diff --git a/src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs b/src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs index 2a04558fc8..b0b52812b9 100644 --- a/src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs +++ b/src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs @@ -16,6 +16,8 @@ namespace Avalonia.Controls.Presenters /// public class ScrollContentPresenter : ContentPresenter, IPresenter, IScrollable, IScrollAnchorProvider { + private const double EdgeDetectionTolerance = 0.1; + /// /// Defines the property. /// @@ -70,7 +72,9 @@ namespace Avalonia.Controls.Presenters private Size _viewport; private Dictionary? _activeLogicalGestureScrolls; private List? _anchorCandidates; - private (IControl? control, Rect bounds) _anchor; + private IControl? _anchorElement; + private Rect _anchorElementBounds; + private bool _isAnchorElementDirty; /// /// Initializes static members of the class. @@ -138,7 +142,14 @@ namespace Avalonia.Controls.Presenters } /// - IControl? IScrollAnchorProvider.CurrentAnchor => _anchor.control; + IControl? IScrollAnchorProvider.CurrentAnchor + { + get + { + EnsureAnchorElementSelection(); + return _anchorElement; + } + } /// /// Attempts to bring a portion of the target visual into view by scrolling the content. @@ -215,16 +226,18 @@ namespace Avalonia.Controls.Presenters _anchorCandidates ??= new List(); _anchorCandidates.Add(element); + _isAnchorElementDirty = true; } /// void IScrollAnchorProvider.UnregisterAnchorCandidate(IControl element) { _anchorCandidates?.Remove(element); + _isAnchorElementDirty = true; - if (_anchor.control == element) + if (_anchorElement == element) { - _anchor = default; + _anchorElement = null; } } @@ -266,59 +279,69 @@ namespace Avalonia.Controls.Presenters // If we have an anchor and its position relative to Child has changed during the // arrange then that change wasn't just due to scrolling (as scrolling doesn't adjust // relative positions within Child). - if (_anchor.control != null && - TranslateBounds(_anchor.control, Child, out var updatedBounds) && - updatedBounds.Position != _anchor.bounds.Position) + if (_anchorElement != null && + TranslateBounds(_anchorElement, Child, out var updatedBounds) && + updatedBounds.Position != _anchorElementBounds.Position) { - var offset = updatedBounds.Position - _anchor.bounds.Position; + var offset = updatedBounds.Position - _anchorElementBounds.Position; return offset; } return default; } - // Calculate the new anchor element. - _anchor = CalculateCurrentAnchor(); + var isAnchoring = Offset.X >= EdgeDetectionTolerance || Offset.Y >= EdgeDetectionTolerance; - // Do the arrange. - ArrangeOverrideImpl(size, -Offset); + if (isAnchoring) + { + // Calculate the new anchor element if necessary. + EnsureAnchorElementSelection(); - // If the anchor moved during the arrange, we need to adjust the offset and do another arrange. - var anchorShift = TrackAnchor(); + // Do the arrange. + ArrangeOverrideImpl(size, -Offset); - if (anchorShift != default) - { - var newOffset = Offset + anchorShift; - var newExtent = Extent; - var maxOffset = new Vector(Extent.Width - Viewport.Width, Extent.Height - Viewport.Height); + // If the anchor moved during the arrange, we need to adjust the offset and do another arrange. + var anchorShift = TrackAnchor(); - if (newOffset.X > maxOffset.X) + if (anchorShift != default) { - newExtent = newExtent.WithWidth(newOffset.X + Viewport.Width); - } + var newOffset = Offset + anchorShift; + var newExtent = Extent; + var maxOffset = new Vector(Extent.Width - Viewport.Width, Extent.Height - Viewport.Height); - if (newOffset.Y > maxOffset.Y) - { - newExtent = newExtent.WithHeight(newOffset.Y + Viewport.Height); - } + if (newOffset.X > maxOffset.X) + { + newExtent = newExtent.WithWidth(newOffset.X + Viewport.Width); + } - Extent = newExtent; + if (newOffset.Y > maxOffset.Y) + { + newExtent = newExtent.WithHeight(newOffset.Y + Viewport.Height); + } - try - { - _arranging = true; - Offset = newOffset; - } - finally - { - _arranging = false; + Extent = newExtent; + + try + { + _arranging = true; + Offset = newOffset; + } + finally + { + _arranging = false; + } + + ArrangeOverrideImpl(size, -Offset); } - + } + else + { ArrangeOverrideImpl(size, -Offset); } Viewport = finalSize; Extent = Child.Bounds.Size.Inflate(Child.Margin); + _isAnchorElementDirty = true; return finalSize; } @@ -493,13 +516,17 @@ namespace Avalonia.Controls.Presenters } } - private (IControl, Rect) CalculateCurrentAnchor() + private void EnsureAnchorElementSelection() { - if (_anchorCandidates == null) + if (!_isAnchorElementDirty || _anchorCandidates is null) { - return default; + return; } + _anchorElement = null; + _anchorElementBounds = default; + _isAnchorElementDirty = false; + var bestCandidate = default(IControl); var bestCandidateDistance = double.MaxValue; @@ -526,10 +553,9 @@ namespace Avalonia.Controls.Presenters // bounds aren't relative to the ScrollContentPresenter itself, if they change // then we know it wasn't just due to scrolling. var unscrolledBounds = TranslateBounds(bestCandidate, Child); - return (bestCandidate, unscrolledBounds); + _anchorElement = bestCandidate; + _anchorElementBounds = unscrolledBounds; } - - return default; } private bool GetViewportBounds(IControl element, out Rect bounds)