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<Dictionary<string, object>> message

public class MyHub : Hub
{
    public Task SendMessage(List<Dictionary<string, object>> 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<Dictionary<string, object>> Items { get; set; }

   public List<string> 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!

Answer 1

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>(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<T>() to convert a json string you recieve from the client into a Object.

Answer 2

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

1. 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;
       }
   }
   

2. 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<string, object> {
           { "T1", new { Name = "TT1" } },
           { "T2", new { Name = "TT2" } },
           { "T3", new { Name = "TT3" } },
       };
       var item2 = new Dictionary<string, object> {
           { "T11", new { Name = "TT11" } },
           { "T12", new { Name = "TT12" } },
           { "T13", new { Name = "TT13" } },
       };
   
       await hubConnection.SendAsync("SendMessage", new Message {
           MessageId = 1,
           Items = new List<Dictionary<string, object>> {
               item1,
               item2
           },
           TextMessages = new List<string> {
               "H1",
               "H2"
           }
       });
       var on = hubConnection.On("ReceiveMessage", OnReceivedAction);
       Console.WriteLine($"Client is Start");
       Console.ReadLine();
       on.Dispose();
       await hubConnection.StopAsync();
   }