[.NET 11] [Android] Implemented material3 support for CarouselView

.github/instructions/collectionview-handler-detection.instructions.md

@@ -10,20 +10,35 @@ applyTo: "src/Controls/src/Core/Handlers/Items/**,src/Controls/src/Core/Handlers
 There are **TWO separate handler implementations**, but they apply to **different platforms**:
 
 1. **Items/** (`Handlers/Items/`) - Contains code for **ALL platforms** (Android, iOS, Windows, MacCatalyst, Tizen)
-2. **Items2/** (`Handlers/Items2/`) - Contains code for **iOS/MacCatalyst ONLY**
+2. **Items2/** (`Handlers/Items2/`) - Primarily the **iOS/MacCatalyst** path, **plus** the **Android CarouselView Material3** handler (see exception below)
 
 ### Platform-Specific Deprecation
 
 The deprecation of Items/ **only applies to iOS/MacCatalyst**:
 
-| Platform | Active Handler | Notes |
-|----------|----------------|-------|
-| **Android** | `Items/Android/` | **ONLY implementation** - Items2/ has no Android code |
-| **Windows** | `Items/` | **ONLY implementation** - Items2/ has no Windows code |
-| **iOS** | `Items2/iOS/` | Items/ iOS code is deprecated |
-| **MacCatalyst** | `Items2/iOS/` | Items/ MacCatalyst code is deprecated |
+| Platform        | Control                       | Active Handler                           | Notes                                                                       |
+| --------------- | ----------------------------- | ---------------------------------------- | --------------------------------------------------------------------------- |
+| **Android**     | CollectionView                | `Items/Android/`                         | **ONLY implementation**                                                     |
+| **Android**     | CarouselView (Material3)      | `Items2/` (`CarouselViewHandler2`)       | Material3-only; registered when `RuntimeFeature.IsMaterial3Enabled` is true |
+| **Android**     | CarouselView (non-Material3)  | `Items/Android/` (`CarouselViewHandler`) | Default when Material3 is disabled                                          |
+| **Windows**     | CollectionView / CarouselView | `Items/`                                 | **ONLY implementation** - Items2/ has no Windows code                       |
+| **iOS**         | CollectionView / CarouselView | `Items2/iOS/`                            | Items/ iOS code is deprecated                                               |
+| **MacCatalyst** | CollectionView / CarouselView | `Items2/iOS/`                            | Items/ MacCatalyst code is deprecated                                       |
 
-**CRITICAL**: Items2/ is **iOS/MacCatalyst only**. There is NO Items2/ code for Android or Windows.
+**CRITICAL**: Items2/ is **iOS/MacCatalyst only**, with **one Android exception**: the Android **CarouselView Material3** handler (`CarouselViewHandler2` + `CarouselViewHandler2.Android.cs`, `MauiCarouselRecyclerView2`, `CarouselViewAdapter2`). There is **no** Items2/ code for Android CollectionView, and **no** Items2/ code for Windows.
+
+### Android CarouselView Material3 Exception
+
+When `RuntimeFeature.IsMaterial3Enabled` is `true`, Android `CarouselView` is registered to
+`Items2.CarouselViewHandler2` (see `AppHostBuilderExtensions.AddControlsHandlers`). This handler
+lives in `Items2/` but has **Android-specific** code (`*.Android.cs` partials) that uses Material's
+`CarouselLayoutManager`. Its Android types subclass the shared `Items.*` base classes
+(`CarouselViewAdapter2 : Items.CarouselViewAdapter`, `MauiCarouselRecyclerView2 : Items.MauiCarouselRecyclerView`),
+so changes to the shared Android carousel base classes in `Items/Android/` can affect both handlers.
+
+- **Android CarouselView Material3 work** → `Items2/` (`CarouselViewHandler2.Android.cs` and friends)
+- **Android CarouselView non-Material3 work** → `Items/Android/` (`CarouselViewHandler`)
+- **Android CollectionView work** → `Items/Android/` (unchanged — no Items2 Android CollectionView)
 
 ---
 
@@ -32,8 +47,12 @@ The deprecation of Items/ **only applies to iOS/MacCatalyst**:
 ### Decision Tree by Platform
 
 ```
+Is the issue/PR for Android CarouselView with Material3 enabled?
+  YES → Work on Items2/ (CarouselViewHandler2 Android partials)
+  NO  → Continue...
+
 Is the issue/PR for Android or Windows?
-  YES → Work on Items/ (it's the ONLY implementation)
+  YES → Work on Items/ (it's the ONLY implementation for these)
   NO  → Continue...
 
 Is the issue/PR for iOS or MacCatalyst?
@@ -50,23 +69,27 @@ Check which handler directory the files are in:
 git diff <base-branch>..<pr-branch> --name-only | grep -i "handlers/items"
 
 # Look for path pattern:
-# - Contains "/Items/Android/" → Android (ONLY implementation, work here)
+# - Contains "/Items/Android/" → Android CollectionView, or non-Material3 CarouselView (work here)
+# - Contains "/Items2/*.Android.cs" → Android CarouselView Material3 (CarouselViewHandler2)
 # - Contains "/Items/Windows/" or ".Windows.cs" → Windows (ONLY implementation, work here)
 # - Contains "/Items2/iOS/" or "Items2/*.iOS.cs" → iOS/MacCatalyst (CURRENT)
 # - Contains "/Items/*.iOS.cs" (not Items2) → iOS (DEPRECATED, prefer Items2/)
 ```
 
 ### Default Behavior by Platform
 
-| Platform | Default Action |
-|----------|----------------|
-| **Android** | ✅ Work on `Items/Android/` - it's the only option |
-| **Windows** | ✅ Work on `Items/` Windows files - it's the only option |
-| **iOS/MacCatalyst** | ✅ Work on `Items2/` - Items/ is deprecated for iOS |
+| Platform                                  | Default Action                                                 |
+| ----------------------------------------- | -------------------------------------------------------------- |
+| **Android** (CollectionView)              | ✅ Work on `Items/Android/` - it's the only option             |
+| **Android** (CarouselView, Material3)     | ✅ Work on `Items2/` - `CarouselViewHandler2` Android partials |
+| **Android** (CarouselView, non-Material3) | ✅ Work on `Items/Android/` - `CarouselViewHandler`            |
+| **Windows**                               | ✅ Work on `Items/` Windows files - it's the only option       |
+| **iOS/MacCatalyst**                       | ✅ Work on `Items2/` - Items/ is deprecated for iOS            |
 
 ### When to Work on Items/ for iOS (Deprecated)
 
 Only work on Items/ iOS code when:
+
 - PR explicitly modifies Items/ iOS files
 - User explicitly requests changes to deprecated handlers
 - Maintaining backward compatibility for a specific fix
@@ -75,21 +98,30 @@ Only work on Items/ iOS code when:
 
 ## Quick Reference
 
-| Path Pattern | Platform | Status |
-|--------------|----------|--------|
-| `Handlers/Items/Android/` | Android | **ACTIVE** (only implementation) |
-| `Handlers/Items/*.Windows.cs` | Windows | **ACTIVE** (only implementation) |
-| `Handlers/Items2/iOS/` | iOS/MacCatalyst | **ACTIVE** (current) |
-| `Handlers/Items/*.iOS.cs` | iOS/MacCatalyst | **DEPRECATED** (use Items2/) |
+| Path Pattern                                  | Platform                                              | Status                              |
+| --------------------------------------------- | ----------------------------------------------------- | ----------------------------------- |
+| `Handlers/Items/Android/`                     | Android (CollectionView + non-Material3 CarouselView) | **ACTIVE**                          |
+| `Handlers/Items2/*.Android.cs` (CarouselView) | Android (CarouselView, Material3)                     | **ACTIVE** (`CarouselViewHandler2`) |
+| `Handlers/Items/*.Windows.cs`                 | Windows                                               | **ACTIVE** (only implementation)    |
+| `Handlers/Items2/iOS/`                        | iOS/MacCatalyst                                       | **ACTIVE** (current)                |
+| `Handlers/Items/*.iOS.cs`                     | iOS/MacCatalyst                                       | **DEPRECATED** (use Items2/)        |
 
 ---
 
 ## Common Mistakes to Avoid
 
-❌ **Wrong**: "Items/ is deprecated, so I should check if Items2/ needs the same Android fix"
-- Items2/ has NO Android code - there's nothing to check
+❌ **Wrong**: "Items2/ has NO Android code at all"
+
+- The Android **CarouselView Material3** handler (`CarouselViewHandler2`) lives in `Items2/` with `*.Android.cs` partials. Android **CollectionView** still has no Items2/ code.
+
+❌ **Wrong**: "This Android CollectionView fix should also go in Items2/"
+
+- Android CollectionView only exists in `Items/Android/`. Only Android **CarouselView Material3** is in Items2/.
+
+❌ **Wrong**: "This Android CarouselView fix goes in Items/Android/" (without checking Material3)
+
+- If the issue is Material3-specific, the active Android CarouselView handler is `Items2.CarouselViewHandler2`. Only the non-Material3 path lives in `Items/Android/`.
 
-❌ **Wrong**: "This Android fix should also go in Items2/"
-- Items2/ is iOS-only, Android code only exists in Items/
+✅ **Correct**: "This is an Android CollectionView issue, so I work in `Items/Android/` — the only Android CollectionView implementation"
 
-✅ **Correct**: "This is an Android-only issue, so I work in Items/Android/ which is the only Android implementation"
+✅ **Correct**: "This is an Android CarouselView Material3 issue, so I work in `Items2/` (`CarouselViewHandler2.Android.cs`)"

src/Controls/src/Core/Handlers/Items/Android/MauiCarouselRecyclerView.cs

@@ -45,12 +45,17 @@ public override bool OnInterceptTouchEvent(MotionEvent ev)
 
 		protected virtual bool IsHorizontal => (Carousel?.ItemsLayout)?.Orientation == ItemsLayoutOrientation.Horizontal;
 
+		// Subclasses backed by a layout manager that has no virtual-range concept
+		// (e.g. Material's CarouselLayoutManager) can override this to force the
+		// non-loop code paths regardless of the public Carousel.Loop value.
+		protected virtual bool IsLoopEnabled => Carousel?.Loop == true;
+
 		protected override int DetermineTargetPosition(ScrollToRequestEventArgs args)
 		{
 			if (args.Mode == ScrollToMode.Element)
 				return ItemsViewAdapter.GetPositionForItem(args.Item);
 
-			if (!Carousel.Loop)
+			if (!IsLoopEnabled)
 				return args.Index;
 
 			if (_carouselViewLoopManager == null)
@@ -64,7 +69,7 @@ protected override int DetermineTargetPosition(ScrollToRequestEventArgs args)
 
 		public override bool OnTouchEvent(MotionEvent e)
 		{
-			if (Carousel.Loop)
+			if (IsLoopEnabled)
 				_carouselViewLoopManager.CenterIfNeeded(this, IsHorizontal);
 
 			return base.OnTouchEvent(e);
@@ -189,7 +194,7 @@ public override void ScrollTo(ScrollToRequestEventArgs args)
 			if (position == -1)
 			{
 				_gotoPosition = -1;
-				if (Carousel.Loop)
+				if (IsLoopEnabled)
 					_carouselViewLoopManager.AddPendingScrollTo(args);
 
 				return;
@@ -254,7 +259,7 @@ void CollectionItemsSourceChanged(object sender, System.Collections.Specialized.
 				else if (removingLastElement)
 					carouselPosition = Carousel.Position - 1;
 
-				if (Carousel.Loop)
+				if (IsLoopEnabled)
 				{
 					UpdateAdapter();
 					ScrollToPosition(carouselPosition);
@@ -362,7 +367,7 @@ void UpdateInitialPosition()
 			else
 			{
 				position = Carousel.Position;
-				if (Carousel.Loop && position == 0)
+				if (IsLoopEnabled && position == 0)
 				{
 					itemCount = ItemsViewAdapter.ItemsSource.Count;
 				}
@@ -372,7 +377,7 @@ void UpdateInitialPosition()
 
 			SetCurrentItem(_oldPosition);
 
-			var index = Carousel.Loop ? LoopedPosition(itemCount) + _oldPosition : _oldPosition;
+			var index = IsLoopEnabled ? LoopedPosition(itemCount) + _oldPosition : _oldPosition;
 			ScrollHelper.JumpScrollToPosition(index, Microsoft.Maui.Controls.ScrollToPosition.Center);
 			_gotoPosition = -1;
 		}
@@ -471,7 +476,7 @@ void CarouselViewScrolled(object sender, ItemsViewScrolledEventArgs e)
 
 			_noNeedForScroll = false;
 			var index = e.CenterItemIndex;
-			if (Carousel?.Loop == true)
+			if (IsLoopEnabled)
 			{
 				index = GetCarouselViewCurrentIndex(index);
 			}
@@ -535,7 +540,12 @@ void IMauiCarouselRecyclerView.UpdateFromCurrentItem()
 
 		void IMauiCarouselRecyclerView.UpdateFromPosition()
 		{
-			if (!_initialized)
+			// Only queue the initial-position pending scroll when looping is enabled: the queue
+			// is exclusively drained from loop-gated paths (LayoutReady and the scroll listener),
+			// so enqueuing it in the non-loop case (e.g. MauiCarouselRecyclerView2, or Loop=false)
+			// would leave a stale entry that is never flushed. The non-loop initial position is
+			// applied via the ScrollToItemPosition path below (and UpdateInitialPosition).
+			if (!_initialized && IsLoopEnabled)
 			{
 				_carouselViewLoopManager.AddPendingScrollTo(new ScrollToRequestEventArgs(Carousel.Position, -1, Microsoft.Maui.Controls.ScrollToPosition.Center, false));
 			}
@@ -602,7 +612,7 @@ void LayoutReady()
 			if (!_initialized)
 			{
 				ItemsView.Scrolled += CarouselViewScrolled;
-				if (Carousel.Loop)
+				if (IsLoopEnabled)
 				{
 					_carouselViewLoopManager.CenterIfNeeded(this, IsHorizontal);
 					_carouselViewLoopManager.CheckPendingScrollToEvents(this);

src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs

@@ -313,7 +313,6 @@ public virtual void UpdateLayoutManager()
 
 		protected virtual RecyclerViewScrollListener<TItemsView, TItemsViewSource> CreateScrollListener() => new(ItemsView, ItemsViewAdapter);
 
-
 		protected virtual void UpdateSnapBehavior()
 		{
 			_snapManager = GetSnapManager();