@override
Widget build(BuildContext context) {
  return NestedScrollView(
    headerSliverBuilder: (context, innerBoxScrolled) => [
          SliverAppBar(
            title: Text('POSTAPP'),
            centerTitle: true,
            floating: true,
            pinned: false,
          ),
        ],
    body: RefreshIndicator(
      onRefresh: _loadMorePosts,
      child: ListView.builder(
        itemBuilder: _createPostItem,
        itemCount: _postsCount,
      ),
    ),
  );
}