gender_card.dart

class _GenderCardState extends State<GenderCard> with SingleTickerProviderStateMixin {
  AnimationController _arrowAnimationController; //<--- Add controller
  Gender selectedGender;

  @override
  void initState() {
    selectedGender = widget.initialGender ?? Gender.other;
    _arrowAnimationController = new AnimationController( //<--- initialize animation controller
      vsync: this,
      lowerBound: -_defaultGenderAngle,
      upperBound: _defaultGenderAngle,
      value: _genderAngles[selectedGender],
    );
    super.initState();
  }

  @override
  void dispose() {
    _arrowAnimationController.dispose(); //<--- dispose controller when we're done
    super.dispose();
  }

  Widget _drawCircleIndicator() {
    return Stack(
      alignment: Alignment.center,
      children: <Widget>[
        GenderCircle(),
        GenderArrow(listenable: _arrowAnimationController), //<--- Update constructor
      ],
    );
  }

  _drawGestureDetector() {
    return Positioned.fill(
      child: TapHandler(
        onGenderTapped: _setSelectedGender, //<--- Update tap handling
      ),
    );
  }

  void _setSelectedGender(Gender gender) {
    setState(() => selectedGender = gender);
    _arrowAnimationController.animateTo( //<--- Animate the arrow
      _genderAngles[gender],
      duration: Duration(milliseconds: 150),
    );
  }
}


class GenderArrow extends AnimatedWidget { //<--- Use AnimatedWidget
  const GenderArrow({Key key, Listenable listenable}) : super(key: key, listenable: listenable);

  @override
  Widget build(BuildContext context) {
    Animation animation = listenable;
    return Transform.rotate(
      angle: animation.value, //<--- use animation value
      ...
    );
  }
}