Avoid using -[UITextView setAttributedString:] while user is typing text.

For languages with complex input (such as Japanese or Chinese),
where user presses multiple buttons to input one symbol,
it breaks selection and input, so it is impossible to enter characters.

Author: Igor Mandrigin

Libraries/Text/TextInput/Multiline/RCTUITextView.m

@@ -110,7 +110,21 @@ - (void)setTextAlignment:(NSTextAlignment)textAlignment
 
 - (void)setAttributedText:(NSAttributedString *)attributedText
 {
-  [super setAttributedText: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.
+  // If the text has changed, there is nothing we can do.
+  if (![super.attributedText.string isEqualToString:attributedText.string]) {
+    [super setAttributedText:attributedText];
+  } else {
+  // But if the text is preserved, we just copying the attributes from the source string.
+    if (![super.attributedText isEqualToAttributedString:attributedText]) {
+      [self copyTextAttributesFrom:attributedText];
+    }
+  }
+
   [self textDidChange];
 }
 
@@ -241,4 +255,20 @@ - (void)invalidatePlaceholderVisibility
   _placeholderView.hidden = !isVisible;
 }
 
+#pragma mark - Utility Methods
+
+- (void)copyTextAttributesFrom:(NSAttributedString *)sourceString
+{
+  [self.textStorage beginEditing];
+
+  NSTextStorage *textStorage = self.textStorage;
+  [sourceString enumerateAttributesInRange:NSMakeRange(0, sourceString.length)
+                                   options:NSAttributedStringEnumerationReverse
+                                usingBlock:^(NSDictionary<NSAttributedStringKey,id> * _Nonnull attrs, NSRange range, BOOL * _Nonnull stop) {
+                                  [textStorage setAttributes:attrs range:range];
+                                }];
+
+  [self.textStorage endEditing];
+}
+
 @end