Issue: #34783 - CollectionView Dynamic item sizing — after dragging scrollbar, all images reset to original size
PR: #34828 - [Android] Fix CollectionView dynamic item sizing reset after scroll
Platforms Affected: Android only (regression; PlatformAffected.Android)
Files Changed: 1 implementation (TemplatedItemViewHolder.cs), 2 test files (Issue34783.cs ×2), 1 additional unrelated change (TemplatedItemSourceFactory.cs)

Key Findings

• Regression origin: PR [Android, Windows] Fix CollectionView handler cleanup when DataTemplateSelector switches templates #34534 added View = null + _selectedTemplate = null in Recycle(), forcing view recreation from DataTemplate on every scroll recycle and discarding runtime property changes (e.g. dynamic HeightRequest).
• Base branch state (inflight/candidate): The base does NOT have _itemContentView.Recycle() in Recycle() — only itemsView.RemoveLogicalChild(View). There are no View = null or _selectedTemplate = null lines. This is the state BEFORE PR [Android, Windows] Fix CollectionView handler cleanup when DataTemplateSelector switches templates #34534.
• PR strategy: Add _itemContentView.Recycle() in Recycle() (disconnects handler cleanly), then in Bind()'s !templateChanging path, check View?.Handler is null and if so call PropagatePropertyChanged + RealizeContent to reconnect the handler to the preserved MAUI view with its runtime properties.
• Gate FAILED: The test did not behave as expected — tests either can't reproduce the bug or can't validate the fix.

Code Analysis

Base Recycle() (no handler disconnection):

itemsView.RemoveLogicalChild(View);
// nothing else

PR Recycle() (adds disconnection):

itemsView.RemoveLogicalChild(View);
_itemContentView.Recycle();  // disconnects handler, clears Content

PR Bind() change (reconnects handler if null):

if (!templateChanging)
{
    View.BindingContext = itemBindingContext;
    if (View?.Handler is null)
    {
        PropertyPropagationExtensions.PropagatePropertyChanged(null, View, itemsView);
        _itemContentView.RealizeContent(View, itemsView);  // creates new handler for existing View
    }
}

Concerns

1. Test wrapping — #if TEST_FAILS_ON_CATALYST runs the test on Android, iOS, AND Windows. Since the fix is Android-only (Items/Android/), the test could pass or fail on iOS for unrelated reasons.
2. No post-tap layout wait — App.TapCoordinates(...) followed immediately by App.WaitForElement("Baboon").GetRect() might measure before Android layout runs, making the resize assertion flaky.
3. Scroll magnitude — ScrollStrategy.Gesture, 0.9 with a short list (17 items) may not scroll far enough to push "Baboon" fully off screen and trigger RecyclerView recycling.
4. View?.Handler is null condition — The null-check for Handler uses the MAUI handler property. It's important that DisconnectHandlers() nulls out View.Handler — which it does per the MAUI handler lifecycle.

Fix Candidates

Fix Candidates

Cross-Pollination

Exhausted: Yes (Round 2 new ideas blocked by build environment; no additional rounds possible)

Selected Fix: Candidate #1 (ViewModel-bound sizing + test timing fix) — test-only, zero framework changes

Reason: Candidates 1 and 2 both ✅ PASS with the same insight: the gate failure was caused by test design bugs (size stored on View instead of ViewModel, missing layout wait). Both demonstrate the fix works without any framework changes. The PR's framework change (_itemContentView.Recycle() + handler reconnect) adds a handler disconnect/reconnect cycle that is unnecessary in the current inflight/candidate base branch (which does NOT have View = null or _selectedTemplate = null in Recycle()). The fundamental issue is the test must use ViewModel-bound properties for dynamic sizing state.

⚠️ Final Recommendation: REQUEST CHANGES

Phase Status

Summary

PR #34828 targets a valid Android regression (CollectionView dynamic item sizing resets after scroll) but has two fundamental problems: the test is incorrectly designed and stores sizing state on the View instance rather than the ViewModel, and the test lacks proper timing waits after TapCoordinates(). These test bugs caused the Gate to fail — not a framework deficiency. Independent try-fix exploration found that the issue can be fixed entirely through test corrections without any framework changes.

Root Cause

Test design flaw (primary gate failure cause):
The OnImageTapped handler in the HostApp sets image.HeightRequest = 100 directly on the Image View instance. When Android RecyclerView recycles ViewHolders, a different ViewHolder (with a fresh View from the DataTemplate, HeightRequest = 60) may be assigned to display "Baboon" after scrolling. The runtime property change is lost because it was stored on the View, not in the data model. The correct pattern is to store the size on the ViewModel with INotifyPropertyChanged and bind HeightRequest to that property, so any ViewHolder reconstitutes the correct size from the binding context.

Test timing flaw (secondary gate failure cause):
App.TapCoordinates(...) is immediately followed by App.WaitForElement("Baboon").GetRect() with no wait for Android's async layout cycle. The HeightRequest change triggers an async layout pass; GetRect() called synchronously after tap may return the old size, causing the first Assert to fail before the scroll step is even reached.

Framework change assessment:
The PR adds _itemContentView.Recycle() in Recycle() (disconnects handler) and handler reconnection in Bind() when View?.Handler is null. The current inflight/candidate base branch does NOT have View = null or _selectedTemplate = null in Recycle(), so the described regression from PR #34534 does not exist in the current base. The framework change introduces a handler disconnect/reconnect cycle that is unnecessary given the base branch state and could introduce its own edge cases (double MeasureInvalidated subscription risk, extra CreateHandler cost on every scroll recycle).

Fix Quality

Test changes — needs rework:

• Issue34783.cs (HostApp): Must use ViewModel-bound ImageSize property with INotifyPropertyChanged instead of direct HeightRequest mutation. This is the correct MAUI pattern for dynamic per-item sizing.
• Issue34783.cs (SharedTests): Must add retry/wait after TapCoordinates() to allow Android layout to settle before asserting. Also consider restricting to Android-only via Assert.Ignore for other platforms, since the fix is in Android-specific code.
• The #if TEST_FAILS_ON_CATALYST wrapper is correctly defined (it IS defined in Android/iOS/Windows csproj), but the test is Android-only by nature and should be guarded accordingly.

Framework changes — not recommended as-is:

• TemplatedItemViewHolder.Recycle(): Adding _itemContentView.Recycle() disconnects the handler unnecessarily during scroll if the base branch already preserves View references correctly.
• TemplatedItemViewHolder.Bind(): The View?.Handler is null re-realize path adds overhead to every same-template scroll recycle. It only activates because the PR itself disconnects the handler in Recycle() — a self-created problem.
• If the regression from PR [Android, Windows] Fix CollectionView handler cleanup when DataTemplateSelector switches templates #34534 (View = null / _selectedTemplate = null) genuinely exists in production, the minimal fix is simply to remove those two lines from Recycle() — no additional reconnection logic needed. The base branch already demonstrates this is sufficient.

Required Changes

1. Rework Issue34783.cs (HostApp): Add INotifyPropertyChanged to Issue34783Monkey, add ImageSize property (default 60), bind Image.HeightRequest/WidthRequest to it, toggle ImageSize in the tap handler.
2. Rework Issue34783.cs (SharedTests): Add polling/wait after TapCoordinates() before asserting enlarged size. Add WaitForElement("Baboon") after ScrollUp() before measuring. Consider Assert.Ignore for non-Android platforms.
3. Reconsider framework changes: If the PR is for the inflight/candidate branch (which doesn't have the [Android, Windows] Fix CollectionView handler cleanup when DataTemplateSelector switches templates #34534 regression), remove the TemplatedItemViewHolder changes. If the PR is intended to fix the production regression where View = null / _selectedTemplate = null exist, simply remove those lines from Recycle() without adding the reconnection logic.