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Improve iOS CollectionView performance by leveraging the new platform level invalidation mechanism #28225

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Merged
merged 8 commits into from
Mar 25, 2025
Merged

Improve iOS CollectionView performance by leveraging the new platform level invalidation mechanism #28225

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fbb04bd
Use native invalidation mechanism to detect TemplatedCell size change.
albyrock87 Mar 6, 2025
10e4731
Updated tests and improved solution
albyrock87 Mar 6, 2025
025e9ad
Add support for resizing header and footer
albyrock87 Mar 10, 2025
0e6fecc
Fix CV1 invalidation
albyrock87 Mar 10, 2025
d569066
Fixes
albyrock87 Mar 11, 2025
edec326
Other fixes and addressing PR review
albyrock87 Mar 12, 2025
f8e5c54
Update layout passes based on CI run
albyrock87 Mar 16, 2025
27ac934
Merge branch 'main' into avoid-using-measure-invalidate-in-collection…
albyrock87 Mar 21, 2025
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1 change: 1 addition & 0 deletions src/Controls/src/Core/Handlers/Items/iOS/ItemsViewCell.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ protected void InitializeContentConstraints(UIView platformView)
ContentView.TrailingAnchor.ConstraintEqualTo(TrailingAnchor).Active = true;

// And we want the ContentView to be the same size as the root renderer for the Forms element
// TODO: we should probably remove this to support `Margin` applied to the cell's root `VirtualView`
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@rmarinho rmarinho Mar 25, 2025

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We should create a new issue for this, maybe for net10.0

ContentView.TopAnchor.ConstraintEqualTo(platformView.TopAnchor).Active = true;
ContentView.BottomAnchor.ConstraintEqualTo(platformView.BottomAnchor).Active = true;
ContentView.LeadingAnchor.ConstraintEqualTo(platformView.LeadingAnchor).Active = true;
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61 changes: 33 additions & 28 deletions src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs
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Expand Up @@ -29,6 +29,7 @@ public abstract class ItemsViewController<TItemsView> : UICollectionViewControll
protected ItemsViewLayout ItemsViewLayout { get; set; }

bool _initialized;
bool _laidOut;
bool _isEmpty = true;
bool _emptyViewDisplayed;
bool _disposed;
Expand Down Expand Up @@ -193,18 +194,48 @@ public override void LoadView()
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
ConstrainItemsToBounds();
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@albyrock87 albyrock87 Mar 7, 2025

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This makes no sense here because bounds are not set yet: they'll be in ViewWillLayoutSubviews.
So any computation made here cannot be trustworthy.

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@rmarinho rmarinho Mar 24, 2025

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If we navigate from a CV page to a new page and then back to the CV sometimes ViewWillLayoutSubviews will not always trigger.

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@albyrock87 albyrock87 Mar 25, 2025 •
edited
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Interesting, but why is it necessary to trigger this method again considering the view was already laid out before pushing the new page? @rmarinho

}

public override void ViewWillLayoutSubviews()
{
ConstrainItemsToBounds();

if (CollectionView is Items.MauiCollectionView { NeedsCellLayout: true } collectionView)
{
InvalidateLayoutIfItemsMeasureChanged();
collectionView.NeedsCellLayout = false;
}

base.ViewWillLayoutSubviews();
InvalidateMeasureIfContentSizeChanged();
LayoutEmptyView();

_laidOut = true;
}

void InvalidateLayoutIfItemsMeasureChanged()
{
var visibleCells = CollectionView.VisibleCells;
List<NSIndexPath> invalidatedPaths = null;

var visibleCellsLength = visibleCells.Length;
for (int n = 0; n < visibleCellsLength; n++)
{
if (visibleCells[n] is TemplatedCell { MeasureInvalidated: true } cell)
{
invalidatedPaths ??= new List<NSIndexPath>(visibleCellsLength);
var path = CollectionView.IndexPathForCell(cell);
invalidatedPaths.Add(path);
}
}

if (invalidatedPaths != null)
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@rmarinho rmarinho Mar 24, 2025

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Suggested change
if (invalidatedPaths != null)
if (invalidatedPaths is not null)

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@rmarinho rmarinho Mar 24, 2025

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or is null return here

{
var layoutInvalidationContext = new UICollectionViewFlowLayoutInvalidationContext();
layoutInvalidationContext.InvalidateItems(invalidatedPaths.ToArray());
CollectionView.CollectionViewLayout.InvalidateLayout(layoutInvalidationContext);
}
}

void MauiCollectionView.ICustomMauiCollectionViewDelegate.MovedToWindow(UIView view)
{
Expand Down Expand Up @@ -284,7 +315,7 @@ void ConstrainItemsToBounds()
{
var contentBounds = CollectionView.AdjustedContentInset.InsetRect(CollectionView.Bounds);
var constrainedSize = contentBounds.Size;
ItemsViewLayout.UpdateConstraints(constrainedSize);
ItemsViewLayout.UpdateConstraints(constrainedSize, !_laidOut);
}

void EnsureLayoutInitialized()
Expand Down Expand Up @@ -373,7 +404,6 @@ protected virtual void UpdateDefaultCell(DefaultCell cell, NSIndexPath indexPath

protected virtual void UpdateTemplatedCell(TemplatedCell cell, NSIndexPath indexPath)
{
cell.ContentSizeChanged -= CellContentSizeChanged;
cell.LayoutAttributesChanged -= CellLayoutAttributesChanged;

var bindingContext = ItemsSource[indexPath];
Expand All @@ -382,7 +412,6 @@ protected virtual void UpdateTemplatedCell(TemplatedCell cell, NSIndexPath index
if (_measurementCells != null && _measurementCells.TryGetValue(bindingContext, out TemplatedCell measurementCell))
{
_measurementCells.Remove(bindingContext);
measurementCell.ContentSizeChanged -= CellContentSizeChanged;
measurementCell.LayoutAttributesChanged -= CellLayoutAttributesChanged;
cell.UseContent(measurementCell);
}
Expand All @@ -391,7 +420,6 @@ protected virtual void UpdateTemplatedCell(TemplatedCell cell, NSIndexPath index
cell.Bind(ItemsView.ItemTemplate, ItemsSource[indexPath], ItemsView);
}

cell.ContentSizeChanged += CellContentSizeChanged;
cell.LayoutAttributesChanged += CellLayoutAttributesChanged;

ItemsViewLayout.PrepareCellForLayout(cell);
Expand All @@ -407,29 +435,6 @@ protected object GetItemAtIndex(NSIndexPath index)
return ItemsSource[index];
}

[UnconditionalSuppressMessage("Memory", "MEM0003", Justification = "Proven safe in test: CollectionViewTests.ItemsSourceDoesNotLeak")]
void CellContentSizeChanged(object sender, EventArgs e)
{
if (_disposed)
return;

if (!(sender is TemplatedCell cell))
{
return;
}

var visibleCells = CollectionView.VisibleCells;

for (int n = 0; n < visibleCells.Length; n++)
{
if (cell == visibleCells[n])
{
ItemsViewLayout?.InvalidateLayout();
return;
}
}
}

[UnconditionalSuppressMessage("Memory", "MEM0003", Justification = "Proven safe in test: CollectionViewTests.ItemsSourceDoesNotLeak")]
void CellLayoutAttributesChanged(object sender, LayoutAttributesChangedEventArgs args)
{
Expand Down
4 changes: 2 additions & 2 deletions src/Controls/src/Core/Handlers/Items/iOS/ItemsViewLayout.cs
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Expand Up @@ -104,9 +104,9 @@ protected virtual void HandlePropertyChanged(PropertyChangedEventArgs propertyCh
}
}

internal virtual bool UpdateConstraints(CGSize size)
internal virtual bool UpdateConstraints(CGSize size, bool forceUpdate = false)
{
if (size.IsCloseTo(_currentSize))
if (size.IsCloseTo(_currentSize) && !forceUpdate)
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@albyrock87 albyrock87 Mar 7, 2025

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When used as ContentPage.Content = new CollectionView() the _currentSize never changes so this code path was not hit on the first LayoutSubviews, leading to wrong preferredAttributes computation and bad cell positioning.
You can verify this on main by testing out Issue13203 where the text is being positioned in the middle behind the safe area instead of being left aligned.

{
return false;
}
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9 changes: 7 additions & 2 deletions src/Controls/src/Core/Handlers/Items/iOS/MauiCollectionView.cs
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Expand Up @@ -10,6 +10,9 @@ internal class MauiCollectionView : UICollectionView, IUIViewLifeCycleEvents, IP
bool _invalidateParentWhenMovedToWindow;

WeakReference<ICustomMauiCollectionViewDelegate>? _customDelegate;

internal bool NeedsCellLayout { get; set; }

public MauiCollectionView(CGRect frame, UICollectionViewLayout layout) : base(frame, layout)
{
}
Expand All @@ -27,10 +30,12 @@ void IPlatformMeasureInvalidationController.InvalidateAncestorsMeasuresWhenMoved

void IPlatformMeasureInvalidationController.InvalidateMeasure(bool isPropagating)
{
if (!isPropagating)
if (isPropagating)
{
SetNeedsLayout();
NeedsCellLayout = true;
}

SetNeedsLayout();
}

[UnconditionalSuppressMessage("Memory", "MEM0002", Justification = IUIViewLifeCycleEvents.UnconditionalSuppressMessage)]
Expand Down
54 changes: 16 additions & 38 deletions src/Controls/src/Core/Handlers/Items/iOS/StructuredItemsViewController.cs
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Expand Up @@ -31,16 +31,6 @@ internal override void Disconnect()
{
base.Disconnect();

if (_headerViewFormsElement is not null)
{
_headerViewFormsElement.MeasureInvalidated -= OnFormsElementMeasureInvalidated;
}

if (_footerViewFormsElement is not null)
{
_footerViewFormsElement.MeasureInvalidated -= OnFormsElementMeasureInvalidated;
}

_headerUIView = null;
_headerViewFormsElement = null;
_footerUIView = null;
Expand Down Expand Up @@ -86,27 +76,23 @@ protected override CGRect DetermineEmptyViewFrame()

public override void ViewWillLayoutSubviews()
{
base.ViewWillLayoutSubviews();

// This update is only relevant if you have a footer view because it's used to place the footer view
// based on the ContentSize so we just update the positions if the ContentSize has changed
if (_footerUIView != null)
var hasHeaderOrFooter = _footerViewFormsElement is not null || _headerViewFormsElement is not null;
if (hasHeaderOrFooter && CollectionView is MauiCollectionView { NeedsCellLayout: true } collectionView)
{
var emptyView = CollectionView.ViewWithTag(EmptyTag);

if (IsHorizontal)
if (_headerViewFormsElement is not null)
{
if (_footerUIView.Frame.X != ItemsViewLayout.CollectionViewContentSize.Width ||
_footerUIView.Frame.X < emptyView?.Frame.X)
UpdateHeaderFooterPosition();
RemeasureLayout(_headerViewFormsElement);
}
else

if (_footerViewFormsElement is not null)
{
if (_footerUIView.Frame.Y != ItemsViewLayout.CollectionViewContentSize.Height ||
_footerUIView.Frame.Y < (emptyView?.Frame.Y + emptyView?.Frame.Height))
UpdateHeaderFooterPosition();
RemeasureLayout(_footerViewFormsElement);
}

UpdateHeaderFooterPosition();
}

base.ViewWillLayoutSubviews();
}

internal void UpdateFooterView()
Expand All @@ -123,15 +109,13 @@ internal void UpdateHeaderView()
UpdateHeaderFooterPosition();
}


internal void UpdateSubview(object view, DataTemplate viewTemplate, nint viewTag, ref UIView uiView, ref VisualElement formsElement)
{
uiView?.RemoveFromSuperview();

if (formsElement != null)
{
ItemsView.RemoveLogicalChild(formsElement);
formsElement.MeasureInvalidated -= OnFormsElementMeasureInvalidated;
}

UpdateView(view, viewTemplate, ref uiView, ref formsElement);
Expand All @@ -150,7 +134,6 @@ internal void UpdateSubview(object view, DataTemplate viewTemplate, nint viewTag
if (formsElement != null)
{
RemeasureLayout(formsElement);
formsElement.MeasureInvalidated += OnFormsElementMeasureInvalidated;
}
else
{
Expand All @@ -176,7 +159,11 @@ void UpdateHeaderFooterPosition()
}

if (_footerUIView != null && (_footerUIView.Frame.X != ItemsViewLayout.CollectionViewContentSize.Width || emptyWidth > 0))
_footerUIView.Frame = new CoreGraphics.CGRect(ItemsViewLayout.CollectionViewContentSize.Width + emptyWidth, 0, footerWidth, CollectionView.Frame.Height);
{
_footerUIView.Frame = new CoreGraphics.CGRect(
ItemsViewLayout.CollectionViewContentSize.Width + emptyWidth, 0, footerWidth,
CollectionView.Frame.Height);
}

if (CollectionView.ContentInset.Left != headerWidth || CollectionView.ContentInset.Right != footerWidth)
{
Expand Down Expand Up @@ -249,14 +236,5 @@ protected override void HandleFormsElementMeasureInvalidated(VisualElement forms
var size = base.GetSize();
return new Size(size.Value.Width, size.Value.Height + (_headerUIView?.Frame.Height ?? 0) + (_footerUIView?.Frame.Height ?? 0));
}

internal void UpdateLayoutMeasurements()
{
if (_headerViewFormsElement != null)
HandleFormsElementMeasureInvalidated(_headerViewFormsElement);

if (_footerViewFormsElement != null)
HandleFormsElementMeasureInvalidated(_footerViewFormsElement);
}
}
}
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