// BringIntoView functionality is ported from WinUI ScrollPresenter
// https://github.com/microsoft/microsoft-ui-xaml/blob/main/dev/ScrollPresenter/ScrollPresenter.cpp
// with partial modifications to match the ScrollViewer control behavior.
protected override void OnBringIntoViewRequested(BringIntoViewRequestedEventArgs args)
{
base.OnBringIntoViewRequested(args);
UIElement content = RealContent as UIElement;
if (args.Handled ||
args.TargetElement == this ||
(args.TargetElement == content && content?.Visibility == Visibility.Collapsed) ||
!SharedHelpers.IsAncestor(args.TargetElement, this, true /*checkVisibility*/))
{
// Ignore the request when:
// - It was handled already.
// - The target element is this ScrollPresenter itself. A parent scrollPresenter may fulfill the request instead then.
// - The target element is effectively collapsed within the ScrollPresenter.
return;
}
Rect targetRect = new Rect();
double targetZoomedHorizontalOffset = 0.0;
double targetZoomedVerticalOffset = 0.0;
double appliedOffsetX = 0.0;
double appliedOffsetY = 0.0;
var viewportWidth = ViewportWidth;
var viewportHeight = ViewportHeight;
var zoomFactor = Scroller.ZoomFactor;
// Compute the target offsets based on the provided BringIntoViewRequestedEventArgs.
ComputeBringIntoViewTargetOffsets(
content,
args,
out targetZoomedHorizontalOffset,
out targetZoomedVerticalOffset,
out appliedOffsetX,
out appliedOffsetY,
out targetRect);
// Do not include the applied offsets so that potential parent bring-into-view contributors ignore that shift.
Rect nextTargetRect = new Rect(
targetRect.X * zoomFactor - targetZoomedHorizontalOffset - appliedOffsetX,
targetRect.Y * zoomFactor - targetZoomedVerticalOffset - appliedOffsetY,
Math.Min(targetRect.Width * zoomFactor, viewportWidth),
Math.Min(targetRect.Height * zoomFactor, viewportHeight));
Rect viewportRect = new Rect(
0.0f,
0.0f,
(float)viewportWidth,
(float)viewportHeight);
var verticalOffset = Scroller.VerticalOffset;
var horizontalOffset = Scroller.HorizontalOffset;
var zoomedVerticalOffset = verticalOffset;
var zoomedHorizontalOffset = horizontalOffset;
if (targetZoomedHorizontalOffset != zoomedHorizontalOffset ||
targetZoomedVerticalOffset != zoomedVerticalOffset)
{
Scroller.ChangeView(targetZoomedHorizontalOffset, targetZoomedVerticalOffset, zoomFactor, !args.AnimationDesired);
}
else
{
// No offset change was triggered because the target offsets are the same as the current ones. Mark the operation as completed immediately.
//RaiseViewChangeCompleted(true /*isForScroll*/, ScrollPresenterViewChangeResult::Completed, offsetsChangeCorrelationId);
}
if (SharedHelpers.DoRectsIntersect(nextTargetRect, viewportRect))
{
// Next bring a portion of this ScrollPresenter into view.
args.TargetRect = nextTargetRect;
args.TargetElement = Scroller;
args.HorizontalOffset = args.HorizontalOffset - appliedOffsetX;
args.VerticalOffset = args.VerticalOffset - appliedOffsetY;
}
else
{
// This ScrollPresenter did not even partially bring the TargetRect into its viewport.
// Mark the operation as handled since no portion of this ScrollPresenter needs to be brought into view.
args.Handled = true;
}
}