feat: `ItemCollectionTransition` by MartinZikmund · Pull Request #22960 · unoplatform/uno

MartinZikmund · 2026-04-03T08:12:06Z

GitHub Issue: closes #22904

PR Type: ✨ Feature

What is the current behavior? 🤔

Support for ItemCollectionTransition missing

What is the new behavior? 🚀

Support for ItemCollectionTransition added

PR Checklist ✅

Please check if your PR fulfills the following requirements:

📝 Commits must be following the Conventional Commits specification.
🧪 Added Runtime tests, UI tests, or a manual test sample for the changes have been added (for bug fixes / features) (if applicable)
📚 Docs have been added/updated which fit documentation template (for bug fixes / features)
🖼️ Validated PR Screenshots Compare Test Run results.
❗ Contains NO breaking changes

Other information ℹ️

Copilot

Pull request overview

This PR ports WinUI’s ItemCollectionTransition* type system into Uno, adding the core transition descriptor/progress/provider APIs plus a runtime test suite to validate expected add/remove/move transition behavior.

Changes:

Added ItemCollectionTransition, related enums, progress type, completed-event args, and the base ItemCollectionTransitionProvider implementation under UI/Xaml/Controls/Repeater/.
Updated generated stubs to defer to the new handwritten implementations.
Added runtime tests validating provider callbacks, filtering behavior, and TransitionCompleted semantics.

Reviewed changes

Copilot reviewed 7 out of 13 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionTriggers.cs	Adds `[Flags]` triggers enum used to describe why transitions occur.
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionOperation.cs	Adds operation enum (Add/Remove/Move) for transition classification.
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransition.cs	Adds transition descriptor object + `Start()`/`HasStarted`.
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProgress.cs	Adds progress object used to signal completion back to the provider.
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionCompletedEventArgs.cs	Adds event args for the provider’s `TransitionCompleted` event.
src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProvider.cs	Adds provider batching logic using `CompositionTarget.Rendering` and keep-alive timers.
src/Uno.UI/Generated/3.0.0.0/Microsoft.UI.Xaml.Controls/ItemCollectionTransition*.cs	Updates generated stubs to skip members now implemented in Uno sources.
src/Uno.UI.RuntimeTests/Tests/Microsoft_UI_Xaml_Controls/Given_ItemCollectionTransitionProvider.cs	Adds runtime tests for transition provider call patterns and completion event behavior.

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src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProvider.cs

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProgress.cs

...o.UI.RuntimeTests/Tests/Microsoft_UI_Xaml_Controls/Given_ItemCollectionTransitionProvider.cs

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProvider.cs

morning4coffe-dev

LGTM, lets just recheck with WinUI3 source please

unodevops · 2026-04-06T10:22:04Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22960/docs/index.html

Copilot

Pull request overview

Copilot reviewed 17 out of 23 changed files in this pull request and generated 4 comments.

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Copilot · 2026-04-06T10:48:14Z

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProvider.mux.cs

+			if (usesNewTransitionsBatch)
+			{
+				// Allocating a new array of ItemCollectionTransition with animations for this new batch.
+				_transitionsWithAnimationsMap[_transitionsBatch] = new List<ItemCollectionTransition>();
+			}
+
+			_transitionsWithAnimationsMap[_transitionsBatch].Add(transition);


QueueTransition can throw KeyNotFoundException when the first transition in a new batch is not animated: _transitionsWithAnimationsMap[_transitionsBatch] is only initialized when usesNewTransitionsBatch is true and the current transition is animated. If the first transition(s) are filtered out by ShouldAnimate, a later animated transition will attempt to .Add into a missing list. Initialize the list on-demand (e.g., TryGetValue/create) before adding, independent of usesNewTransitionsBatch.

Suggested change

if (usesNewTransitionsBatch)

{

// Allocating a new array of ItemCollectionTransition with animations for this new batch.

_transitionsWithAnimationsMap[_transitionsBatch] = new List<ItemCollectionTransition>();

}

_transitionsWithAnimationsMap[_transitionsBatch].Add(transition);

if (!_transitionsWithAnimationsMap.TryGetValue(_transitionsBatch, out var transitionsWithAnimations))

{

// Allocating a new array of ItemCollectionTransition with animations for this batch.

transitionsWithAnimations = new List<ItemCollectionTransition>();

_transitionsWithAnimationsMap[_transitionsBatch] = transitionsWithAnimations;

}

transitionsWithAnimations.Add(transition);

Copilot · 2026-04-06T10:48:14Z

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProvider.mux.cs

+	// Uno does not support cleanup via finalizers; consumers should call Dispose() or stop
+	// using the provider when done. The timers will be collected when the provider is GC'd.


The #if HAS_UNO note mentions consumers should call Dispose(), but ItemCollectionTransitionProvider does not implement IDisposable or expose Dispose. This is misleading API guidance; either remove the Dispose() mention or implement deterministic cleanup (stop timers + detach handlers).

Suggested change

// Uno does not support cleanup via finalizers; consumers should call Dispose() or stop

// using the provider when done. The timers will be collected when the provider is GC'd.

// Uno does not support this destructor-style cleanup. When the provider is no longer used,

// any associated timers become eligible for collection when the provider is GC'd.

Copilot · 2026-04-06T10:48:14Z

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProgress.h.mux.cs

+	private readonly ItemCollectionTransition _transition;
+
+	/// <summary>
+	/// Gets the ItemCollectionTransition whose animations are in progress.
+	/// </summary>
+	public ItemCollectionTransition Transition => _transition;


_transition is declared readonly, so it can never be cleared. This prevents making Complete() single-shot and also means ItemCollectionTransitionProgress will keep the transition/provider/element graph alive as long as the progress object is referenced. If you intend Complete() to be idempotent and release references, _transition needs to be mutable (or guarded via a separate completion flag + clearable reference).

Suggested change

private readonly ItemCollectionTransition _transition;

/// <summary>

/// Gets the ItemCollectionTransition whose animations are in progress.

/// </summary>

public ItemCollectionTransition Transition => _transition;

// The reference is intentionally mutable so completion logic can clear it and release the transition graph.

private ItemCollectionTransition? _transition;

/// <summary>

/// Gets the ItemCollectionTransition whose animations are in progress.

/// </summary>

public ItemCollectionTransition? Transition => _transition;

Copilot · 2026-04-06T10:48:15Z

src/Uno.UI/UI/Xaml/Controls/Repeater/ItemCollectionTransitionProgress.mux.cs

+	public void Complete()
+	{
+		if (_transition is not null)
+		{
+			var transitionProvider = _transition.OwningProvider();
+			transitionProvider?.NotifyTransitionCompleted(_transition);
+		}


Complete() is not idempotent: calling it multiple times will raise TransitionCompleted multiple times because _transition is never cleared/guarded. Add a single-shot guard (e.g., set the stored transition reference to null after the first call, or track a _completed flag) so completion is raised at most once and references can be released.

unodevops · 2026-04-06T11:04:27Z

🤖 Your WebAssembly Skia Sample App stage site is ready! Visit it here: https://unowasmprstaging.z20.web.core.windows.net/pr-22960/wasm-skia-net9/index.html

unodevops · 2026-04-06T11:14:00Z

🤖 Your Docs stage site is ready! Visit it here: https://unodocsprstaging.z13.web.core.windows.net/pr-22960/docs/index.html

Copilot AI review requested due to automatic review settings April 3, 2026 08:12

MartinZikmund self-assigned this Apr 3, 2026

MartinZikmund requested a review from morning4coffe-dev April 3, 2026 08:12

Copilot started reviewing on behalf of MartinZikmund April 3, 2026 08:12 View session

Copilot AI reviewed Apr 3, 2026

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morning4coffe-dev approved these changes Apr 3, 2026

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MartinZikmund added 4 commits April 6, 2026 11:42

feat: ItemCollectionTransition

88abebf

test: ItemCollectionTransition

6e3e06e

chore: Improve port accuracy

3567bbe

feat: Improve WinUI port skill

a171406

MartinZikmund force-pushed the dev/mazi/repeater-collection branch from a51ff01 to a171406 Compare April 6, 2026 09:54

chore: Disposable

bd888db

Copilot AI review requested due to automatic review settings April 6, 2026 10:45

Copilot started reviewing on behalf of MartinZikmund April 6, 2026 10:45 View session

Copilot AI reviewed Apr 6, 2026

View reviewed changes

-			if (usesNewTransitionsBatch)
-			{
-				// Allocating a new array of ItemCollectionTransition with animations for this new batch.
-				_transitionsWithAnimationsMap[_transitionsBatch] = new List<ItemCollectionTransition>();
-			}
-			_transitionsWithAnimationsMap[_transitionsBatch].Add(transition);
+			if (!_transitionsWithAnimationsMap.TryGetValue(_transitionsBatch, out var transitionsWithAnimations))
+			{
+				// Allocating a new array of ItemCollectionTransition with animations for this batch.
+				transitionsWithAnimations = new List<ItemCollectionTransition>();
+				_transitionsWithAnimationsMap[_transitionsBatch] = transitionsWithAnimations;
+			}
+			transitionsWithAnimations.Add(transition);

		// Uno does not support cleanup via finalizers; consumers should call Dispose() or stop
		// using the provider when done. The timers will be collected when the provider is GC'd.

Conversation

MartinZikmund commented Apr 3, 2026

PR Type: ✨ Feature

What is the current behavior? 🤔

What is the new behavior? 🚀

PR Checklist ✅

Other information ℹ️

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unodevops commented Apr 6, 2026

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