Deprecated in favor of async_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.
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'),
);
// Parsing a JSON string into a `List<Event>`.
json.decode(data).forEach((item) => events.add(Event(item)));
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());
},
)));