Simple provider example

featured_post.dart

import 'package:flutter/material.dart';
import 'package:flutter_bloc/blocs/featured_post_bloc.dart';
import 'package:provider/provider.dart';

import 'package:flutter_bloc/widgets/refresh.dart';

class FeaturedPostPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final FeaturedPostBloc featuredPostBloc =
        Provider.of<FeaturedPostBloc>(context);

    if (featuredPostBloc.posts.length == 0) {
      featuredPostBloc.fetchPosts(); // It works but throws errors.
    }

    return Container(
      child: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            featuredPostBloc.isLoading
                ? CircularProgressIndicator()
                : Text(
                    featuredPostBloc.posts.length.toString(),
                    style: TextStyle(fontSize: 62.0),
                  ),
            RefreshButton(),
          ],
        ),
      ),
    );
  }
}

featured_post_bloc.dart

import 'package:flutter/material.dart';
import 'package:flutter_bloc/models/post.dart';
import 'dart:convert';
import 'package:http/http.dart' as http;

Future<List<Post>> _fetchPosts() async {
  final response = await http.get('https://api.kodilan.com/posts?get=25');

  if (response.statusCode == 200) {
    var body = json.decode(response.body);
    List<Object> list = body["data"];
    return list.map((item) => Post.fromJson(item)).toList();
  } else {
    throw Exception('Failed to load post');
  }
}

class FeaturedPostBloc extends ChangeNotifier {
  List<Post> _posts = [];
  bool _isLoading = false;
  bool _hasError = false;

  bool get hasError => _hasError;
  bool get isLoading => _isLoading;
  List<Post> get posts => _posts;

  set isLoading(bool isLoading) {
    _isLoading = isLoading;
    notifyListeners();
  }

  set hasError(bool hasError) {
    _hasError = hasError;
    notifyListeners();
  }

  set posts(List<Post> posts) {
    _posts = posts;
    notifyListeners();
  }

  fetchPosts() async {
    isLoading = true;
    hasError = false;
    try {
      posts = await _fetchPosts();
    } catch (e) {
      print(e);
      hasError = true;
    } finally {
      isLoading = false;
    }
  }
}