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Keep iOS text line breaks stable while LayoutAnimation resizes a paragraph #59162

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Keep iOS text line breaks stable while LayoutAnimation resizes a paragraph #59162

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7 changes: 7 additions & 0 deletions packages/react-native/React/Fabric/Mounting/ComponentViews/Text/RCTParagraphComponentView.mm
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Original file line number Diff line number Diff line change
Expand Up @@ -188,6 +188,13 @@ - (void)_updateTextViewFrame
CGRect textViewFrame = self.bounds;
CGRect drawingFrame = RCTCGRectFromRect(_layoutMetrics.getContentFrame());

// Lay out the text in the size the paragraph has in the shadow tree rather than in the current frame, which
// LayoutAnimation interpolates. Otherwise, line breaks change on every frame and words jump between lines.
// The text view clips the text to the current bounds.
if (_textView.state) {
drawingFrame.size = RCTCGSizeFromSize(_textView.state->getData().layoutSize);
}

if (ReactNativeFeatureFlags::enableIOSCompressedTextFrameAdjustment() && _textView.state &&
drawingFrame.size.height > 0) {
const auto &stateData = _textView.state->getData();
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15 changes: 15 additions & 0 deletions packages/react-native/ReactCommon/react/renderer/components/text/ParagraphShadowNode.cpp
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Expand Up @@ -178,6 +178,7 @@ void ParagraphShadowNode::updateStateIfNeeded(const Content& content) {
auto& state = getStateData();

react_native_assert(textLayoutManager_);
#ifdef ANDROID
if (state.attributedString == content.attributedString) {
return;
}
Expand All @@ -187,6 +188,20 @@ void ParagraphShadowNode::updateStateIfNeeded(const Content& content) {
content.attributedString,
content.paragraphAttributes,
textLayoutManager_});
#else
auto layoutSize = getLayoutMetrics().getContentFrame().size;
if (state.attributedString == content.attributedString &&
state.layoutSize == layoutSize) {
return;
}

setStateData(
ParagraphState{
content.attributedString,
content.paragraphAttributes,
textLayoutManager_,
layoutSize});
#endif
}

MeasuredPreparedTextLayout* ParagraphShadowNode::findUsableLayout() {
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4 changes: 2 additions & 2 deletions packages/react-native/ReactCommon/react/renderer/components/text/ParagraphShadowNode.h
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Expand Up @@ -110,8 +110,8 @@ class ParagraphShadowNode
void updateStateIfNeeded(const Content &content, const MeasuredPreparedTextLayout &layout);

/*
* Creates a `State` object (with `AttributedText` and
* `TextLayoutManager`) if needed.
* Creates a `State` object (with `AttributedText`, `TextLayoutManager` and,
* outside of Android, the size of the content frame) if needed.
*/
void updateStateIfNeeded(const Content &content);

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9 changes: 9 additions & 0 deletions ...act/renderer/components/text/platform/cxx/react/renderer/components/text/ParagraphState.h
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Expand Up @@ -10,6 +10,7 @@
#include <react/cxxstableapi/FrameworksGuard.h>

#include <React/Debug.h>
#include <React/Graphics.h>
#include <react/renderer/attributedstring/AttributedString.h>
#include <react/renderer/attributedstring/ParagraphAttributes.h>
#include <react/renderer/textlayoutmanager/TextLayoutManager.h>
Expand Down Expand Up @@ -39,6 +40,14 @@ class ParagraphState final {
* `AttributedString`.
*/
std::weak_ptr<const TextLayoutManager> layoutManager;

/*
* Size of the content frame that the paragraph was laid out with.
* The mounted view can temporarily have a different size (e.g. while
* LayoutAnimation interpolates its frame), so it lays out text in this size
* to keep line breaks stable.
*/
Size layoutSize;
};

} // namespace facebook::react
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