[iOS] Fixed KeepLastItemInView for CV1 and added support for KeepLastItemInView for CV2 #28720

kubaflo · 2025-03-31T23:22:39Z

Issues Fixed

Before	After
Screen.Recording.2025-04-01.at.01.17.56.mov	Screen.Recording.2025-04-01.at.01.15.22.mov

<Grid RowDefinitions="Auto, *">
    <Button Text="Add Item"
            Clicked="Button_Clicked"
            HorizontalOptions="Center"
            VerticalOptions="Center"/>
    <CollectionView ItemsUpdatingScrollMode="KeepLastItemInView"
                    Grid.Row="1"
                    x:Name="cv">
        <CollectionView.ItemTemplate>
            <DataTemplate>
                <Grid ColumnDefinitions="*,Auto">
                    <Label
                        Text="{Binding Text}"
                        HeightRequest="100"
                        VerticalOptions="Center"/>
                </Grid>
            </DataTemplate>
        </CollectionView.ItemTemplate>
    </CollectionView>
</Grid>

Copilot

Pull Request Overview

This PR adds support for the ItemsUpdatingScrollMode property "KeepLastItemInView" for CollectionView on iOS. Key changes include updating the LayoutFactory2 methods to accept the new parameter, modifying the custom UICollectionViewCompositionalLayout to enforce scrolling behavior, and updating the ItemsViewHandler2 and CollectionViewHandler2 to pass the new parameter.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Controls/src/Core/Handlers/Items2/iOS/LayoutFactory2.cs	Updated method signatures to include ItemsUpdatingScrollMode and added logic in the custom layout to scroll to the last item
src/Controls/src/Core/Handlers/Items2/ItemsViewHandler2.iOS.cs	Replaced the previous direct assignment with a call to UpdateLayout for propagating ItemsUpdatingScrollMode
src/Controls/src/Core/Handlers/Items2/CollectionViewHandler2.iOS.cs	Updated layout factory calls to pass the ItemsUpdatingScrollMode parameter

Comments suppressed due to low confidence (3)

src/Controls/src/Core/Handlers/Items2/iOS/LayoutFactory2.cs:12

The method signature now includes the new parameter 'itemsUpdatingScrollMode', which is a breaking change in the public API. Please ensure related documentation and tests are updated accordingly.

public static UICollectionViewLayout CreateList(LinearItemsLayout linearItemsLayout, LayoutGroupingInfo groupingInfo, LayoutHeaderFooterInfo headerFooterInfo, ItemsUpdatingScrollMode itemsUpdatingScrollMode)

src/Controls/src/Core/Handlers/Items2/ItemsViewHandler2.iOS.cs:120

Replacing the direct assignment of ItemsUpdatingScrollMode with an UpdateLayout() call may introduce side effects; ensure that tests cover the correct propagation of ItemsUpdatingScrollMode.

handler.UpdateLayout();

src/Controls/src/Core/Handlers/Items2/CollectionViewHandler2.iOS.cs:157

Ensure tests verify that the ItemsUpdatingScrollMode value is correctly propagated to the layout factory, including in fallback scenarios.

var itemsUpdatingScrollMode = ItemsView.ItemsUpdatingScrollMode;

Copilot · 2025-03-31T23:22:58Z

src/Controls/src/Core/Handlers/Items2/iOS/LayoutFactory2.cs

+		{
+			base.FinalizeCollectionViewUpdates();
+
+			if (_itemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepLastItemInView)


Overriding FinalizeCollectionViewUpdates to scroll to the last item is a significant behavior change; please ensure tests verify the accuracy of this scrolling behavior.

rmarinho · 2025-04-01T11:21:17Z

/azp run

azure-pipelines · 2025-04-01T11:21:37Z

Azure Pipelines successfully started running 3 pipeline(s).

rmarinho · 2025-04-01T11:23:06Z

src/Controls/src/Core/Handlers/Items2/iOS/LayoutFactory2.cs

+					}
+					else
+					{
+						collectionView.ScrollToItem(lastIndexPath, UICollectionViewScrollPosition.Right, true);


I wonder if we should look at RTL here

It turns out that the current implementation already supports RTL. I've included it in the UITest to be sure

rmarinho

Can we add a test ? Also can we make sure if RTL is on it scrolls correctly

Thanks

kubaflo · 2025-04-02T00:17:27Z

Can we add a test ? Also can we make sure if RTL is on it scrolls correctly

Thanks

sure!

rmarinho

Test is failing for Mac and CV1 KeepLastItemInViewShouldWork

https://dev.azure.com/xamarin/public/_build/results?buildId=139532&view=ms.vss-test-web.build-test-results-tab&runId=3999210&resultId=100081&paneView=debug

kubaflo · 2025-04-09T23:10:38Z

@rmarinho I've added a commit that fixes it for cv1

karthikraja-arumugam · 2025-04-11T11:15:14Z

This also fixes issue #18029

rmarinho · 2025-04-14T18:16:06Z

/azp run

azure-pipelines · 2025-04-14T18:16:26Z

Azure Pipelines successfully started running 3 pipeline(s).

PureWeen

test failure seems consistent
https://dev.azure.com/xamarin/public/_build/results?buildId=140014&view=ms.vss-test-web.build-test-results-tab&runId=4027466&resultId=100127&paneView=debug

LayoutPassesShouldNotIncrease

kubaflo · 2025-04-19T23:37:22Z

test failure seems consistent https://dev.azure.com/xamarin/public/_build/results?buildId=140014&view=ms.vss-test-web.build-test-results-tab&runId=4027466&resultId=100127&paneView=debug

LayoutPassesShouldNotIncrease

@albyrock87 I've modified your UI test. Could you please have a look at this pr and let me know if I should have modified the test?

albyrock87 · 2025-04-20T05:53:32Z

test failure seems consistent https://dev.azure.com/xamarin/public/_build/results?buildId=140014&view=ms.vss-test-web.build-test-results-tab&runId=4027466&resultId=100127&paneView=debug

LayoutPassesShouldNotIncrease

@albyrock87 I've modified your UI test. Could you please have a look at this pr and let me know if I should have modified the test?

Now my question is: you haven't touched 25671.xaml in any way, so how is it possible that the performance changed so much? 25671 is not using the flag you're fixing here, so I would expect no changes there.

Also, CV2 has a major performance decrease which seems even more strange.

Implements ItemsUpdatingScrollMode.KeepLastItemInView for CollectionView on iOS by updating layout creation and scroll logic. Adds internal ItemsUpdatingScrollMode property to ItemsLayout. Includes new test case and UI test for issue dotnet#28720 to verify correct behavior.

kubaflo · 2025-08-10T10:54:01Z

Closed in favour of #31104

Implements ItemsUpdatingScrollMode.KeepLastItemInView for CollectionView on iOS by updating layout creation and scroll logic. Adds internal ItemsUpdatingScrollMode property to ItemsLayout. Includes new test case and UI test for issue dotnet#28720 to verify correct behavior.

Copilot AI review requested due to automatic review settings March 31, 2025 23:22

kubaflo requested a review from a team as a code owner March 31, 2025 23:22

kubaflo requested review from StephaneDelcroix and rmarinho March 31, 2025 23:22

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kubaflo self-assigned this Mar 31, 2025

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PureWeen modified the milestones: .NET 9 SR6, .NET 9 SR7 Apr 8, 2025

rmarinho added the area-controls-collectionview CollectionView, CarouselView, IndicatorView label Apr 9, 2025

kubaflo changed the title ~~[iOS] Support for KeepLastItemInView for CV2~~ [iOS] Fixed KeepLastItemInView for CV1 and added support for KeepLastItemInView for CV2 Apr 9, 2025

rmarinho previously approved these changes Apr 14, 2025

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KeepLastItemInView not working on iOS #18029

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kubaflo dismissed rmarinho’s stale review via 78132f5 April 19, 2025 23:34

kubaflo force-pushed the cv2-KeepLastItemInView branch from 78132f5 to 12b4197 Compare April 19, 2025 23:40

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PureWeen modified the milestones: .NET 9 SR7, .NET 9 SR8 May 8, 2025

PureWeen modified the milestones: .NET 9 SR8, .NET 9 SR9 Jun 2, 2025

[iOS] support for KeepLastItemInView for CV2

ba5f11c

kubaflo force-pushed the cv2-KeepLastItemInView branch from 12b4197 to ba5f11c Compare June 3, 2025 14:45

prakashKannanSf3972 mentioned this pull request Jun 5, 2025

[Android] - Fix KeepScrollOffset Behavior During Dynamic Item Additions in CollectionView #29255

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4 tasks

SuthiYuvaraj mentioned this pull request Jun 9, 2025

Fix for Try scrolling down and when new items are added the first item does not kept in the displayed list. #27153

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PureWeen modified the milestones: .NET 9 SR9, .NET 9 SR10 Jul 3, 2025

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kubaflo closed this Aug 10, 2025

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[iOS] Fixed KeepLastItemInView for CV1 and added support for KeepLastItemInView for CV2 #28720

[iOS] Fixed KeepLastItemInView for CV1 and added support for KeepLastItemInView for CV2 #28720

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