fix(android): embedded surface renders with zero height on RN 0.85

packages/react-native-sandbox/android/src/main/java/io/callstack/rnsandbox/SandboxReactNativeView.kt

@@ -78,7 +78,21 @@ class SandboxReactNativeView(
         val w = right - left
         val h = bottom - top
         for (i in 0 until childCount) {
-            getChildAt(i).layout(0, 0, w, h)
+            val child = getChildAt(i)
+            // The child is a ReactSurfaceView from a SEPARATE ReactHost. Fabric
+            // lays our view out by calling layout() directly, without a measure
+            // pass, so the child never receives onMeasure(). But ReactSurfaceView
+            // only pushes layout constraints to its surface from onMeasure() (and
+            // its onLayout() is a no-op until wasMeasured is true). Without an
+            // explicit measure the nested surface keeps its initial constructor
+            // constraints and renders blank (regression surfaced on RN 0.85).
+            // Measure with EXACTLY specs so updateLayoutSpecs() runs with our real
+            // size, then lay the child out to fill us.
+            child.measure(
+                MeasureSpec.makeMeasureSpec(w, MeasureSpec.EXACTLY),
+                MeasureSpec.makeMeasureSpec(h, MeasureSpec.EXACTLY),
+            )
+            child.layout(0, 0, w, h)
         }
     }
 

packages/react-native-sandbox/src/index.tsx

@@ -7,7 +7,7 @@ import {
   useRef,
 } from 'react'
 import type {NativeSyntheticEvent} from 'react-native'
-import {StyleProp, StyleSheet, View, ViewProps, ViewStyle} from 'react-native'
+import {StyleProp, View, ViewProps, ViewStyle} from 'react-native'
 
 import type {NativeSandboxReactNativeViewComponentType} from '../specs/NativeSandboxReactNativeView'
 import NativeSandboxReactNativeView, {
@@ -305,9 +305,14 @@ const SandboxReactNativeView = forwardRef<
       return null
     }, [])
 
+    // The native sandbox view fills the user-styled wrapper as an in-flow
+    // flex child. It used to be position:absolute (StyleSheet.absoluteFillObject),
+    // but on RN 0.85 an absolutely-positioned child with all-zero insets no longer
+    // stretches to a flex-sized parent — it collapses to height 0 and the embedded
+    // surface renders blank. flex:1 makes it claim the wrapper's space reliably.
     const _style: StyleProp<ViewStyle> = useMemo(
       () => ({
-        ...StyleSheet.absoluteFillObject,
+        flex: 1,
       }),
       []
     )