autocorrect_underline.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: Text('Sample App')),
        body: CustomEditableText(),
      ),
    );
  }
}

class CustomEditableText extends StatefulWidget {
  @override
  _CustomEditableTextState createState() => _CustomEditableTextState();
}

class _CustomEditableTextState extends State<CustomEditableText> {
  final NoUnderlineTextEditingController _controller =
      NoUnderlineTextEditingController(decorationColor: Colors.green);

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: EditableText(
        controller: _controller,
        focusNode: FocusNode(),
        style: TextStyle(fontSize: 18, color: Colors.black),
        cursorColor: Colors.blue,
        backgroundCursorColor: Colors.grey,
        keyboardType: TextInputType.multiline,
        minLines: 1,
        maxLines: null,
        autocorrect: true,
      ),
    );
  }
}

class NoUnderlineTextEditingController extends TextEditingController {
  final Color decorationColor;

  NoUnderlineTextEditingController({required this.decorationColor});

  TextSpan buildTextSpan(
      {required BuildContext context,
      TextStyle? style,
      required bool withComposing}) {
    assert(!value.composing.isValid ||
        !withComposing ||
        value.isComposingRangeValid);
    final bool composingRegionOutOfRange =
        !value.isComposingRangeValid || !withComposing;

    if (composingRegionOutOfRange) {
      return TextSpan(style: style, text: text);
    }

    final TextStyle composingStyle = style?.merge(TextStyle(
          decoration: TextDecoration.underline,
          decorationColor: decorationColor,
        )) ??
        TextStyle(
            decoration: TextDecoration.underline,
            decorationColor: decorationColor);
    return TextSpan(
      style: style,
      children: <TextSpan>[
        TextSpan(text: value.composing.textBefore(value.text)),
        TextSpan(
          style: composingStyle,
          text: value.composing.textInside(value.text),
        ),
        TextSpan(text: value.composing.textAfter(value.text)),
      ],
    );
  }
}