[iOS 26] Sheet scaled to ~96% width at non-large detents (8pt side margins) despite presentation="page"; dimming also broken

[kinghennry]

Description

On iOS 26, UISheetPresentationController applies a scale(0.961) transform to UIDropShadowView (the sheet's presentation wrapper) at every non-large detent. This shrinks the sheet from the full screen width to ~96%, centered — leaving ~8pt margins on both sides (the new "floating sheet" look).

This happens even with presentation="page" (i.e. prefersPageSizing = YES), which should render a bottom-attached, full-width page sheet. At the large detent the transform is identity and the sheet is correctly full-width — which is why dragging a sheet up appears to "fix" it.

It affects every sheet. It's usually invisible (a dark sheet over a dark screen), but over full-bleed media (a photo/video filling the screen) those 8pt margins expose the content behind the sheet and read as broken edges.

Environment

• @lodev09/react-native-true-sheet 3.11.6
• iOS 26.2 SDK, iPhone 11, portrait-locked (orientation: portrait)
• React Native 0.83 / Expo SDK 55, New Architecture (Fabric)

Reproduction

1. Render a full-bleed image/video that fills the screen.
2. Present a TrueSheet over it at a non-large detent — e.g. detents={['auto']} or detents={[0.7, 0.95]} — with the default presentation="page".
3. The sheet shows ~8pt of the media on each side.
4. Drag it to the large detent → it snaps to full width and the margins disappear.

Measured

Native RCTLogWarn dump of the presentation hierarchy at present-time (screen is 414 x 896):

feed-options (auto, bad):  UIDropShadowView f={{8,488},{398,400}} b={{0,0},{414,416}} tf=[0.961 0 0 0.961 0 0]
comments @0.7   (bad):     UIDropShadowView f={{8,252},{398,635}} b={{0,0},{414,661}} tf=[0.961 0 0 0.961 0 4.8]
comments @0.95  (OK):      UIDropShadowView f={{0,48},{414,848}}  b={{0,0},{414,848}} tf=[1.0   0 0 1.0   0 0]
plain screen    (bad):     UIDropShadowView f={{8,424},{398,464}} b={{0,0},{414,482}} tf=[0.961 0 0 0.961 0 1.3]

Note bounds is always full-width (414) — only the transform insets it. The last row is a sheet on a plain (non-media) screen: it has the identical 0.961 scale. The inset is always present; media only makes it visible.

Ruled out

• The sheet's own frame is full-width; verticalSizeClass = Regular (not compact)
• prefersPageSizing = 1, widthFollowsPreferredContentSizeWhenEdgeAttached = 0, preferredContentSize = {0,0} — all as TrueSheet sets them; iOS is not overriding them
• No layer mask, no cornerRadius/maskedCorners difference between the working and broken cases
• Setting prefersEdgeAttachedInCompactHeight = NO changes nothing (expected — the app is portrait-locked, so compact height never applies)
• Not media-specific (see the plain-screen row above)

Second bug (related)

UIDimmingView renders with a fully transparent background (backgroundColor alpha = 0) on iOS 26, so dimmed never actually dims the backdrop — even though largestUndimmedDetentIdentifier is correctly set to nil (with dimmed=true and dimmedDetentIndex=0, per TrueSheetViewController.mm).

This is what makes bug #1 visible in practice: with a working dim, the 8pt margins would read as dark rather than exposing bright content.

Note for anyone attempting a workaround

Forcing UIDropShadowView.transform = CGAffineTransformIdentity in viewDidLayoutSubviews does not work: iOS re-applies the scale on the next layout pass (causing flicker), and mutating the wrapper's frame desyncs it from the detent/drag model (a single-detent sheet becomes draggable).

Happy to test any patch or provide more native dumps.

[github-actions]

Hey @kinghennry! Thanks for opening the issue.

It looks like your issue is missing a valid reproduction link.

A minimal reproduction helps us investigate and fix the issue faster. Without one, we may not be able to help.

Please provide one of the following:

• A GitHub repository under your username
• An Expo Snack

See "How to create a Minimal, Reproducible Example" for more guidance.

You can edit your original issue or leave a comment with the repro link. Issues without reproductions may be closed after 14 days.

[kinghennry]

Reproduction: https://github.com/kinghennry/truesheet-ios26-repro

Requires an iOS 26 device/simulator + a dev build (TrueSheet is a native Fabric module, so it won't run in Expo Go):

npm install
npx expo run:ios

Steps

1. Tap Present sheet — it opens at the 0.5 detent.
2. Look at the sheet's left and right edges → ~8pt of the red background shows on each side.
3. Drag the sheet up to the 0.95 (large) detent → the red disappears and the sheet is full width.

The repro deliberately uses a plain bright red background rather than media: the scale(0.961) on UIDropShadowView is applied at every non-large detent regardless of what's behind the sheet — a bright backdrop just makes the margins visible. (In our app it first showed up as a full-bleed photo/video peeking through the sheet's edges, which made it look media-specific. It isn't.)

Happy to add more native dumps or test a patch.

[github-actions]

Thank you for providing a repro! We'll take a look at this issue soon.

[lodev09]

@kinghennry TrueSheet uses native IOS sheet presentation, it doesn't have control on the sheet layout itself. This is default in IOS 26. Closing