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.

Important

I know that this implementation is messy, so we may wait before landing this PR to proceed with the refactor we discussed internally, or merge it and the adapt together with other props.

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]

Suggested change

	* The default value is `false`.
	*
	*
	* @default false

[kligarski]

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

[LKuchno]

I'm not sure why this information is placed in scenario. It's a bit misleading, taking into consideration the fact that this option is already enabled when we open the screen (which is the expected state). Could you explain why we need it here?

[LKuchno]

Could we capitalize the scenario name to PreventNativeDismiss so that it's consistent with both the other scenarios and its own scenarioDescription name?