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fix(ios): keep a zoomed ScrollView usable when its content size changes #58498

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fix(ios): keep a zoomed ScrollView usable when its content size changes #58498

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13 changes: 11 additions & 2 deletions ...eact-native/React/Fabric/Mounting/ComponentViews/ScrollView/RCTScrollViewComponentView.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -495,10 +495,19 @@ - (void)updateState:(const State::Shared &)state oldState:(const State::Shared &
}

_contentSize = contentSize;
_containerView.frame = CGRect{RCTCGPointFromPoint(data.contentBoundingRect.origin), contentSize};

// `_containerView` is the scroll view's zooming view (see `viewForZoomingInScrollView:`), so while the user is
// pinch-zoomed in it carries a scale transform. Setting `frame` on a view whose `transform` is not the identity is
// undefined behavior, so lay it out through `bounds` and `center` instead. The scroll view must get the *zoomed*
// size, which is what UIScrollView itself keeps `contentSize` at while zooming.
CGPoint contentOrigin = RCTCGPointFromPoint(data.contentBoundingRect.origin);
_containerView.bounds = CGRect{CGPointZero, contentSize};
CGSize zoomedContentSize = _containerView.frame.size;
_containerView.center =
CGPoint{contentOrigin.x + zoomedContentSize.width / 2, contentOrigin.y + zoomedContentSize.height / 2};

[self _preserveContentOffsetIfNeededWithBlock:^{
self->_scrollView.contentSize = contentSize;
self->_scrollView.contentSize = zoomedContentSize;
}];
}

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