Flutter 字符串多余n行折叠，点击展开

TextPainter fetchTextPainter(String text, TextStyle style, int maxLine,
     double minWidth, double maxWidth) {
   return TextPainter(
       maxLines: maxLine,
       text: TextSpan(text: text, style: style),
       textDirection: TextDirection.ltr)
     ..layout(maxWidth: maxWidth, minWidth: minWidth);
 }

bool isExpansion(String text, TextStyle style, int maxLine, double minWidth,
      double maxWidth) {
    TextPainter _textPainter =
        fetchTextPainter(text, style, maxLine, minWidth, maxWidth);
    if (_textPainter.didExceedMaxLines) {
      //这里判断 文本是否截断
      return true;
    } else {
      return false;
    }
  }

String expansionString(String text, TextStyle style, int maxLine,
    double minWidth, double maxWidth) {
  TextPainter _textPainter =
      fetchTextPainter(text, style, maxLine, minWidth, maxWidth);
  var end = _textPainter
      .getPositionForOffset(
          Offset(_textPainter.size.width, _textPainter.size.height))
      .offset;
  return text.substring(0, end - 2) + "...";
}