[iOS] Fix HEIC images picked via PickPhotosAsync not displayed

[HarishwaranVijayakumar]

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!

Issue Details

• HEIC images picked via PickPhotosAsync are not displayed — the image appears blank, whereas other image formats (e.g., JPEG, PNG) display correctly.

Root Cause of the issue

• PR 34250 moved CompletedHandler invocation into the DismissViewController completion callback. This introduced a GC race condition where PhotoPickerPresentationControllerDelegate.Dispose() fires tcs.TrySetResult([]) before the async CompletedHandler finishes HEIC transcoding.
• HEIC is particularly affected because NSItemProvider.LoadDataRepresentationAsync transcoding is significantly slower than JPEG/PNG loading, widening the GC window.

Description of Change

Race condition prevention:

• In PhotoPickerDelegate.DidFinishPicking, the Handler property of PhotoPickerPresentationControllerDelegate is set to null before dismissing the picker to avoid a garbage collection race condition that could interfere with the async completion handler, especially during slow operations like HEIC transcoding.

Issues Fixed

Fixes #34953

Tested the behaviour in the following platforms

• - Windows
• - Android
• - iOS
• - Mac

Before	After
Before_.34786.mov	After_.34786.mov

[dotnet-policy-service]

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

[MauiBot]

🚦 Gate — Test Before and After Fix

👋 @HarishwaranVijayakumar — new gate results are available. Please review the latest session below.

🚦 Gate Session — 45a573b · Add fix · 2026-04-15 10:25 UTC

---

Gate Result: ⚠️ SKIPPED

No tests were detected in this PR.

Recommendation: Add tests to verify the fix using the write-tests-agent:

@copilot write tests for this PR

The agent will analyze the issue, determine the appropriate test type (UI test, device test, unit test, or XAML test), and create tests that verify the fix.

---

[MauiBot]

🤖 AI Summary

👋 @HarishwaranVijayakumar — new AI review results are available. Please review the latest session below.

📊 Review Session — 45a573b · Add fix · 2026-04-15 10:50 UTC

---

🔍 Pre-Flight — Context & Validation

---

Issue: #34953 - [iOS] [Regression] HEIC images picked via PickPhotosAsync not displayed
PR: #34954 - [iOS] Fix HEIC images picked via PickPhotosAsync not displayed
Platforms Affected: iOS only
Files Changed: 1 implementation (src/Essentials/src/MediaPicker/MediaPicker.ios.cs), 0 test

Key Findings

• Regression introduced by PR [iOS] Fix: invoke MediaPicker completion handler after DismissViewController #34250 which moved CompletedHandler invocation into the DismissViewController completion callback
• PhotoPickerPresentationControllerDelegate has a Handler property set to () => tcs.TrySetResult([]) (line 237) — meant for user-swipe-cancel scenarios
• Both DidDismiss and Dispose on PhotoPickerPresentationControllerDelegate invoke Handler
• GC can collect PhotoPickerPresentationControllerDelegate and fire Dispose → Handler?.Invoke() → tcs.TrySetResult([]) BEFORE the async CompletedHandler finishes HEIC transcoding (LoadDataRepresentationAsync is slow for HEIC)
• HEIC transcoding is significantly slower than JPEG/PNG, widening the GC race window
• Fix: null out pd.Handler in DidFinishPicking before calling DismissViewController, so that when Dispose fires it cannot call TrySetResult([]) prematurely
• Issue is milestoned to .NET 10 SR7 and labeled regressed-in-inflight/current
• No tests added; Gate result: ⚠️ SKIPPED (no tests detected)

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
PR	PR #34954	Null out pd.Handler before DismissViewController in DidFinishPicking	⚠️ SKIPPED (no tests in PR)	MediaPicker.ios.cs	Original PR

---

🔧 Fix — Analysis & Comparison

---

Fix Candidates

#	Source	Approach	Test Result	Files Changed	Notes
1	try-fix (opus-4.6)	Remove Handler?.Invoke() from PhotoPickerPresentationControllerDelegate.Dispose() entirely	⚠️ BLOCKED (compiles; no device)	MediaPicker.ios.cs	Relies solely on DidDismiss for swipe-cancel; may lose safety net
2	try-fix (sonnet-4.6)	Add _pickerCompleted flag + MarkCompleted() to delegate; gate Handler?.Invoke() in both DidDismiss and Dispose	⚠️ BLOCKED (compiles; no device)	MediaPicker.ios.cs	Explicit state; encapsulates cancel-vs-complete within delegate; more verbose
3	try-fix (gpt-5.3-codex)	Hold strong reference to PhotoPickerPresentationControllerDelegate on PhotoPickerDelegate to prevent premature GC	❌ FAIL (MSB3644 build env blocker)	MediaPicker.ios.cs	Prevents GC race by extending lifetime; build env blocked runtime test
4	try-fix (gpt-5.4)	Interlocked.Exchange atomic one-shot callback consumption	⚠️ BLOCKED (MSB3644 build env)	MediaPicker.ios.cs	Thread-safe but more complex than needed (iOS main-thread only)
PR	PR #34954	Null pd.Handler in DidFinishPicking before DismissViewController	⚠️ SKIPPED (Gate; no tests)	MediaPicker.ios.cs	Original PR; minimal, targeted, preserves cancel safety net

Cross-Pollination

Model	Round	New Ideas?	Details
claude-opus-4.6	2	No	NO NEW IDEAS — all approaches target same fundamental race

Exhausted: Yes (4/4 models, 1 cross-pollination round)
Selected Fix: PR's fix — null pd.Handler before DismissViewController — smallest, most targeted, preserves swipe-cancel safety net, no additional complexity

---

📋 Report — Final Recommendation

---

✅ Final Recommendation: APPROVE

Phase Status

Phase	Status	Notes
Pre-Flight	✅ COMPLETE	Issue #34953 — iOS regression in PickPhotosAsync for HEIC images
Gate	⚠️ SKIPPED	No tests in PR — recommend author adds tests
Try-Fix	✅ COMPLETE	4 attempts, 0 PASS (all BLOCKED by env / no iOS device); PR's fix selected as best
Report	✅ COMPLETE

Summary

PR #34954 fixes a GC race condition in MediaPicker.ios.cs that causes HEIC images picked via PickPhotosAsync to return blank. The fix is minimal, correctly targeted, and well-commented. All 4 alternative approaches explored via try-fix were either more complex or equivalent — none outperformed the PR's one-liner. Gate was SKIPPED because no tests were added; recommending tests via write-tests-agent.

Root Cause

PhotoPickerPresentationControllerDelegate.Dispose() invokes Handler?.Invoke() → tcs.TrySetResult([]) (empty list). This fires during GC after DismissViewController is called but before the async CompletedHandler finishes HEIC transcoding via NSItemProvider.LoadDataRepresentationAsync. HEIC is particularly vulnerable because transcoding is significantly slower than JPEG/PNG, widening the GC collection window.

Regression introduced by PR #34250 which moved CompletedHandler invocation into the DismissViewController completion callback.

Fix Quality

The fix is correct and minimal:

• Nulls pd.Handler in DidFinishPicking before DismissViewController — prevents the race at the exact right moment
• Preserves the swipe-cancel behavior: DidDismiss still fires Handler when user swipes down (the _pickerCompleted path is unaffected)
• Well-commented explaining the race condition

Minor observation (non-blocking): The single-photo PickPhotoAsync path (line ~133–162) has the same PhotoPickerPresentationControllerDelegate pattern. However, its CompletedHandler calls GetFileResult (synchronous), so the race window is much smaller. Out of scope for this PR.

Missing tests: Gate flagged no tests added. A device test verifying HEIC photo pick results is recommended.

---