package:angel_client support for "realtime" interactions with Angel via long polling.
Angel supports WebSockets on the server and client, which makes it very straightforward to implement realtime collections. However, not every user's browser supports WebSockets. In such a case, applications might gracefully degrade to long-polling the server for changes.
A PollingService wraps a client-side Service (typically a REST-based one), and calls its
index method at a regular interval. After indexing, the PollingService performs a diff
and identifies whether items have been created, modified, or removed. The updates are sent out
through onCreated, onModified, etc., effectively managing a real-time collection of data.
A common use-case would be passing this service to ServiceList, a class that manages the state
of a collection managed in real-time.
import 'package:angel_client/io.dart';
import 'package:angel_poll/angel_poll.dart';
main() {
var app = new Rest('http://localhost:3000');
var todos = new ServiceList(
new PollingService(
// Typically, you'll pass a REST-based service instance here.
app.service('api/todos'),
// `index` called every 5 seconds
const Duration(seconds: 5),
),
);
todos.onChange.listen((_) {
// Something happened here.
// Maybe an item was created, modified, etc.
});
}