network_resource 0.2.1

Automatically cache network resources and use them when offline.

network_resource

Automatically cache network resources and use them when offline.

NetworkResource fetches data over HTTP, caches it in a file, and holds it in memory. The main method, get(), will return the value in memory, cache, or fetch from the network -- in that order. If the cache file is older than maxAge, the cache will be updated from the network if available. To manually refresh, use get(forceReload: true) or getFromNetwork(). The latter can be used to avoid cache fallback.

Examples

There are three concrete classes included.

• StringNetworkResource
• StringListNetworkResource
• BinaryNetworkResource

// String data.
final eventsResource = StringNetworkResource(
  url: 'https://example.com/events.json',
  cacheFile: File('events.json'),
  maxAge: Duration(minutes: 60),
);

// Binary data.
final photo = BinaryNetworkResource(
  url: 'https://example.com/photo.png',
  cacheFile: File('photo.png'),
  maxAge: Duration(hours: 24),
);

// A string list, line by line.
 final words = StringListNetworkResource(
  url: 'https://example.com/wordlist.txt',
  cacheFile: File('wordlist.txt'),
  maxAge: Duration(hours: 24),
);

// Parsing a JSON string into a `List<Event>`.
json.decode(data).forEach((item) => events.add(Event(item)));

Extend

Instead of declaring the resource and parsing its data separately, extend the base class and implement parseContents(contents) where either a String or List<int> will be passed, depending on the value of isBinary.

While this example uses Flutter, the package is not dependent on Flutter. If you are using Flutter, try the path provider package to help specify where the cache file should be located.

// This example subclasses `NetworkResource` to manage fetching and parsing
// an event list in JSON format. Items are shown in a list with pull-to-refresh.

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:network_resource/network_resource.dart';

class Event {
  final String title;
  Event(this.title);
}

class EventListResource extends NetworkResource<List<Event>> {
  EventListResource()
      : super(
            url: 'http://example.com/events.json',
            cacheFile: File('events.json'),
            maxAge: Duration(minutes: 60),
            isBinary: false);
  @override
  List<Event> parseContents(contents) {
    List events;
    json.decode(contents).forEach((item) => events.add(Event(item)));
    return events;
  }
}

final eventsResource = EventListResource();

class _EventListState extends State<EventList> {
  Future<Null> refresh() async {
    await eventsResource.get(forceReload: true);
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: RefreshIndicator(
            onRefresh: refresh,
            child: ListView.builder(
                itemBuilder: (context, index) =>
                    Text(eventsResource.data[index].title))));
  }
}

class EventList extends StatefulWidget {
  @override
  _EventListState createState() => _EventListState();
}

void main() => runApp(MaterialApp(
    title: 'Network Resource example',
    home: FutureBuilder<List<Event>>(
      future: eventsResource.get(),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return EventList();
        } else if (snapshot.hasError) {
          return Text('${snapshot.error}');
        }
        return Center(child: CircularProgressIndicator());
      },
    )));