From 89f4dd2a243dd1255bf2ced3a694ffc62b7aa3fd Mon Sep 17 00:00:00 2001
From: Wang Chuan <ouchuanm@outlook.com>
Date: Mon, 14 Apr 2025 05:42:24 -0700
Subject: [PATCH] fix(ios): avoid incorrectly updating caret position (#50680)

Summary:
Avoid incorrectly updating caret position

Pull Request resolved: https://github.com/facebook/react-native/issues/50641

The caret position is updated incorrectly when a user is first typing if an zero-length selection is set.

[IOS] [CHANGED] - Typing into TextInput now will not cause the caret position to update to the beginning when a zero-length selection is set.

Pull Request resolved: https://github.com/facebook/react-native/pull/50680

Test Plan:
Tested with the following code(a simplified version from the code in https://github.com/facebook/react-native/issues/50641)
```js
const [selection, setSelection] = useState({start: -1, end: -1});
const onSelectionChange = (
      evt: NativeSyntheticEvent<TextInputSelectionChangeEventData>,
    ) => {
      const {selection} = evt.nativeEvent;
      const {start, end} = selection;
      console.log('selection change: ', start, end);
      setSelection(selection);
};
return (
  <View style={{ position: 'absolute', top: 50, left: 30 }}>
    <TextInput
      placeholder="test"
      selection={selection}
      onSelectionChange={onSelectionChange}
    />
  </View>
);
```
When using the main branch, the caret position will jump back to the beginning after the first typing.
It works fine after applying this commit.

Reviewed By: fabriziocucci

Differential Revision: D72957245

Pulled By: cipolleschi

fbshipit-source-id: 3586797332b35e86b17f386a35e7d192ff758f7e
---
 .../TextInput/RCTTextInputComponentView.mm    | 35 ++++++++++++-------
 1 file changed, 22 insertions(+), 13 deletions(-)

diff --git a/packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm b/packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm
index dd03c96ea91..e1cad8a3f1f 100644
--- a/packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm
+++ b/packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm
@@ -698,6 +698,11 @@ static NSSet<NSNumber *> *returnKeyTypesSet;
 }
 
 - (void)_restoreTextSelection
+{
+  [self _restoreTextSelectionAndIgnoreCaretChange:NO];
+}
+
+- (void)_restoreTextSelectionAndIgnoreCaretChange:(BOOL)ignore
 {
   const auto &selection = static_cast<const TextInputProps &>(*_props).selection;
   if (!selection.has_value()) {
@@ -707,6 +712,9 @@ static NSSet<NSNumber *> *returnKeyTypesSet;
                                                    offset:selection->start];
   auto end = [_backedTextInputView positionFromPosition:_backedTextInputView.beginningOfDocument offset:selection->end];
   auto range = [_backedTextInputView textRangeFromPosition:start toPosition:end];
+  if (ignore && range.empty) {
+    return;
+  }
   [_backedTextInputView setSelectedTextRange:range notifyDelegate:YES];
 }
 
@@ -721,19 +729,20 @@ static NSSet<NSNumber *> *returnKeyTypesSet;
   // Updating the UITextView attributedText, for example changing the lineHeight, the color or adding
   // a new paragraph with \n, causes the cursor to move to the end of the Text and scroll.
   // This is fixed by restoring the cursor position and scrolling to that position (iOS issue 652653).
-  if (selectedRange.empty) {
-    // Maintaining a cursor position relative to the end of the old text.
-    NSInteger offsetStart = [_backedTextInputView offsetFromPosition:_backedTextInputView.beginningOfDocument
-                                                          toPosition:selectedRange.start];
-    NSInteger offsetFromEnd = oldTextLength - offsetStart;
-    NSInteger newOffset = attributedString.string.length - offsetFromEnd;
-    UITextPosition *position = [_backedTextInputView positionFromPosition:_backedTextInputView.beginningOfDocument
-                                                                   offset:newOffset];
-    [_backedTextInputView setSelectedTextRange:[_backedTextInputView textRangeFromPosition:position toPosition:position]
-                                notifyDelegate:YES];
-    [_backedTextInputView scrollRangeToVisible:NSMakeRange(offsetStart, 0)];
-  }
-  [self _restoreTextSelection];
+  // Maintaining a cursor position relative to the end of the old text.
+  NSInteger offsetStart = [_backedTextInputView offsetFromPosition:_backedTextInputView.beginningOfDocument
+                                                        toPosition:selectedRange.start];
+  NSInteger offsetFromEnd = oldTextLength - offsetStart;
+  NSInteger newOffset = attributedString.string.length - offsetFromEnd;
+  UITextPosition *position = [_backedTextInputView positionFromPosition:_backedTextInputView.beginningOfDocument
+                                                                 offset:newOffset];
+  [_backedTextInputView setSelectedTextRange:[_backedTextInputView textRangeFromPosition:position toPosition:position]
+                              notifyDelegate:YES];
+  [_backedTextInputView scrollRangeToVisible:NSMakeRange(offsetStart, 0)];
+
+  // A zero-length selection range can cause the caret position to change on iOS,
+  // and we have already updated the caret position, so we can safely ignore caret changing in this place.
+  [self _restoreTextSelectionAndIgnoreCaretChange:YES];
   [self _updateTypingAttributes];
   _lastStringStateWasUpdatedWith = attributedString;
 }