🐛 End the wait when a document picker sheet is swiped away

[anggrayudi]

Closes #138. Follows up on my comment there.

The gap

PHPickerViewController gets a UIAdaptivePresentationControllerDelegate so a swipe dismissal resumes the caller. The two UIDocumentPickerViewController paths never got one:

Line	Picker	.delegate	presentationController.delegate
222	UIDocumentPickerViewController (save)	✅	❌ → now ✅
312	UIImagePickerController (camera)	✅	❌ (untouched)
557	UIDocumentPickerViewController (open)	✅	❌ → now ✅
614–615	PHPickerViewController	✅	✅

So when documentPickerWasCancelled does not fire — which @derynia reports happens when the swipe starts before the presentation animation finishes — the suspendCancellableCoroutine waits forever and the tap looks dead.

The change

Rather than a second delegate object mirroring PhPickerDismissDelegate, DocumentPickerDelegate now implements both protocols behind one finishOnce() guard.

That is deliberate. A dismissal frequently reports through both documentPickerWasCancelled and presentationControllerDidDismiss, and the call sites resume a continuation that accepts exactly one answer — a second resume throws IllegalStateException. One object with one guard makes double-resume impossible. (For what it's worth, the PHPicker pair has its guard only on PhPickerDelegate, not on PhPickerDismissDelegate.)

presentationController?.delegate = … is a no-op where there is no presentation controller, so styles without one behave exactly as before.

The camera path is left alone — it is full-screen and not what #138 describes.

Verification, and its limits

Tested: three new tests in filekit-dialogs/src/iosTest covering the delegate contract — swipe-dismiss with no cancel callback reports cancelled; cancel followed by swipe-dismiss reports cancelled once; a pick followed by swipe-dismiss reports only the pick. 45 tests pass on iosSimulatorArm64Test, compileKotlinIosArm64 clean. Disabling finishOnce() makes two of the three fail, so the guard is doing real work.

Not tested — please read before merging: I could not reproduce the original bug or observe the fix working on a simulator. Driving a mid-animation swipe needs synthetic UI events, and the environment I work in cannot grant the Accessibility permission that requires; two attempts got as far as a running sample app and no further. So this fix is argued from the delegate contract, the pattern already in this repo, and the reporter's description — not from watching the symptom disappear.

You said in October 2024 that you could reproduce it. If you can run that same reproduction against this branch, that is the check I was unable to do.

Why it may matter more than a missing callback

Field report, cause unconfirmed: in an app I work on the iOS file picker intermittently stopped opening at all, and stayed broken until the app was killed. UIKit ignores presentViewController() while the presenter already has a presentedViewController, and that presenter is the root view controller — so one picker left presented breaks every later one. We patched the symptom by clearing stale presentations before launching, and never identified the trigger. If a mid-animation swipe can leave the controller presented while no delegate fires, this issue would explain it. I cannot prove that link.

🤖 Generated with Claude Code

[vinceglb]

Hi @anggrayudi, thanks for the focused change and for documenting the verification limits.

The shared completion guard makes sense: adding a second cancellation callback requires preventing duplicate continuation resumes, and keeping both protocols on the same delegate is a straightforward solution.

I can't approve this as a fix for #138 yet. The original report also affects the photo/video picker, which already uses presentationControllerDidDismiss through PhPickerDismissDelegate. Adding the same callback to the document picker is reasonable, but does not establish that UIKit delivers it during the problematic early swipe. The new tests verify callback handling once that callback is invoked; they do not exercise that missing piece.

Before merging, please provide a before/after reproduction: swipe the document picker away before its opening animation finishes, confirm the suspended call completes exactly once with this patch, and confirm another picker can open afterward. Please include the iOS version and check ordinary cancellation and file selection too.

Please also replace Closes #138 with Related to #138 unless the photo/video case is verified as resolved. The comment above presentationControllerDidDismiss should describe this as a fallback rather than asserting that it fixes the early-animation case until that is demonstrated.

The implementation looks maintainable; the remaining concern is proving the behavior it claims to fix.