Add fabric support for maintainVisibleContentPosition on iOS

React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm

@@ -22,6 +22,7 @@
 #import "RCTConversions.h"
 #import "RCTEnhancedScrollView.h"
 #import "RCTFabricComponentsPlugins.h"
+#import "RCTPullToRefreshViewComponentView.h"
 
 using namespace facebook::react;
 
@@ -99,6 +100,11 @@ @implementation RCTScrollViewComponentView {
  BOOL _shouldUpdateContentInsetAdjustmentBehavior;
 
  CGPoint _contentOffsetWhenClipped;
+
+ __weak UIView *_contentView;
+
+ CGRect _prevFirstVisibleFrame;
+ __weak UIView *_firstVisibleView;
 }
 
 + (RCTScrollViewComponentView *_Nullable)findScrollViewComponentViewForView:(UIView *)view
@@ -148,10 +154,17 @@ - (void)dealloc
 
 #pragma mark - RCTMountingTransactionObserving
 
+- (void)mountingTransactionWillMount:(const facebook::react::MountingTransaction &)transaction
+ withSurfaceTelemetry:(const facebook::react::SurfaceTelemetry &)surfaceTelemetry
+{
+ [self _prepareForMaintainVisibleScrollPosition];
+}
+
 - (void)mountingTransactionDidMount:(MountingTransaction const &)transaction
  withSurfaceTelemetry:(facebook::react::SurfaceTelemetry const &)surfaceTelemetry
 {
  [self _remountChildren];
+ [self _adjustForMaintainVisibleContentPosition];
 }
 
 #pragma mark - RCTComponentViewProtocol
@@ -336,11 +349,23 @@ - (void)_preserveContentOffsetIfNeededWithBlock:(void (^)())block
 - (void)mountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
 {
  [_containerView insertSubview:childComponentView atIndex:index];
+ if ([childComponentView isKindOfClass:RCTPullToRefreshViewComponentView.class]) {
+ // Ignore the pull to refresh component.
+ } else {
+ RCTAssert(_contentView == nil, @"RCTScrollView may only contain a single subview.");
+ _contentView = childComponentView;
+ }
 }
 
 - (void)unmountChildComponentView:(UIView<RCTComponentViewProtocol> *)childComponentView index:(NSInteger)index
 {
  [childComponentView removeFromSuperview];
+ if ([childComponentView isKindOfClass:RCTPullToRefreshViewComponentView.class]) {
+ // Ignore the pull to refresh component.
+ } else {
+ RCTAssert(_contentView == childComponentView, @"Attempted to remove non-existent subview");
+ _contentView = nil;
+ }
 }
 
 /*
@@ -403,6 +428,9 @@ - (void)prepareForRecycle
  CGRect oldFrame = self.frame;
  self.frame = CGRectZero;
  self.frame = oldFrame;
+ _contentView = nil;
+ _prevFirstVisibleFrame = CGRectZero;
+ _firstVisibleView = nil;
  [super prepareForRecycle];
 }
 
@@ -683,6 +711,74 @@ - (void)removeScrollListener:(NSObject<UIScrollViewDelegate> *)scrollListener
  [self.scrollViewDelegateSplitter removeDelegate:scrollListener];
 }
 
+#pragma mark - Maintain visible content position
+
+- (void)_prepareForMaintainVisibleScrollPosition
+{
+ const auto &props = *std::static_pointer_cast<const ScrollViewProps>(_props);
+ if (!props.maintainVisibleContentPosition) {
+ return;
+ }
+
+ BOOL horizontal = _scrollView.contentSize.width > self.frame.size.width;
+ int minIdx = props.maintainVisibleContentPosition.value().minIndexForVisible;
+ for (NSUInteger ii = minIdx; ii < _contentView.subviews.count; ++ii) {
+ // Find the first entirely visible view.
+ UIView *subview = _contentView.subviews[ii];
+ BOOL hasNewView = NO;
+ if (horizontal) {
+ hasNewView = subview.frame.origin.x > _scrollView.contentOffset.x;
+ } else {
+ hasNewView = subview.frame.origin.y > _scrollView.contentOffset.y;
+ }
+ if (hasNewView || ii == _contentView.subviews.count - 1) {
+ _prevFirstVisibleFrame = subview.frame;
+ _firstVisibleView = subview;
+ break;
+ }
+ }
+}
+
+- (void)_adjustForMaintainVisibleContentPosition
+{
+ const auto &props = *std::static_pointer_cast<const ScrollViewProps>(_props);
+ if (!props.maintainVisibleContentPosition) {
+ return;
+ }
+
+ std::optional<int> autoscrollThreshold = props.maintainVisibleContentPosition.value().autoscrollToTopThreshold;
+ BOOL horizontal = _scrollView.contentSize.width > self.frame.size.width;
+ // TODO: detect and handle/ignore re-ordering
+ if (horizontal) {
+ CGFloat deltaX = _firstVisibleView.frame.origin.x - _prevFirstVisibleFrame.origin.x;
+ if (ABS(deltaX) > 0.5) {
+ CGFloat x = _scrollView.contentOffset.x;
+ [self _forceDispatchNextScrollEvent];
+ _scrollView.contentOffset = CGPointMake(_scrollView.contentOffset.x + deltaX, _scrollView.contentOffset.y);
+ if (autoscrollThreshold) {
+ // If the offset WAS within the threshold of the start, animate to the start.
+ if (x <= autoscrollThreshold.value()) {
+ [self scrollToOffset:CGPointMake(0, _scrollView.contentOffset.y) animated:YES];
+ }
+ }
+ }
+ } else {
+ CGRect newFrame = _firstVisibleView.frame;
+ CGFloat deltaY = newFrame.origin.y - _prevFirstVisibleFrame.origin.y;
+ if (ABS(deltaY) > 0.5) {
+ CGFloat y = _scrollView.contentOffset.y;
+ [self _forceDispatchNextScrollEvent];
+ _scrollView.contentOffset = CGPointMake(_scrollView.contentOffset.x, _scrollView.contentOffset.y + deltaY);
+ if (autoscrollThreshold) {
+ // If the offset WAS within the threshold of the start, animate to the start.
+ if (y <= autoscrollThreshold.value()) {
+ [self scrollToOffset:CGPointMake(_scrollView.contentOffset.x, 0) animated:YES];
+ }
+ }
+ }
+ }
+}
+
 @end
 
 Class<RCTComponentViewProtocol> RCTScrollViewCls(void)

ReactCommon/react/renderer/components/scrollview/ScrollViewProps.cpp

@@ -127,6 +127,15 @@ ScrollViewProps::ScrollViewProps(
  "keyboardDismissMode",
  sourceProps.keyboardDismissMode,
  {})),
+ maintainVisibleContentPosition(
+ CoreFeatures::enablePropIteratorSetter
+ ? sourceProps.maintainVisibleContentPosition
+ : convertRawProp(
+ context,
+ rawProps,
+ "maintainVisibleContentPosition",
+ sourceProps.maintainVisibleContentPosition,
+ {})),
  maximumZoomScale(
  CoreFeatures::enablePropIteratorSetter
  ? sourceProps.maximumZoomScale
@@ -337,6 +346,7 @@ void ScrollViewProps::setProp(
  RAW_SET_PROP_SWITCH_CASE_BASIC(directionalLockEnabled);
  RAW_SET_PROP_SWITCH_CASE_BASIC(indicatorStyle);
  RAW_SET_PROP_SWITCH_CASE_BASIC(keyboardDismissMode);
+ RAW_SET_PROP_SWITCH_CASE_BASIC(maintainVisibleContentPosition);
  RAW_SET_PROP_SWITCH_CASE_BASIC(maximumZoomScale);
  RAW_SET_PROP_SWITCH_CASE_BASIC(minimumZoomScale);
  RAW_SET_PROP_SWITCH_CASE_BASIC(scrollEnabled);
@@ -413,6 +423,10 @@ SharedDebugStringConvertibleList ScrollViewProps::getDebugProps() const {
  "keyboardDismissMode",
  keyboardDismissMode,
  defaultScrollViewProps.keyboardDismissMode),
+ debugStringConvertibleItem(
+ "maintainVisibleContentPosition",
+ maintainVisibleContentPosition,
+ defaultScrollViewProps.maintainVisibleContentPosition),
  debugStringConvertibleItem(
  "maximumZoomScale",
  maximumZoomScale,

ReactCommon/react/renderer/components/scrollview/ScrollViewProps.h

@@ -11,6 +11,8 @@
 #include <react/renderer/components/view/ViewProps.h>
 #include <react/renderer/core/PropsParserContext.h>
 
+#include <optional>
+
 namespace facebook {
 namespace react {
 
@@ -43,6 +45,8 @@ class ScrollViewProps final : public ViewProps {
  bool directionalLockEnabled{};
  ScrollViewIndicatorStyle indicatorStyle{};
  ScrollViewKeyboardDismissMode keyboardDismissMode{};
+ std::optional<ScrollViewMaintainVisibleContentPosition>
+ maintainVisibleContentPosition{};
  Float maximumZoomScale{1.0f};
  Float minimumZoomScale{1.0f};
  bool scrollEnabled{true};

ReactCommon/react/renderer/components/scrollview/conversions.h

@@ -10,6 +10,7 @@
 #include <folly/dynamic.h>
 #include <react/renderer/components/scrollview/primitives.h>
 #include <react/renderer/core/PropsParserContext.h>
+#include <react/renderer/core/propsConversions.h>
 
 namespace facebook {
 namespace react {
@@ -98,6 +99,26 @@ inline void fromRawValue(
  abort();
 }
 
+inline void fromRawValue(
+ const PropsParserContext &context,
+ const RawValue &value,
+ ScrollViewMaintainVisibleContentPosition &result) {
+ auto map = (butter::map<std::string, RawValue>)value;
+
+ auto minIndexForVisible = map.find("minIndexForVisible");
+ if (minIndexForVisible != map.end()) {
+ fromRawValue(
+ context, minIndexForVisible->second, result.minIndexForVisible);
+ }
+ auto autoscrollToTopThreshold = map.find("autoscrollToTopThreshold");
+ if (autoscrollToTopThreshold != map.end()) {
+ fromRawValue(
+ context,
+ autoscrollToTopThreshold->second,
+ result.autoscrollToTopThreshold);
+ }
+}
+
 inline std::string toString(const ScrollViewSnapToAlignment &value) {
  switch (value) {
  case ScrollViewSnapToAlignment::Start:
@@ -109,6 +130,8 @@ inline std::string toString(const ScrollViewSnapToAlignment &value) {
  }
 }
 
+#if RN_DEBUG_STRING_CONVERTIBLE
+
 inline std::string toString(const ScrollViewIndicatorStyle &value) {
  switch (value) {
  case ScrollViewIndicatorStyle::Default:
@@ -144,5 +167,17 @@ inline std::string toString(const ContentInsetAdjustmentBehavior &value) {
  }
 }
 
+inline std::string toString(
+ const std::optional<ScrollViewMaintainVisibleContentPosition> &value) {
+ if (!value) {
+ return "null";
+ }
+ return "{minIndexForVisible: " + toString(value.value().minIndexForVisible) +
+ ", autoscrollToTopThreshold: " +
+ toString(value.value().autoscrollToTopThreshold) + "}";
+}
+
+#endif
+
 } // namespace react
 } // namespace facebook

ReactCommon/react/renderer/components/scrollview/primitives.h

@@ -7,6 +7,8 @@
 
 #pragma once
 
+#include <optional>
+
 namespace facebook {
 namespace react {
 
@@ -23,5 +25,20 @@ enum class ContentInsetAdjustmentBehavior {
  Always
 };
 
+class ScrollViewMaintainVisibleContentPosition final {
+ public:
+ int minIndexForVisible{0};
+ std::optional<int> autoscrollToTopThreshold{};
+
+ bool operator==(const ScrollViewMaintainVisibleContentPosition &rhs) const {
+ return std::tie(this->minIndexForVisible, this->autoscrollToTopThreshold) ==
+ std::tie(rhs.minIndexForVisible, rhs.autoscrollToTopThreshold);
+ }
+
+ bool operator!=(const ScrollViewMaintainVisibleContentPosition &rhs) const {
+ return !(*this == rhs);
+ }
+};
+
 } // namespace react
 } // namespace facebook

ReactCommon/react/renderer/debug/DebugStringConvertible.h

@@ -9,6 +9,7 @@
 
 #include <climits>
 #include <memory>
+#include <optional>
 #include <string>
 #include <unordered_set>
 #include <vector>
@@ -98,6 +99,14 @@ std::string toString(float const &value);
 std::string toString(double const &value);
 std::string toString(void const *value);
 
+template <typename T>
+std::string toString(const std::optional<T> &value) {
+ if (!value) {
+ return "null";
+ }
+ return toString(value.value());
+}
+
 /*
  * *Informal* `DebugStringConvertible` interface.
  *

packages/rn-tester/js/examples/ScrollView/ScrollViewExample.js

@@ -76,7 +76,7 @@ class AppendingList extends React.Component<
  <ScrollView
  automaticallyAdjustContentInsets={false}
  maintainVisibleContentPosition={{
- minIndexForVisible: 1,
+ minIndexForVisible: 0,
  autoscrollToTopThreshold: 10,
  }}
  nestedScrollEnabled