Use the concept of '_ controller. onDelete' to set the value of '_ handleDelete'; Deleting UTF-16 emoticons doesn't work properly, what should I do

[zhaofeixaing]

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The question

Use the concept of '_ controller. onDelete' to set the value of '_ handleDelete'; Deleting UTF-16 emoticons doesn't work properly, what should I do
新标签页 - Awesome Screenshot - Awesome Screenshot.webm
这个是我的代码

 @override
  void initState() {
    super.initState();
    _controller.document = widget.args.document;

    _controller.onDelete = _handleDelete;
    // textEditingValue
  }

  void _handleDelete(int cursorPosition, bool forward) {
    print('Delete at position: $cursorPosition, forward: $forward');
    final doc = _controller.document.toPlainText();
    final characters = doc.characters;

    if (forward) {
      if (cursorPosition < characters.length) {
        final newText = characters.take(cursorPosition).toString() + characters.skip(cursorPosition + 1).toString();
        _controller.replaceText(
          cursorPosition,
          1,
          '',
          TextSelection.collapsed(offset: cursorPosition),
        );
      }
    } else {
      if (cursorPosition > 0) {
        final newText = characters.take(cursorPosition - 1).toString() + characters.skip(cursorPosition).toString();
        _controller.replaceText(
          cursorPosition - 1,
          1,
          '',
          TextSelection.collapsed(offset: cursorPosition - 1),
        );
      }
    }
  }

Running error

════════ Exception caught by painting library ══════════════════════════════════
The following ArgumentError was thrown while building a TextSpan:
Invalid argument(s): string is not well-formed UTF-16