CODEWITHSUNDEEP
c#asp.net-mvc-4asp.net-mvc-5signalr
MOR_SNOW
MOR_SNOW

Reputation: 831

Pass a parameter value to the client

I have a button, that when clicked will/should notify the server. The server will then save a value to the database. If all went well, it should return true, otherwise return false.

I instantiate a hub in my view

var signalRhub = $.connection.hubSignalR;

Start the connection:

    $.connection.hub.start().done(function () {
        $("#submitBut").click(function () {
             signalRhub.server.cardAdded();
        });            
    });

Define the function that will be used by the server to return the boolean value:

signalRhub.client.cardAddedRes = function (isSuccess) {
     alert("From server: " + isSuccss);
}

My Hub class:

public class HubSignalR : Hub
{
    public bool isSuccess = false; <-- Will be set from controller

    public void CardAdded() 
    {
        Clients.Caller.CardAddedRes(isSuccess);  <-- Notice the isSuccess
    }
}

My problem is that the isSuccess value is coming from my controller, that interacts with the model/database. So I get the error:

Using a Hub instance not created by the HubPipeline is unsupported.

I tried using: GlobalHost.ConnectionManager.GetHubContext<HubSignalR>() but I can't make it work.

Here is the relevant code in my controller:

private HubSignalR signalR = new HubSignalR(); <-- Field variable

 [HttpPost]
 public ActionResult AttachCard(Card model, int MemberID)
 {
  var hub = GlobalHost.ConnectionManager.GetHubContext<HubSignalR>();
  ...
  //We saved to the database, so we call the client function with bool = true   
  hub.Clients.All.CardAdded(true);  <-- Actually I want to send to one client, NOT ALL
  //Something like hub.Clients.Caller.CardAdded();
  }

I'm forced to make the isSuccess field in my: HubSignalR class, since I need to return that as the parameter from my controller. But when the button is clicked, this value has not yet been set (I think).

I can see from the debugger, that I do reach: signalRhub.server.cardAdded(); But the server never responds, so I don't reach this function:

    signalRhub.client.cardAddedRes = function (isSuccess) {
     alert("From server: " + isSuccss);
}

I don't really get to call the CardAdded() method from my controller, cus of the GlobalHost.ConnectionManager.GetHubContext. But you can see

If you got a nicer solution than what I'm trying to do, please tell. I'm total new with SignalR and fairly new with ASP.net MVC

Upvotes: 0

Views: 953

Answers (1)

Maxim Zabolotskikh
Maxim Zabolotskikh

Reputation: 3387

Hope I got the problem right: you want to set isSuccess in controller and send it to specific client, but don't reach specific client from outside the hub?

As to "how":

You should find a way to identify your client, i.e. implement some kind of authentication. More on this here: Authentication in .net core When clients connect to SignalR, they get a connection ID. You can map the connection ID to real client identity. More info here: Mapping clients to connections

Than in you server method:

  • Get authenticated client identity
  • Get signalR hub context
  • Map client identity to existing signalR connection ID
  • Send message to that signalR connection

As I can see from you code you might be working on some personal-use/exploratory project and probably not interested in implementing authentication/don't care about security. You could get signalR connection ID in your client after connecting through $.connection.hub.id. Than you could send this ID to the server method as parameter or header. This is by no way should be used in production environment, as you would trust the client who he is, and pass parameters that are not strictly needed by your method.

As to "why":

In fact I don't think you need signalR for your use case. You call a server method, it saves to DB and returns you OK or not OK, client is happy. No need to pass it through signalR.

You do need signalR e.g. when: - Same client is logged in on several devices and wants to get updates if changes were made on one of them - Client works on something and another one changes same data. You want to inform the first client. - Inform your client of an event that was not triggered by him (new notification)

In all this cases you have some kind of authentication and sending signalR message to the right client is not a problem.

Answer to comment below

I have little experience with ajax, i guess it might work. Another idea, if you want to avoid authentication, is a subscription model with SignalR. You have to find out which specific resources you have, let's say "game" in your case, which have IDs. Than clients, interested in that particular resource, shall subscribe to changes.

All participants of a particular card game instance shall call a hub method defined like this:

public async Task SubscribeToGameChanges(long id)
{
    await this.Groups.AddToGroupAsync(this.Context.ConnectionId, Helper.GetGameGroupName(id));
}

public static class Helper { public static string GetGameGroupName(long id) { return $"Game_{id}"; } }

Than call it from client. Note the AddToGroupAsync. SignalR shall create a group with given name and add a client to it. If group exists, it will just add another client. So you have a group per game instance with a list of interested clients (players).

Now when a change happens to the game, you notify all your clients by calling from your controller on hub context:

await hubContext.Clients.Groups(Helper.GetGameGroupName(id)).SendAsync("myNotifyMethod", myParameters);

You could pack all your changes into parameters, or just inform the clients that the state of the game (or whatever other resource) has changed and clients shall requery the state through normal API call.

Also I noticed you use GlobalHost in your code. My code samples are for .net core SignalR version and might slightly differ in your case. See here on differences between .net core and full .net SignalR.

Upvotes: 1

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