A control object responsible for managing subscription to server published collections.

Example

Create simple Subscriber and subscribe to collection of users.

 var subscriber = new Subscriber(connection);
 subscriber.init().then((value) {
   var usersSubscription = subscriber.subscribe("users", {"olderThan": 18});
   useUsers(usersSubscription.collection);
 });

class Subscriber {
 Connection _connection;
 String _idPrefix = null;
 final IdGenerator _subscriptionIdGenerator, _dataIdGenerator;
 final _createSubscription;

 /**
  * Dependency injection constructor used mainly in tests.
  */
 Subscriber.config(this._connection, this._dataIdGenerator,
          this._subscriptionIdGenerator, this._createSubscription);


 /**
  * Creates new instance communicating with server using the [connection].
  */
 Subscriber(connection) : this.config(connection, new IdGenerator(),
     new IdGenerator(), _defaultSubscriptionFactory);

 Future _loadIdPrefix() =>_connection.send(
       () => new ClientRequest("sync", {"action" : "get_id_prefix"})
   ).then((response) => response['id_prefix']);

 /**
  * Initialize the subscriber. Using [Subscriber] without proper initialization
  * results in [StateError].
  *
  * The method's purpose is to set an unique [idPrefix] that can be used in
  * '_id' generation in the client code. If the [init] is called without the
  * [idPrefix], it is requested from the server.
  *
  * This method returns the [Future] that completes when the [idPrefix] is
  * obtained and set.
  */
 Future init([idPrefix = null]) {
   idPrefix = (idPrefix == null) ?
       _loadIdPrefix() :
       new Future.value(idPrefix);

   return idPrefix.then((prefix) {
     _idPrefix = prefix;
     _subscriptionIdGenerator.prefix = prefix;
     _dataIdGenerator.prefix = prefix;
   });
 }

 /**
  * Subscribe to [collectionName] published on server. Subscriber must be
  * properly initialized with [init] method before calling [subscribe].
  *
  * Create new [Subscription] to published collection using its
  * [collectionName] and optionally [args]. Data in subscribed collection is
  * keeped in sync between the server and the client with no interaction
  * needed from the user.
  *
  * It is also possible to create multiple independend subscriptions with same
  * [collectionName] and/or [args]. This can be useful when subscribing to
  * really big collection and want to request only a portion of data specified
  * by [args].
  */
 Subscription subscribe(String collectionName, [Map args]) {
   if(_idPrefix == null) {
     throw new StateError("Subscriber can not be used before the Future"
         " returned by 'init' method has completed.");
   }
   String author = _subscriptionIdGenerator.next();
   var subscription = _createSubscription(collectionName, _connection, author,
     _dataIdGenerator, args);
   return subscription;
 }
}