use setstate in stateless code example

Example 1: setstate flutter

setState(() { _myState = newValue; });

Example 2: stateless widget flutter

class GreenFrog extends StatelessWidget {
  const GreenFrog({ Key key }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(color: const Color(0xFF2DBD3A));
  }
}