1.On Child Widget : add parameter Function paramter
class ChildWidget extends StatefulWidget {
final Function() notifyParent;
ChildWidget({Key key, @required this.notifyParent}) : super(key: key);
}
2.On Parent Widget : create a Function for the child to callback
refresh() {
setState(() {});
}
3.On Parent Widget : pass parentFunction to Child Widget
new ChildWidget( notifyParent: refresh );
4.On Child Widget : call the Parent Function
widget.notifyParent();