[iOS] - Fixed the performance issue that occurred when updating the Spacing in CollectionView for both Vertical List and Grid layouts

[prakashKannanSf3972]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Root Cause

• SubscribeToItemsLayoutPropertyChanged subscribes to the PropertyChanged event to track changes in the layout.
• However, when the ItemsLayout is updated, new PropertyChanged event handlers are added without removing the previously registered handlers.
• This causes the number of event handlers to accumulate exponentially with each update.
• As a result, each layout change triggers multiple redundant calls to UpdateLayout(), causing cascading layout recalculations and severe performance degradation.

Description of Change

• Properly unsubscribed from ItemsLayout.PropertyChanged by invoking a dedicated cleanup method in DisconnectHandler() before the base disposal logic.
• Ensured existing event handlers are unsubscribed before assigning new ones in SubscribeToItemsLayoutPropertyChanged().

Tested the behaviour in the following platforms

• Android
• Windows
• iOS
• Mac

Issues Fixed

Fixes #27666
Fixes #27667
Fixes #29619

Output

Before	After
Before_Fix.mov	After_Fix.mov

[dotnet-policy-service]

Hey there @@prakashKannanSf3972! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsuarezruiz]

/azp run MAUI-UITests-public

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Copilot]

Pull Request Overview

This PR fixes a severe performance degradation in CollectionView updates by preventing the exponential accumulation of PropertyChanged event registrations. The key changes include unsubscribing existing event handlers before adding new ones, overriding DisconnectHandler to remove event handlers on disconnect, and updating the public API files to reflect these changes.

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue27666.cs	Added UI test verifying issue behavior
src/Controls/tests/TestCases.HostApp/Issues/Issue27666.cs	Updated HostApp test for CollectionView spacing update
src/Controls/src/Core/PublicAPI/net-maccatalyst/PublicAPI.Unshipped.txt	Updated public API with DisconnectHandler override
src/Controls/src/Core/PublicAPI/net-ios/PublicAPI.Unshipped.txt	Updated public API with DisconnectHandler override
src/Controls/src/Core/Handlers/Items2/CollectionViewHandler2.iOS.cs	Modified event handler subscription logic and added DisconnectHandler override

Comments suppressed due to low confidence (1)

src/Controls/tests/TestCases.HostApp/Issues/Issue27666.cs:91

• [nitpick] The UI test only triggers the spacing update without validating that the spacing has actually changed. Consider adding assertions to verify that the layout property is updated as expected.

void OnItemSpacingButtonClicked(object sender, EventArgs e)

[Copilot]

[nitpick] Consider extracting the magic numbers (50 and 20) into named constants to improve code maintainability and clarity.

Suggested change

	void OnItemSpacingButtonClicked(object sender, EventArgs e)
	{
	if (collectionView.ItemsLayout is LinearItemsLayout layout)
	{
	layout.ItemSpacing = layout.ItemSpacing == 0 ? 50 : 20;
	const double DefaultItemSpacing = 50;
	const double AlternateItemSpacing = 20;
	void OnItemSpacingButtonClicked(object sender, EventArgs e)
	{
	if (collectionView.ItemsLayout is LinearItemsLayout layout)
	{
	layout.ItemSpacing = layout.ItemSpacing == 0 ? DefaultItemSpacing : AlternateItemSpacing;

[Copilot]

The introduction of a new override for DisconnectHandler in the public API could constitute a breaking change. Please ensure that the public documentation is updated accordingly and that consumers are aware of this update.

[Copilot]

The introduction of a new override for DisconnectHandler in the public API could constitute a breaking change. Please ensure that the public documentation is updated accordingly and that consumers are aware of this update.

[jsuarezruiz]

The test RefreshShouldNotChangeSize is failing on iOS.
Snapshot different than baseline: RefreshShouldNotChangeSize.png (10.83% difference)

Could you verify if is related with the changes?

[prakashKannanSf3972]

The test RefreshShouldNotChangeSize is failing on iOS. Snapshot different than baseline: RefreshShouldNotChangeSize.png (10.83% difference)

Could you verify if is related with the changes?

@jsuarezruiz , The test RefreshShouldNotChangeSize is currently failing in the CI on iOS, however, the same test passes locally with both CV1 and CV2 handlers. Could you please re-run the CI to verify if the issue persists.

[PureWeen]

Let's review
#29638

[jsuarezruiz]

@prakashKannanSf3972 Could you rebase and fix the conflicts? Thanks in advance.

[prakashKannanSf3972]

@prakashKannanSf3972 Could you rebase and fix the conflicts? Thanks in advance.

@jsuarezruiz, The conflicts have been resolved. Thanks.

[PureWeen]

#29683