android: size custom top-bar component buttons to content via a single bounded measure (Fabric)#8328
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…ports its size On the New Architecture (Fabric), a custom React-component top bar button without explicit width/height could collapse to ~1px. The hosted React surface lays out asynchronously, off the native measure pass, so the first onMeasure often observes a 0-sized child and freezes the button at the ~1px floor with no subsequent re-measure. Attach an OnLayoutChangeListener to the hosted child that re-requests layout when the content's size changes (so onMeasure re-runs and sizes the button to the content). The size-changed guard makes it converge once the button matches the content. The explicit-dimensions check is done inside the listener because onViewAdded fires from the superclass constructor (before `component` is assigned) for the React surface view we need to observe. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The new test hardcoded the collapsed button width as 1px, which only holds at mdpi (density 1.0). CI runs at a higher density, where resolveFinalWidth(0) = ceil(dpToPx(1dp)) > 1. Derive the expected value from the same dpToPx formula the production code uses instead of hardcoding it. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The re-measure assertion failed (expected 25 but was 1) because View.measure() caches results: re-measuring the button with the same outer spec reused the child's stale cached 0-width measurement, so resolveFinalWidth still saw 0. In production RN re-measures the surface when it lays out new content; model that with child.forceLayout() (after child.layout(), which clears FORCE_LAYOUT) so the parent's super.onMeasure observes the real content width. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
…e bounded measure Custom React-component top bar buttons without explicit width/height collapsed to ~1px (invisible) under the New Architecture (Fabric). The two-pass measurement from #8320/#8326 re-measured the hosted ReactSurfaceView with an EXACTLY box derived from the first (often still-empty) discovery pass; that forced box is pushed to Fabric via updateLayoutSpecs, so Fabric keeps laying the content out into the collapsed box and the button never recovers. The same forcing also stretched flex-content buttons to the full bar height. Replace the two-pass with a single bounded (AT_MOST) measure and let ReactSurfaceView size itself to its content (its documented AT_MOST max-of-children behavior). When Fabric mounts/sizes the content it re-requests layout and this measure runs again against the real content size. Explicit width/height still measure EXACTLY; vertical centering is preserved by the existing CENTER_VERTICAL gravity. Verified on-device (Pixel 7, newArch+Hermes) on RN 0.78.3 and 0.85.2: content-hugging and flex component buttons render correctly; flex buttons are pixel-identical to before. Unit tests updated for the single-pass contract. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
israelko
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Ligamer24
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Jun 11, 2026
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Summary
topBar.leftButtons/rightButtonswith{ component }) collapsing to ~1px (invisible) on Android under the New Architecture (Fabric) when they don't declare explicitwidth/height. A content-hugging button (e.g.<View><Text/></View>) disappears entirely; when it's a left button it also takes the back-button slot, so the back affordance appears to vanish too.ReactSurfaceViewwith anEXACTLYbox derived from the first (often still-empty) discovery pass. That forced box is pushed to Fabric viaupdateLayoutSpecs, so Fabric keeps laying the content out into the collapsed box and the button never recovers. The same forcing also stretched flex-content buttons to the full bar height.AT_MOST) measure and letReactSurfaceViewsize itself to its content (its documentedAT_MOST= max-of-children behavior). When Fabric mounts/sizes the content it re-requests layout andonMeasureruns again against the real size. Explicitwidth/heightstill measureEXACTLY; vertical centering is preserved by the existingCENTER_VERTICALgravity. Net change is a simplification (−108 / +26).Validation
TitleBarReactButtonViewTestupdated for the single-pass contract — 6/6 pass, including the centering test.newArchEnabled+hermesEnabled), RN 0.78.3 and 0.85.2:RoundedButton): renders correctly, pixel-identical to before this change.