[iOS] Fix: invoke MediaPicker completion handler after DismissViewController

[yuriikyry4enko]

Description of Change

On iOS, CompletedHandler was being invoked before DismissViewController
had finished animating. This means any code running in the handler — such as
showing an alert, opening a modal, or triggering navigation — would fire while
the picker view controller was still visible and attached to the view hierarchy.

iOS UIKit requires the presenting view controller to be fully visible and
attached before presenting any new UI (alerts, modals, sheets). If you attempt
to present something while a dismiss animation is still in progress, UIKit
silently drops the presentation or throws a warning, resulting in:

• DisplayAlert / DisplayActionSheet not appearing after picking an image
• Custom modal dialogs not showing up
• Any await-based UI call after PickPhotoAsync / PickVideoAsync silently failing on iOS, while working fine on Android

The root cause is that DismissViewController(animated:completion:) accepts a
completion callback precisely for this purpose — to run logic after the
animation finishes — but the original code passed null and called the handler
immediately after, creating a race condition.

Fix: Moved all CompletedHandler invocations into the completion callback
of DismissViewController across three call sites:

• UIImagePickerControllerDelegate.FinishedPickingMedia
• UIImagePickerControllerDelegate.Canceled
• PHPickerViewControllerDelegate.DidFinishPicking

Issues Fixed

Fixes #21996

Testing

Tested on a physical iOS device.

• Opened image picker via MediaPicker.PickPhotoAsync()
• After selecting an image, called DisplayAlert in the continuation
• Before fix: alert did not appear after dismissing the picker
• After fix: alert appears correctly after the picker is fully dismissed

[dotnet-policy-service]

Hey there @@yuriikyry4enko! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jfversluis]

@yuriikyry4enko thanks for this! Are you sure this isn't already working for .NET 10? Because a lot changed for the MediaPicker in .NET 10.

[yuriikyry4enko]

@yuriikyry4enko thanks for this! Are you sure this isn't already working for .NET 10? Because a lot changed for the MediaPicker in .NET 10.

I was able to reproduce the issue on a physical device — tested on iPhone 16, iOS 26.2.1. Attaching a sample project for reference.

MediaPickerExample.zip

[jfversluis]

Multi-Model Code Review — PR #34250

Reviewed by 3 independent AI models (Claude Sonnet 4.5, GPT-5.2, Gemini 3 Pro) via Copilot CLI

Is this still needed?

YES. The file MediaPicker.ios.cs has identical SHA on both main and net10.0 branches. The bug is not fixed anywhere.

Is the fix correct?

All 3 models agree: YES, the core approach is correct. Moving CompletedHandler into the DismissViewController completion callback is the textbook iOS UIKit pattern — it ensures the picker is fully dismissed before resolving the TaskCompletionSource, which prevents subsequent UI presentations (like DisplayAlert) from silently failing.

The PHPickerViewController path (iOS 14+, most common) is clean and correct as-is.

---

Issues Found (consensus across all 3 models)

1. 🚨 Double-dismiss on UIImagePickerController path

All 3 models independently flagged this. After this PR, the sequence is:

1. FinishedPickingMedia calls DismissViewController(true, () => CompletedHandler?.Invoke(info))
2. Dismiss completes → CompletedHandler runs
3. CompletedHandler calls await picker.DismissViewControllerAsync(true) — second dismiss on already-dismissed VC

The CompletedHandler lambda (~line 140-144) still contains its own dismiss call:

CompletedHandler = async info =>
{
    GetFileResult(info, tcs, options);
    await picker.DismissViewControllerAsync(true); // ← redundant, VC already dismissed by delegate
}

Risk: Low (UIKit typically no-ops on already-dismissed VCs), but it's a code smell that could produce console warnings. Recommendation: Remove await picker.DismissViewControllerAsync(true) from the CompletedHandler since the delegate now handles dismissal.

2. ⚠️ Whitespace inconsistency (tabs vs spaces)

The FinishedPickingMedia method changed from tab indentation to space indentation, and DidFinishPicking has mixed tabs/spaces. Please run dotnet format or manually align to match the existing file style before merge.

---

Things That Look Good

• ✅ The var captured pattern in DidFinishPicking is good defensive coding — captures and sanitizes results before the async callback
• ✅ No threading concerns — all paths run on the main thread via UIKit completion callbacks
• ✅ tcs.TrySetResult is thread-safe
• ✅ The slight delay from waiting for dismiss animation (~400ms) is actually desirable — it's what prevents the race condition

Summary

The fix is the right approach and resolves the core issue. Please address:

1. Remove the redundant dismiss in the UIImagePickerController CompletedHandler (~line 143)
2. Fix whitespace to match existing file style

After those changes, this is good to merge. 👍

[yuriikyry4enko]

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[jfversluis]

Thanks for addressing the double-dismiss issue! 👍

One remaining thing: the lambda at line ~140 still has async but no longer contains any await:

CompletedHandler = async info =>
{
    GetFileResult(info, tcs, options);
}

This will trigger compiler warning CS1998 ("This async method lacks 'await' operators and will run synchronously"). Since the await picker.DismissViewControllerAsync(true) was removed, the async keyword should be removed too:

CompletedHandler = info =>
{
    GetFileResult(info, tcs, options);
}

[jfversluis]

/azp run maui-pr

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

The base branch was changed.

[github-actions]

🚀 Dogfood this PR with:

⚠️ WARNING: Do not do this without first carefully reviewing the code of this PR to satisfy yourself it is safe.

curl -fsSL https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.sh | bash -s -- 34250

Or

• Run remotely in PowerShell:

iex "& { $(irm https://raw.githubusercontent.com/dotnet/maui/main/eng/scripts/get-maui-pr.ps1) } 34250"