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Tweak ScrollContentPresenter anchoring. 

Using WinUI's `ScrollPresenter` implementation to guide us.
pull/4814/head
Steven Kirk 6 years ago
parent
ce3c8316b5
commit
e9c990d908
1 changed files with 68 additions and 42 deletions
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  1. 110
      src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs

110
src/Avalonia.Controls/Presenters/ScrollContentPresenter.cs
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@ -16,6 +16,8 @@ namespace Avalonia.Controls.Presenters
/// </summary>
public class ScrollContentPresenter : ContentPresenter, IPresenter, IScrollable, IScrollAnchorProvider
{
private const double EdgeDetectionTolerance = 0.1;
/// <summary>
/// Defines the <see cref="CanHorizontallyScroll"/> property.
/// </summary>
@ -70,7 +72,9 @@ namespace Avalonia.Controls.Presenters
private Size _viewport;
private Dictionary<int, Vector>? _activeLogicalGestureScrolls;
private List<IControl>? _anchorCandidates;
private (IControl? control, Rect bounds) _anchor;
private IControl? _anchorElement;
private Rect _anchorElementBounds;
private bool _isAnchorElementDirty;
/// <summary>
/// Initializes static members of the <see cref="ScrollContentPresenter"/> class.
@ -138,7 +142,14 @@ namespace Avalonia.Controls.Presenters
}
/// <inheritdoc/>
IControl? IScrollAnchorProvider.CurrentAnchor => _anchor.control;
IControl? IScrollAnchorProvider.CurrentAnchor
{
get
{
EnsureAnchorElementSelection();
return _anchorElement;
}
}
/// <summary>
/// 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<IControl>();
_anchorCandidates.Add(element);
_isAnchorElementDirty = true;
}
/// <inheritdoc/>
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)

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