have an tooltip in some word of my textfield

Question

i want to have tooltip on some word in my textfield so i extended my TextEdditingController so he can convert the word underline to an word with a tooltip but now the cursor have positions problems

This is my class TextEdditingController :

class MyTextEditingController extends TextEditingController {
  final GlobalKey _key;
  MyTextEditingController(this._key);
  @override
  TextSpan buildTextSpan({
    required BuildContext context,
    TextStyle? style,
    required bool withComposing,
  }) {
    final text = this.text;
    final List<InlineSpan> textSpanChildren = [];
    text.splitMapJoin(RegExp('underline'), onMatch: (m) {
      final String underlinedText = m.group(0)!;

      textSpanChildren.add(WidgetSpan(
          child: Tooltip(
            preferBelow: false,
            message: 'the message',
            child: Text(
                    underlinedText,
                    style: style?.merge(const TextStyle(
              decoration: TextDecoration.underline, color: Colors.blue)),
                  ),
          )));
      return '';
    }, onNonMatch: (text) {
      textSpanChildren.add(TextSpan(text: text, style: style));
      return '';
    });

    return TextSpan(style: style, children: textSpanChildren);
  }
}