ASP.NET Core 2 SignalR Hub to receive complex object instead of string

Question

I'm currently working on a ASP.NET Core 2 application using SignalR Core. I was wondering if it is possible to receive a complex object within the Hub class instead of a simple string or simple data structure.

Works - This example works fine: string message

public class MyHub : Hub
{
    public Task SendMessage(string message)
    {
        // ... some logic
    }
}

Works - This example works fine as well: List> message

public class MyHub : Hub
{
    public Task SendMessage(List> message)
    {
        // ... some logic
    }
}

Doesn't work correctly - It seems I cannot transfer complex objects via SignalR e.g. if I create a custom message class:

public class Message 
{
   public int MessageId { get; set; }

   public List> Items { get; set; }

   public List TextMessages { get; set; }
}

public class MyHub : Hub
{
    public Task SendMessage(Message message)
    {
        // ... some logic
    }
}

Do you know how to transfer complex objects via a SignalR RPC?

Thank you!

user_8458043 · Answer

You can use the Newtonsoft.Json Nuget.

There you have a JsonConverter that can serializ your object.

So in your example:

    public class MyHub : Hub
    {
          public Task SendMessage(Message message)
          {
             var messageJsonString = JsonConvert.SerializeObject(message);
             // some logic
           }
    }

And on your client you can convert it back to an object. It´s have a nativ API so you just call

connection.on("ReceiveMessage",  (message) => { 
    let messageObject = JSON.parse(message);
    // Other code here
});

Now message is again the object you send from the server.

And of course you can use JsonConvert.DeserializeObject() to convert a json string you recieve from the client into a Object.

user_6265620 · Answer

Follow steps below for a working demo which passing Message between signalR Client and Server.

Server

public class TimeHub: Hub
{
    public async Task UpdateTime(string message)
    {
        if (Clients != null)
        {
            await Clients?.All.SendAsync("ReceiveMessage", message);
        }
    }
    public Task SendMessage(Message message)
    {
        // ... some logic
        return Task.CompletedTask;
    }
}

Client

private static async void Connect()
{
    var hubConnectionBuilder = new HubConnectionBuilder();
    #region Worked
    var hubConnection = hubConnectionBuilder.WithUrl("https://localhost:44381/timeHub", options =>
    {

    }).Build();
    #endregion

    await hubConnection.StartAsync();
    await hubConnection.SendAsync("UpdateTime", $"From Client");
    var item1 = new Dictionary {
        { "T1", new { Name = "TT1" } },
        { "T2", new { Name = "TT2" } },
        { "T3", new { Name = "TT3" } },
    };
    var item2 = new Dictionary {
        { "T11", new { Name = "TT11" } },
        { "T12", new { Name = "TT12" } },
        { "T13", new { Name = "TT13" } },
    };

    await hubConnection.SendAsync("SendMessage", new Message {
        MessageId = 1,
        Items = new List> {
            item1,
            item2
        },
        TextMessages = new List {
            "H1",
            "H2"
        }
    });
    var on = hubConnection.On("ReceiveMessage", OnReceivedAction);
    Console.WriteLine($"Client is Start");
    Console.ReadLine();
    on.Dispose();
    await hubConnection.StopAsync();
}

user_249097 · Answer

If you are considering using JSON parsing just for the sake of passing multiple objects/parameters to client side, there is an alternative.

Server side (C#). You can pass any number of parameters to the anonymous object array.

SendCoreAsync("MethodName", new object[] {someObject, someNumber, someString });

Client side (Typescript)

private alertHandler = (someObject: any, someNumber: number, someString: string) => {
    console.log(someObject, someNumber, someString);
};

I have a slightly more detailed answer here

ASP.NET Core 2 SignalR Hub to receive complex object instead of string

3 Answers