}
if (_scrollViewer == null)
{
return(false);
}
var listView = AssociatedObject as ListViewBase ?? AssociatedObject.FindDescendant <ListViewBase>();
if (listView != null && listView.ItemsPanelRoot != null)
{
Canvas.SetZIndex(listView.ItemsPanelRoot, -1);
}
if (_scrollProperties == null)
{
_scrollProperties = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(_scrollViewer);
}
if (_scrollProperties == null)
{
return(false);
}
// Implicit operation: Find the Header object of the control if it uses ListViewBase
if (HeaderElement == null && listView != null)
{
HeaderElement = listView.Header as UIElement;
}
var headerElement = HeaderElement as FrameworkElement;
if (headerElement == null || headerElement.RenderSize.Height == 0)
{
return(false);
}
if (_headerVisual == null)
{
_headerVisual = ElementCompositionPreview.GetElementVisual(headerElement);
}
if (_headerVisual == null)
{
return(false);
}
headerElement.SizeChanged -= ScrollHeader_SizeChanged;
headerElement.SizeChanged += ScrollHeader_SizeChanged;
_scrollViewer.GotFocus -= ScrollViewer_GotFocus;
_scrollViewer.GotFocus += ScrollViewer_GotFocus;
var compositor = _scrollProperties.Compositor;
if (_animationProperties == null)
{
_animationProperties = compositor.CreatePropertySet();
_animationProperties.InsertScalar("OffsetY", 0.0f);
}
var propSetOffset = _animationProperties.GetReference().GetScalarProperty("OffsetY");
var scrollPropSet = _scrollProperties.GetSpecializedReference <ManipulationPropertySetReferenceNode>();
var expressionAnimation = ExpressionFunctions.Max(propSetOffset - scrollPropSet.Translation.Y, 0);
_headerVisual.StartAnimation("Offset.Y", expressionAnimation);
// Mod: clip items panel below header
var itemsPanel = listView.ItemsPanelRoot;
if (itemsPanel == null)
{
return(true);
}
if (_itemsPanelVisual == null)
{
_itemsPanelVisual = ElementCompositionPreview.GetElementVisual(itemsPanel);
_contentClip = compositor.CreateInsetClip();
_itemsPanelVisual.Clip = _contentClip;
}
var expressionClipAnimation = ExpressionFunctions.Max(-scrollPropSet.Translation.Y, 0);
_contentClip.TopInset = (float)System.Math.Max(-_scrollViewer.VerticalOffset, 0);
_contentClip.StartAnimation("TopInset", expressionClipAnimation);
return(true);
}
/// <summary>
/// Uses Composition API to get the UIElement and sets an ExpressionAnimation
/// The ExpressionAnimation uses the height of the UIElement to calculate an opacity value
/// for the Header as it is scrolling off-screen. The opacity reaches 0 when the Header
/// is entirely scrolled off.
/// </summary>
/// <returns><c>true</c> if the assignment was successful; otherwise, <c>false</c>.</returns>
private bool AssignAnimation()
{
StopAnimation();
if (AssociatedObject == null)
{
return(false);
}
if (_scrollViewer == null)
{
_scrollViewer = AssociatedObject as ScrollViewer ?? AssociatedObject.FindDescendant <ScrollViewer>();
}
if (_scrollViewer == null)
{
return(false);
}
var listView = AssociatedObject as Windows.UI.Xaml.Controls.ListViewBase ?? AssociatedObject.FindDescendant <Windows.UI.Xaml.Controls.ListViewBase>();
if (listView != null && listView.ItemsPanelRoot != null)
{
Canvas.SetZIndex(listView.ItemsPanelRoot, -1);
}
if (_scrollProperties == null)
{
_scrollProperties = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(_scrollViewer);
}
if (_scrollProperties == null)
{
return(false);
}
// Implicit operation: Find the Header object of the control if it uses ListViewBase
if (HeaderElement == null && listView != null)
{
HeaderElement = listView.Header as UIElement;
}
var headerElement = HeaderElement as FrameworkElement;
if (headerElement == null || headerElement.RenderSize.Height == 0)
{
return(false);
}
if (_headerVisual == null)
{
_headerVisual = ElementCompositionPreview.GetElementVisual(headerElement);
}
if (_headerVisual == null)
{
return(false);
}
_scrollViewer.ViewChanged -= ScrollViewer_ViewChanged;
_scrollViewer.ViewChanged += ScrollViewer_ViewChanged;
_scrollViewer.GotFocus -= ScrollViewer_GotFocus;
_scrollViewer.GotFocus += ScrollViewer_GotFocus;
headerElement.SizeChanged -= ScrollHeader_SizeChanged;
headerElement.SizeChanged += ScrollHeader_SizeChanged;
var compositor = _scrollProperties.Compositor;
if (_animationProperties == null)
{
_animationProperties = compositor.CreatePropertySet();
_animationProperties.InsertScalar("OffsetY", 0.0f);
}
var propSetOffset = _animationProperties.GetReference().GetScalarProperty("OffsetY");
var scrollPropSet = _scrollProperties.GetSpecializedReference <ManipulationPropertySetReferenceNode>();
var expressionAnimation = ExpressionFunctions.Max(ExpressionFunctions.Min(propSetOffset, -scrollPropSet.Translation.Y), 0);
_headerVisual.StartAnimation("Offset.Y", expressionAnimation);
return(true);
}
private void Page_Loaded(object sender, RoutedEventArgs e)
{
// Retrieve the ScrollViewer that the GridView is using internally
var scrollViewer = gridView.GetFirstDescendantOfType <ScrollViewer>();
// Update the ZIndex of the header container so that the header is above the items when scrolling
var headerPresenter = (UIElement)VisualTreeHelper.GetParent((UIElement)gridView.Header);
var headerContainer = (UIElement)VisualTreeHelper.GetParent(headerPresenter);
Canvas.SetZIndex((UIElement)headerContainer, 1);
// Get the PropertySet that contains the scroll values from the ScrollViewer
_scrollerPropertySet = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(scrollViewer);
_compositor = _scrollerPropertySet.Compositor;
// Create a PropertySet that has values to be referenced in the ExpressionAnimations below
_props = _compositor.CreatePropertySet();
_props.InsertScalar("progress", 0);
_props.InsertScalar("clampSize", 150);
_props.InsertScalar("scaleFactor", 0.7f);
// Get references to our property sets for use with ExpressionNodes
var scrollingProperties = _scrollerPropertySet.GetSpecializedReference <ManipulationPropertySetReferenceNode>();
var props = _props.GetReference();
var progressNode = props.GetScalarProperty("progress");
var clampSizeNode = props.GetScalarProperty("clampSize");
var scaleFactorNode = props.GetScalarProperty("scaleFactor");
// Create a blur effect to be animated based on scroll position
var blurEffect = new GaussianBlurEffect()
{
Name = "blur",
BlurAmount = 0.0f,
BorderMode = EffectBorderMode.Hard,
Optimization = EffectOptimization.Balanced,
Source = new CompositionEffectSourceParameter("source")
};
var blurBrush = _compositor.CreateEffectFactory(
blurEffect,
new[] { "blur.BlurAmount" })
.CreateBrush();
blurBrush.SetSourceParameter("source", _compositor.CreateBackdropBrush());
// Create a Visual for applying the blur effect
_blurredBackgroundImageVisual = _compositor.CreateSpriteVisual();
_blurredBackgroundImageVisual.Brush = blurBrush;
_blurredBackgroundImageVisual.Size = new Vector2((float)OverlayRectangle.ActualWidth, (float)OverlayRectangle.ActualHeight);
// Insert the blur visual at the right point in the Visual Tree
ElementCompositionPreview.SetElementChildVisual(OverlayRectangle, _blurredBackgroundImageVisual);
// Create and start an ExpressionAnimation to track scroll progress over the desired distance
ExpressionNode progressAnimation = EF.Clamp(-scrollingProperties.Translation.Y / clampSizeNode, 0, 1);
_props.StartAnimation("progress", progressAnimation);
// Create and start an ExpressionAnimation to animate blur radius between 0 and 15 based on progress
ExpressionNode blurAnimation = EF.Lerp(0, 15, progressNode);
_blurredBackgroundImageVisual.Brush.Properties.StartAnimation("blur.BlurAmount", blurAnimation);
// Get the backing visual for the header so that its properties can be animated
Visual headerVisual = ElementCompositionPreview.GetElementVisual(Header);
// Create and start an ExpressionAnimation to clamp the header's offset to keep it onscreen
ExpressionNode headerTranslationAnimation = EF.Conditional(progressNode < 1, 0, -scrollingProperties.Translation.Y - clampSizeNode);
headerVisual.StartAnimation("Offset.Y", headerTranslationAnimation);
// Create and start an ExpressionAnimation to scale the header during overpan
ExpressionNode headerScaleAnimation = EF.Lerp(1, 1.25f, EF.Clamp(scrollingProperties.Translation.Y / 50, 0, 1));
headerVisual.StartAnimation("Scale.X", headerScaleAnimation);
headerVisual.StartAnimation("Scale.Y", headerScaleAnimation);
//Set the header's CenterPoint to ensure the overpan scale looks as desired
headerVisual.CenterPoint = new Vector3((float)(Header.ActualWidth / 2), (float)Header.ActualHeight, 0);
// Get the backing visual for the photo in the header so that its properties can be animated
Visual photoVisual = ElementCompositionPreview.GetElementVisual(BackgroundRectangle);
// Create and start an ExpressionAnimation to opacity fade out the image behind the header
ExpressionNode imageOpacityAnimation = 1 - progressNode;
photoVisual.StartAnimation("opacity", imageOpacityAnimation);
// Get the backing visual for the profile picture visual so that its properties can be animated
Visual profileVisual = ElementCompositionPreview.GetElementVisual(ProfileImage);
// Create and start an ExpressionAnimation to scale the profile image with scroll position
ExpressionNode scaleAnimation = EF.Lerp(1, scaleFactorNode, progressNode);
profileVisual.StartAnimation("Scale.X", scaleAnimation);
profileVisual.StartAnimation("Scale.Y", scaleAnimation);
// Get backing visuals for the text blocks so that their properties can be animated
Visual blurbVisual = ElementCompositionPreview.GetElementVisual(Blurb);
Visual subtitleVisual = ElementCompositionPreview.GetElementVisual(SubtitleBlock);
Visual moreVisual = ElementCompositionPreview.GetElementVisual(MoreText);
// Create an ExpressionAnimation that moves between 1 and 0 with scroll progress, to be used for text block opacity
ExpressionNode textOpacityAnimation = EF.Clamp(1 - (progressNode * 2), 0, 1);
// Start opacity and scale animations on the text block visuals
blurbVisual.StartAnimation("Opacity", textOpacityAnimation);
blurbVisual.StartAnimation("Scale.X", scaleAnimation);
blurbVisual.StartAnimation("Scale.Y", scaleAnimation);
subtitleVisual.StartAnimation("Opacity", textOpacityAnimation);
subtitleVisual.StartAnimation("Scale.X", scaleAnimation);
subtitleVisual.StartAnimation("Scale.Y", scaleAnimation);
moreVisual.StartAnimation("Opacity", textOpacityAnimation);
moreVisual.StartAnimation("Scale.X", scaleAnimation);
moreVisual.StartAnimation("Scale.Y", scaleAnimation);
// Get the backing visuals for the text and button containers so that their properites can be animated
Visual textVisual = ElementCompositionPreview.GetElementVisual(TextContainer);
Visual buttonVisual = ElementCompositionPreview.GetElementVisual(ButtonPanel);
// When the header stops scrolling it is 150 pixels offscreen. We want the text header to end up with 50 pixels of its content
// offscreen which means it needs to go from offset 0 to 100 as we traverse through the scrollable region
ExpressionNode contentOffsetAnimation = progressNode * 100;
textVisual.StartAnimation("Offset.Y", contentOffsetAnimation);
ExpressionNode buttonOffsetAnimation = progressNode * -100;
buttonVisual.StartAnimation("Offset.Y", buttonOffsetAnimation);
}
