feat(iOS, FormSheet v5): Add support for preventNativeDismiss & onNativeDismissPrevented

[t0maboro]

Description

Adds preventNativeDismiss support. When preventNativeDismiss is true, the user cannot dismiss the sheet natively via swipe-down or by tapping the backdrop. Programmatic dismissal from JS still works.
When dismissal is prevented, the sheet emits a new onNativeDismissPrevented event so JS can react.

Note

Backdrop taps need extra handling because UIKit doesn't fire delegate callbacks for this path. I follow the same approach as in #3771 with attaching a UITapGestureRecognizer to the presentation controller's containerView and filter touches, so only taps outside presentedView are recognized. The recognizer is attached/detached in viewWillAppear/viewDidDisappear, because UIKit recreates the container view on every present cycle.

Closes: https://github.com/software-mansion/react-native-screens-labs/issues/1272

Changes

• preventNativeDismiss prop
• onNativeDismissPrevented event
• attached a UITapGestureRecognizer for backdrop taps.
• overriden delegate methods: presentationControllerShouldDismiss , presentationControllerDidAttemptToDismiss

Visual documentation

preventnativedismiss.mov

[Copilot]

Pull request overview

This PR extends the experimental Gamma FormSheet (Fabric/iOS) implementation with a preventNativeDismiss prop to block user-initiated dismiss (swipe-down + backdrop tap), and introduces an onNativeDismissPrevented event so JS can react to blocked dismissal attempts.

Changes:

• Added preventNativeDismiss to the FormSheet JS API and Fabric native component props.
• Added onNativeDismissPrevented event plumbing (codegen prop → C++ event emitter → ObjC++ event emitter → JS).
• Implemented iOS native prevention via UIAdaptivePresentationControllerDelegate and a custom backdrop UITapGestureRecognizer, plus added an SFT scenario for manual validation.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/fabric/gamma/modals/form-sheet/FormSheetHostNativeComponent.ts	Adds codegen prop/event definitions for preventNativeDismiss + onNativeDismissPrevented.
src/components/gamma/modals/form-sheet/FormSheet.types.ts	Exposes the new prop + event in the public TS types/docs.
ios/gamma/modals/form-sheet/RNSFormSheetHostEventEmitter.mm	Emits onNativeDismissPrevented to JS when dismissal is blocked.
ios/gamma/modals/form-sheet/RNSFormSheetHostEventEmitter.h	Declares emitOnNativeDismissPrevented.
ios/gamma/modals/form-sheet/RNSFormSheetHostComponentView.mm	Tracks preventNativeDismiss prop and forwards it to the controller; emits prevented event via delegate callback.
ios/gamma/modals/form-sheet/RNSFormSheetContentController.mm	Implements presentationControllerShouldDismiss / ...DidAttemptToDismiss and backdrop-tap interception via gesture recognizer.
ios/gamma/modals/form-sheet/RNSFormSheetContentController.h	Adds delegate method + preventNativeDismiss property.
apps/src/tests/single-feature-tests/form-sheet/test-form-sheet-prevent-native-dismiss-ios/scenario.md	Adds manual test scenario documentation for the new behavior.
apps/src/tests/single-feature-tests/form-sheet/test-form-sheet-prevent-native-dismiss-ios/index.tsx	Adds an SFT screen to exercise the new prop/event.
apps/src/tests/single-feature-tests/form-sheet/index.ts	Registers the new SFT scenario in the FormSheet group.

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[kligarski]

Screen.Recording.2026-05-18.at.17.53.06.mov

might be related to missing detachBackdropTapGestureRecognizer call

[kligarski]

This isn't used right now - should it be?

[t0maboro]

4124bf3

[LKuchno]

Looks good, thank you!