How can I keep trying to subscribe to signalR from

问题:

How can I keep attempting to connect to signalR in a safe way that allows a few hundred milliseconds (at least) in between attempts until the connection is established and if so, could someone provide a better way pf dealing with the various stages of connectivity to the web-sockets?

We are using signalR on a .NET backend and I am trying to use it to display real-time push notifications in an Angular 4 UI. It works great when it connects, but there is a problem where sometimes it takes 2-3 times to connect. I also get an error this.startSignalRListener is not a function if I put it inside the catch block to try to reconnect that way.

Any suggestions would be greatly appreciated.

I am using "@aspnet/signalr-client": "^1.0.0-alpha2-final" in package.json

Here is some of my code from my service class...

import { HubConnection } from '@aspnet/signalr-client';

@Injectable()
export class RealTimeService implements OnInit {

    private hubConnection: HubConnection;

    constructor() {}

    ngOnInit() {
        this.startSignalRListener();
    }

    public onConnection(): void {
        const domain = this.state.domain;

        this.hubConnection
            .invoke('WatchSomething', [ 'abc.com' ])
            .catch(err => console.error('signalR error: ', err));

        this.hubConnection.on('some_thing', (res: any) => {
            console.log('do stuff...', res);
        });
    }

    public startSignalRListener() {
        const connection = `www.realtimeapi.com`;

        this.hubConnection = new HubConnection(connection);

        this.hubConnection
            .start()
            .then(() => {
                this.onConnection();
            })
            .catch(err => {
                console.log('Error while establishing connection...');
            });
    }
}

How can I best reconnect when a connection fails? Any suggestion would really help me out as it fails often on the first try.

回答1:

You can try to use the setTimeout function to delay your reconnects:

.catch(err => {
    console.log('Error while establishing connection... Retrying...');
    setTimeout(() => this.startSignalRListener(), 3000);
});

In this case I suggest you to move the this.hubConnection.on('domain_bid' out of startSignalRListener to bind this stuff only once.