CODEWITHSUNDEEP
dartangular-dart
MajorRefactoring
MajorRefactoring

Reputation: 3753

Rebinding a page in AngularDart when the data is loaded via SignalR

I've got an AngularDart application that is working, but I feel like I'm doing it wrong...

The application shows a list of events as they are received. The events get to the app via SignalR, but I don't think that's really relevant - the issue is the way I'm having to update the component's state in order to see the changes in the state get displayed on the page.

Here is a cut down version of my component:

@Component( selector: 'liveEvents', templateUrl: 'live_events.html', useShadowDom: false )
class LiveEvents implements ScopeAware {
    VmTurnZone _vmTurnZone;
    EventReceiver _eventReceiver;
    LiveEvents( this._vmTurnZone, this._eventReceiver );
    List<Event> events = new List<Event>();
    void _onEventReceived(Event event) {
        //TODO: This just does not seem right...
        _vmTurnZone.run(() => events.add(event));
    }

    void set scope(Scope scope) {
        var _events = _eventReceiver.subscribeToAllEvents( "localhost", _onEventReceived );
    }
}

The EventReceiver class is responsible for connecting to a SignalR server, receiving messages from that server and converting them into Event objects, and then calling whatever function was specified in the subscribeToAllEvents (in this case, _onEventReceived)

The angular template html is very simple:

<ul>
    <li ng-repeat="event in events">Event: {{event.Id}}</li>
</ul>

This all works fine, but the bit I don't like is having to inject a VmTurnZone object into the component, and to have to update the events property from within a call to run on that VmTurnZone. It just seems a bit overly complicated to me. But if I DON'T do it in the VmTurnZone.run method, when the events property gets updated, the view is not updated to reflect that change. Only from within VmTurnZone.run does it work.

Is there a simpler way to do what I'm after here? I've looked at adding a watch to the scope, but that didn't seem to work (and looks to me like it should be used for changes that happen the other way around - ie, the view updates the scope, and you want to do something when that happens).

Can any AngularDart experts let me know if there's a better way to do what I'm after?

Upvotes: 2

Views: 323

Answers (2)

Jake Rote
Jake Rote

Reputation: 2247

https://api.dartlang.org/apidocs/channels/stable/dartdoc-viewer/dart:async.Stream

You could add your events to stream and then listen for these and signalr will see these changes, for example:

@Component( selector: 'liveEvents', templateUrl: 'live_events.html', useShadowDom: false )
class LiveEvents implements ScopeAware {
    EventReceiver _eventReceiver;
    LiveEvents( this._eventReceiver );
    List<Event> events = new List<Event>();

    void set scope(Scope scope) {
        subscribe().listen((event){
            events.add(event);
        });
    }

    Stream<Event> subscribe(){
        var streamController = new StreamController<Event>();

        _eventReceiver.subscribeToAllEvents( "localhost", (event){
            streamController.add(event);
        });

        return streamController.stream;
    }
}

Upvotes: 1

G&#252;nter Z&#246;chbauer
G&#252;nter Z&#246;chbauer

Reputation: 657466

As far as I know this is necessary when the source of the change is outside of the default Angular zone (for example some JavaScript library) for Angular to recognize model changes.

Upvotes: 0

Related Questions