[ScrollView][iOS] Refactor ScrollView inset handling to lay out natively

packages/react-native/Libraries/Components/ScrollView/ScrollView.js

@@ -16,16 +16,13 @@ import type {ColorValue} from '../../StyleSheet/StyleSheet';
 import type {
   GestureResponderEvent,
   LayoutChangeEvent,
-  SafeAreaInsets,
-  SafeAreaInsetsChangeEvent,
   ScrollEvent,
 } from '../../Types/CoreEventTypes';
 import type {EventSubscription} from '../../vendor/emitter/EventEmitter';
 import type {KeyboardEvent, KeyboardMetrics} from '../Keyboard/Keyboard';
 import type {ViewProps} from '../View/ViewPropTypes';
 import type {ScrollViewStickyHeaderProps} from './ScrollViewStickyHeader';
 
-import getSafeAreaContentPadding from '../../../src/private/components/scrollview/getSafeAreaContentPadding';
 import {
   HScrollContentViewNativeComponent,
   HScrollViewNativeComponent,
@@ -891,11 +888,6 @@ class ScrollView extends React.Component<ScrollViewProps, ScrollViewState> {
     layoutHeight: null,
   };
 
-  // The latest safe area insets of the native view. Only the pair across the
-  // scrollable axis affects the content container, so a change to the other
-  // pair is kept here without a render.
-  _safeAreaInsets: ?SafeAreaInsets = null;
-
   componentDidMount() {
     this._keyboardMetrics = Keyboard.metrics();
     this._additionalScrollOffset = 0;
@@ -1260,30 +1252,6 @@ class ScrollView extends React.Component<ScrollViewProps, ScrollViewState> {
     this.props.onScroll && this.props.onScroll(e);
   };
 
-  _handleSafeAreaInsetsChange = (e: SafeAreaInsetsChangeEvent) => {
-    const {insets} = e.nativeEvent;
-    const previous = this._safeAreaInsets;
-    this._safeAreaInsets = insets;
-    const changedAcrossScrollableAxis =
-      previous == null ||
-      (this.props.horizontal === true
-        ? previous.top !== insets.top || previous.bottom !== insets.bottom
-        : previous.left !== insets.left || previous.right !== insets.right);
-    if (changedAcrossScrollableAxis && this._padsContentForSafeArea()) {
-      this.forceUpdate();
-    }
-    this.props.experimental_onSafeAreaInsetsChange?.(e);
-  };
-
-  /**
-   * Whether the content container is padded by the safe area across the
-   * scrollable axis.
-   */
-  _padsContentForSafeArea(): boolean {
-    const behavior = this.props.contentInsetAdjustmentBehavior;
-    return Platform.OS === 'ios' && behavior != null && behavior !== 'never';
-  }
-
   _handleLayout = (e: LayoutChangeEvent) => {
     if (this.props.invertStickyHeaders === true) {
       this.setState({layoutHeight: e.nativeEvent.layout.height});
@@ -1784,25 +1752,9 @@ class ScrollView extends React.Component<ScrollViewProps, ScrollViewState> {
       ? HScrollContentViewNativeComponent
       : VScrollContentViewNativeComponent;
 
-    // Along the scrollable axis UIKit turns the safe area into content insets,
-    // so content scrolls under the system UI. Across it there is nothing to
-    // scroll, so the content container is padded instead and content is laid
-    // out clear of the system UI, such as the rail on iPhone Duo. Native
-    // removes whatever UIKit insets across that axis, so the safe area applies
-    // once.
-    const padsContentForSafeArea = this._padsContentForSafeArea();
-    const safeAreaInsets = this._safeAreaInsets;
-
     const contentContainerStyle = [
       horizontal && styles.contentContainerHorizontal,
       this.props.contentContainerStyle,
-      padsContentForSafeArea && safeAreaInsets != null
-        ? getSafeAreaContentPadding(
-            this.props.contentContainerStyle,
-            safeAreaInsets,
-            horizontal,
-          )
-        : null,
     ];
     if (__DEV__ && this.props.style !== undefined) {
       // $FlowFixMe[underconstrained-implicit-instantiation]
@@ -1939,14 +1891,6 @@ class ScrollView extends React.Component<ScrollViewProps, ScrollViewState> {
       onTouchStart: this._handleTouchStart,
       onTouchCancel: this._handleTouchCancel,
       onScroll: this._handleScroll,
-      // Routed through the handler whenever the event is observed at all, so
-      // the insets it keeps are current when the behavior changes from
-      // 'never' and the content container starts padding for them.
-      experimental_onSafeAreaInsetsChange:
-        padsContentForSafeArea ||
-        this.props.experimental_onSafeAreaInsetsChange != null
-          ? this._handleSafeAreaInsetsChange
-          : undefined,
       endDraggingSensitivityMultiplier:
         experimental_endDraggingSensitivityMultiplier,
       scrollEventThrottle: hasStickyHeaders

packages/react-native/React/Fabric/Mounting/ComponentViews/RCTFabricComponentsPlugins.h

@@ -35,6 +35,7 @@ Class<RCTComponentViewProtocol> RCTInputAccessoryCls(void) __attribute__((used))
 Class<RCTComponentViewProtocol> RCTParagraphCls(void) __attribute__((used));
 Class<RCTComponentViewProtocol> RCTPullToRefreshViewCls(void) __attribute__((used));
 Class<RCTComponentViewProtocol> RCTSafeAreaViewCls(void) __attribute__((used));
+Class<RCTComponentViewProtocol> RCTScrollContentViewCls(void) __attribute__((used));
 Class<RCTComponentViewProtocol> RCTScrollViewCls(void) __attribute__((used));
 Class<RCTComponentViewProtocol> RCTSwitchCls(void) __attribute__((used));
 Class<RCTComponentViewProtocol> RCTTextInputCls(void) __attribute__((used));

packages/react-native/React/Fabric/Mounting/ComponentViews/RCTFabricComponentsPlugins.mm

@@ -24,6 +24,7 @@
     {"Paragraph", RCTParagraphCls},
     {"PullToRefreshView", RCTPullToRefreshViewCls},
     {"SafeAreaView", RCTSafeAreaViewCls},
+    {"ScrollContentView", RCTScrollContentViewCls},
     {"ScrollView", RCTScrollViewCls},
     {"Switch", RCTSwitchCls},
     {"TextInput", RCTTextInputCls},

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollContentViewComponentView.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import <UIKit/UIKit.h>
+
+#import <React/RCTViewComponentView.h>
+
+NS_ASSUME_NONNULL_BEGIN
+
+/*
+ * UIView class for the <ScrollContentView> component, the content container of a <ScrollView>.
+ */
+@interface RCTScrollContentViewComponentView : RCTViewComponentView
+
+/*
+ * The safe area the content is laid out clear of, as padding on top of the content container's own. The enclosing
+ * scroll view sets the pair of insets across its scrollable axis, and zero while its `contentInsetAdjustmentBehavior`
+ * is `never`.
+ */
+@property (nonatomic, assign) UIEdgeInsets safeAreaPadding;
+
+@end
+
+NS_ASSUME_NONNULL_END

packages/react-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollContentViewComponentView.mm

@@ -0,0 +1,106 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTScrollContentViewComponentView.h"
+
+#import <React/RCTI18nUtil.h>
+#import <React/RCTUtils.h>
+#import <react/renderer/components/scrollview/ScrollContentViewComponentDescriptor.h>
+#import <react/renderer/components/scrollview/ScrollContentViewState.h>
+#import "RCTConversions.h"
+#import "RCTFabricComponentsPlugins.h"
+
+using namespace facebook::react;
+
+@implementation RCTScrollContentViewComponentView {
+  ScrollContentViewShadowNode::ConcreteState::Shared _state;
+}
+
+- (instancetype)initWithFrame:(CGRect)frame
+{
+  if (self = [super initWithFrame:frame]) {
+    _props = ScrollContentViewShadowNode::defaultSharedProps();
+  }
+
+  return self;
+}
+
+- (void)setSafeAreaPadding:(UIEdgeInsets)safeAreaPadding
+{
+  _safeAreaPadding = safeAreaPadding;
+  [self _updateStateIfNecessary];
+}
+
+- (void)_updateStateIfNecessary
+{
+  if (!_state) {
+    return;
+  }
+
+  UIEdgeInsets insets = _safeAreaPadding;
+  insets.left = RCTRoundPixelValue(insets.left);
+  insets.top = RCTRoundPixelValue(insets.top);
+  insets.right = RCTRoundPixelValue(insets.right);
+  insets.bottom = RCTRoundPixelValue(insets.bottom);
+
+  auto newPadding = RCTEdgeInsetsFromUIEdgeInsets(insets);
+  RCTI18nUtil *i18nUtil = [RCTI18nUtil sharedInstance];
+  auto layoutDirection = i18nUtil.isRTL ? LayoutDirection::RightToLeft : LayoutDirection::LeftToRight;
+  bool swapLeftAndRightInRTL = i18nUtil.isRTL && i18nUtil.doLeftAndRightSwapInRTL;
+  auto threshold = 1.0 / RCTScreenScale() + 0.01; // Size of a pixel plus some small threshold.
+
+  _state->updateState(
+      [=](const ScrollContentViewShadowNode::ConcreteState::Data &oldData)
+          -> ScrollContentViewShadowNode::ConcreteState::SharedData {
+        auto deltaPadding = newPadding - oldData.safeAreaPadding;
+
+        if (std::abs(deltaPadding.left) < threshold && std::abs(deltaPadding.top) < threshold &&
+            std::abs(deltaPadding.right) < threshold && std::abs(deltaPadding.bottom) < threshold &&
+            oldData.layoutDirection == layoutDirection && oldData.swapLeftAndRightInRTL == swapLeftAndRightInRTL) {
+          return nullptr;
+        }
+
+        auto newData = oldData;
+        newData.safeAreaPadding = newPadding;
+        newData.layoutDirection = layoutDirection;
+        newData.swapLeftAndRightInRTL = swapLeftAndRightInRTL;
+        return std::make_shared<const ScrollContentViewShadowNode::ConcreteState::Data>(newData);
+      });
+}
+
+#pragma mark - RCTComponentViewProtocol
+
++ (ComponentDescriptorProvider)componentDescriptorProvider
+{
+  return concreteComponentDescriptorProvider<ScrollContentViewComponentDescriptor>();
+}
+
+- (void)updateState:(const facebook::react::State::Shared &)state
+           oldState:(const facebook::react::State::Shared &)oldState
+{
+  _state = std::static_pointer_cast<const ScrollContentViewShadowNode::ConcreteState>(state);
+}
+
+- (void)finalizeUpdates:(RNComponentViewUpdateMask)updateMask
+{
+  [super finalizeUpdates:updateMask];
+  [self _updateStateIfNecessary];
+}
+
+- (void)prepareForRecycle
+{
+  [super prepareForRecycle];
+  _state.reset();
+  _safeAreaPadding = UIEdgeInsetsZero;
+}
+
+@end
+
+Class<RCTComponentViewProtocol> RCTScrollContentViewCls(void)
+{
+  return RCTScrollContentViewComponentView.class;
+}