Flutter expandable text step 2

expandable_4.dart

extension _TextMeasurer on RichText {
  List<TextBox> measure(BuildContext context, Constraints constraints) {
    final renderObject = createRenderObject(context)..layout(constraints);
    return renderObject.getBoxesForSelection(
      TextSelection(
        baseOffset: 0,
        extentOffset: text.toPlainText().length,
      ),
    );
  }
}
class _ExpandableTextState extends State<ExpandableText> {
  // ...

  @override
  Widget build(BuildContext context) => LayoutBuilder(
        builder: (context, constraints) {
          final maxLines = widget.maxLines;

          final richText = Text.rich(widget.textSpan).build(context) as RichText;
          final boxes = richText.measure(context, constraints);

          if (boxes.length <= maxLines || _isExpanded) {
            return RichText(text: widget.textSpan);
          } else {
            // TODO: deal with ellipsized text
          }
        },
      );
}