[iOS][TextInput] Apply the fix for CJK languages on single-line text …

…fields.

Libraries/Text/TextInput/Singleline/RCTUITextField.m

@@ -14,6 +14,7 @@
 
 @implementation RCTUITextField {
   RCTBackedTextFieldDelegateAdapter *_textInputDelegateAdapter;
+  NSMutableAttributedString *_attributesHolder;
 }
 
 - (instancetype)initWithFrame:(CGRect)frame
@@ -25,6 +26,7 @@ - (instancetype)initWithFrame:(CGRect)frame
                                                object:self];
 
     _textInputDelegateAdapter = [[RCTBackedTextFieldDelegateAdapter alloc] initWithTextField:self];
+    _attributesHolder = [[NSMutableAttributedString alloc] init];
   }
 
   return self;
@@ -107,6 +109,37 @@ - (CGRect)caretRectForPosition:(UITextPosition *)position
   return [super caretRectForPosition:position];
 }
 
+#pragma mark - Fix for CJK Languages
+// Search for `GH-19339` to see all code affected by this fix.
+
+- (void)setAttributedText:(NSAttributedString *)attributedText {
+  // Using `setAttributedString:` while user is typing breaks some internal mechanics
+  // when entering complex input languages such as Chinese, Korean or Japanese.
+  // see: https://github.com/facebook/react-native/issues/19339
+
+  // We try to avoid calling this method as much as we can.
+  BOOL textWasChanged = ![_attributesHolder.string isEqualToString:attributedText.string];
+
+  // We update attributes only if possible.
+  [_attributesHolder setAttributedString:attributedText];
+
+  // If the text has changed, there is nothing we can do.
+  if (textWasChanged) {
+    [super setAttributedText:attributedText];
+  }
+}
+
+- (NSAttributedString *)attributedText {
+  // For the text contents `super.attributedText.string` is the source of truth.
+  // If it differs, we match our internal state to it.
+  if(![super.attributedText.string isEqualToString:_attributesHolder.string]) {
+    [_attributesHolder setAttributedString:super.attributedText];
+  }
+
+  // For the text attributes, our internal state is the source of truth.
+  return _attributesHolder;
+}
+
 #pragma mark - Positioning Overrides
 
 - (CGRect)textRectForBounds:(CGRect)bounds