Passing Data from child widget to parent widget

main.dart

import 'package:flutter/material.dart';
class Article {
  String name, detail;
  Article(this.name, this.detail);
}

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  final articleList = List<Article>.generate(20, (i) {
    return Article("Article number $i", "This is the detail of article $i");
  });

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Scaffold(
            appBar: AppBar(
            title: Text("Flutter List View with Divider"),
            ),
            body: Builder(
                builder: (BuildContext context) {

                return MyList(articleList, (index) {
                                final snackBar = SnackBar(content: Text('List Item $index is Clicked'));
                                Scaffold.of(context).showSnackBar(snackBar);
                          }
                       );
                },
          ),
        )
    );
  }
}

class MyList extends StatelessWidget {
  final articles;
  final ValueSetter<int> onItemTap;

  MyList(this.articles, this.onItemTap);

  @override
  Widget build(BuildContext context) {
    return ListView.separated(
        itemBuilder: (BuildContext context, int index) {
          return ListTile(
            title: Text(articles[index].name),
            subtitle: Text(articles[index].detail),
            onTap: () {
              onItemTap(index);
            },
          );
        },
        separatorBuilder: (BuildContext context, int index) => Divider(),
        itemCount: articles.length
    );
  }
}