Flutter expandable text step 1

expandable_3.dart

class ExpandableText extends StatefulWidget {
  final TextSpan textSpan;
  final TextSpan moreSpan;
  final int maxLines;

  const ExpandableText({
    Key key,
    this.textSpan,
    this.maxLines,
    this.moreSpan,
  })
      : assert(textSpan != null),
        assert(maxLines != null),
        assert(moreSpan != null),
        super(key: key);

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

class _ExpandableTextState extends State<ExpandableText> {
  static const String _ellipsis = "\u2026\u0020"; // Unicode symbols for "… "

  bool _isExpanded = false;

  GestureRecognizer get _tapRecognizer => TapGestureRecognizer()
    ..onTap = () {
      setState(() {
        _isExpanded = !_isExpanded;
      });
    };

  @override
  Widget build(BuildContext context) => LayoutBuilder(
        builder: (context, constraints) {
          // TODO: we'll do some maths here
        },
      );
}