如何在结尾处显示更多的文本来代替TextOverflow.ellipsis inFlutter？

import 'package:flutter/material.dart';

class ExpandableText extends StatefulWidget {
  final String text;
  final int maxLines;

  ExpandableText({required this.text, required this.maxLines});

  @override
  _ExpandableTextState createState() => _ExpandableTextState();
}

class _ExpandableTextState extends State<ExpandableText> {
  bool isExpanded = false;

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (context, constraints) {
        final textSpan = TextSpan(
          text: widget.text,
          style: DefaultTextStyle.of(context).style,
        );

        final textPainter = TextPainter(
          text: textSpan,
          maxLines: widget.maxLines,
          textDirection: TextDirection.ltr,
        );
        textPainter.layout(maxWidth: constraints.maxWidth);

        if (textPainter.didExceedMaxLines) {
          return Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
              RichText(
                text: TextSpan(
                  text: isExpanded ? widget.text : widget.text.substring(0, textPainter.getPositionForOffset(Offset(constraints.maxWidth, constraints.maxHeight)).offset),
                  style: DefaultTextStyle.of(context).style,
                ),
              ),
              GestureDetector(
                onTap: () {
                  setState(() {
                    isExpanded = !isExpanded;
                  });
                },
                child: Text(
                  isExpanded ? '收起' : '展开',
                  style: TextStyle(
                    color: Colors.blue,
                    fontWeight: FontWeight.bold,
                  ),
                ),
              ),
            ],
          );
        } else {
          return Text(widget.text);
        }
      },
    );
  }
}

ExpandableText(
  text: '这是一段很长的文本...',
  maxLines: 2,
)