GridView Scroll Position Question Related Snippets

home_page.dart

class HomePage extends StatefulWidget {
  final MovieBloc bloc;

  HomePage({this.bloc});

  @override
  HomePageState createState() {
    return new HomePageState();
  }
}

class HomePageState extends State<HomePage> {
  int _currentIndex = 0;

  @override
  void dispose() {
    widget.bloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Home'),
      ),
      bottomNavigationBar: BottomNavigationBar(
        onTap: (index) {
          setState(() {
            _currentIndex = index;
          });
          if (index == 0) {
            widget.bloc.moviesType.add(MovieType.Popular);
          } else if (index == 1) {
            widget.bloc.moviesType.add(MovieType.TopRated);
          } else {
            widget.bloc.moviesType.add(MovieType.NowPlaying);
          }
        },
        currentIndex: _currentIndex,
        items: [
          BottomNavigationBarItem(
              icon: Icon(Icons.favorite), title: Text('Popular')),
          BottomNavigationBarItem(
              icon: Icon(Icons.star), title: Text('Top Rated')),
          BottomNavigationBarItem(
              icon: Icon(Icons.play_arrow), title: Text('Now Playing')),
        ],
      ),
      body: StreamBuilder<UnmodifiableListView<Movie>>(
          initialData: UnmodifiableListView<Movie>([]),
          stream: widget.bloc.movies,
          builder: (BuildContext context,
              AsyncSnapshot<UnmodifiableListView<Movie>> snapshot) {
            if (snapshot.hasData) {
              return MovieList(snapshot.data);
            } else if (snapshot.hasError) {
              return Center(child: Text(snapshot.error.toString()));
            } else {
              return Center(child: CircularProgressIndicator());
            }
          }),
    );
  }
}

movie_list.dart

import 'package:flutter/material.dart';
import 'package:popular_movies/model/movie.dart';
import 'package:popular_movies/pages/movie_item.dart';

class MovieList extends StatefulWidget {
  final List<Movie> movies;

  MovieList(this.movies);

  @override
  _MovieListState createState() {
    return new _MovieListState();
  }
}

class _MovieListState extends State<MovieList> {
  ScrollController _scrollController;

  @override
  void initState() {
    _scrollController = ScrollController();
    super.initState();
  }

  @override
  void didUpdateWidget(MovieList oldWidget) {
    print("didUpdateWidget MovieList");
    super.didUpdateWidget(oldWidget);
  }

  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      controller: _scrollController,
      itemCount: widget.movies.length,
      itemBuilder: (BuildContext context, int index) {
        return MovieItem(widget.movies[index]);
      },
      gridDelegate: new SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: 2,
        childAspectRatio: 2 / 3,
      ),
    );
  }
}