Android app did not receive data from SignalR hub

Question

I already read these topics:
how to use SignalR in Android
Android Client doesn't get data but .net client getting data from SignalR server

I write a simple chat system with Android that works with SignalR.
It is supposed to the clients send messages (by calling SendMessage method on the server) and the server should call the NewMessage method on the clients.

Here is my ChatHub class (simplified) written in C#.

public class ChatHub : Hub
{
    // Store the clients connections Id
    static readonly List<string> _connectedClients;

    public override Task OnConnected()
    {
        // Keep connections id
        // This section works fine and when the android device connects to the server,
        // Its connection id will stored.
        _connectedClients.Add(Context.ConnectionId)

        //... other codes
    }

    public void SendMessage(string message)
    {
        foreach (var connectionId in _connectedClients)
        {
            // according to the logs 
            // android device connection id exists here
            // and it works fine.
            Clients.Client(connectionId).NewMessage(message);
        }
    }
}

When the android client connects to the server, On the OnConnected method, the connection id will be stored in the _connectedClients and it works fine.

In the SendMessage method of the ChatHub class, We have the android device connection id, and I'm sure that the android device is within the list

And here is my Andoird codes:

public class ChatActivity extends AppCompatActivity
{
    // private fields
    HubConnection connection;
    HubProxy hub;
    ClientTransport transport;

    protected void onCreate(Bundle savedInstanceState) {

        Logger logger = new Logger() {
            @Override
            public void log(String message, LogLevel logLevel) {
                Log.e("SignalR", message);
            }
        };

        Platform.loadPlatformComponent(new AndroidPlatformComponent());
        connection = new HubConnection("192.168.1.100");
        hub = connection.createHubProxy("chatHub"); // case insensitivity

        transport = new LongPollingTransport(connection.getLogger());

        // no difference when using this:
        //transport = new ServerSentEventsTransport(connection.getLogger());

        // this event never fired!
        hub.subscribe(new Object() {
            public void NewMessage(String message)
            {
                Log.d("<Debug", "new message received in subscribe"); // won't work!
            }
        }

        // this event never fired!
        hub.on("NewMessage", new SubscriptionHandler() {
            @Override
            public void run() {
                Log.d("<Debug", "new message received in `on`"); // won't work!
            }
        });

        // connect to the server that works fine.
        SignalRFuture<Void> awaitConnection = connection.start(transport);
        try {
            awaitConnection.get(); // seems useless when using this or not!
        }
        catch (Exception ex) {
        }

        // this method works fine.
        hub.invoke("sendMessage", "this is a test message to the server")
        .done(new Action<Void>() {
                @Override
                public void run(Void aVoid) throws Exception {
                    Log.d("<Debug", "message sent."); // Works fine
                }
        });

    }
}

In the above java code, invoking the sendMessage on the server works fine and the server get the messages.
But the only problem is that the hub.on(...) or hub.subscribe(...) events are never be called by the server.
In a simple description, My app can send message, but can not receive message from the others.
Any suggestion will be appreciated.

Answer 1

You does not provider parameters in your client-side which should be same as your side-site. The code should be below:

      hub.on("NewMessage", new SubscriptionHandler1<String>() {
        @Override
        public void run(String message) {
            Log.d("<Debug", "new message received in `on`"); 
        }
    },String.class);  //do not forget say the String class in the end

Answer 2

For the futures this is the way I finally achieved the answer (please first read the question android codes):

public class ChatActivity extends AppCompatActivity
{
    // private fields
    HubConnection connection;
    HubProxy hub;
    ClientTransport transport;

    protected void onCreate(Bundle savedInstanceState) {

        Logger logger = new Logger() {
            @Override
            public void log(String message, LogLevel logLevel) {
                Log.e("SignalR", message);
            }
        };

        Platform.loadPlatformComponent(new AndroidPlatformComponent());
        connection = new HubConnection("192.168.1.100");
        hub = connection.createHubProxy("chatHub"); // case insensitivity

        /* ****new codes here**** */
        hub.subscribe(this);

        transport = new LongPollingTransport(connection.getLogger());

        /* ****new codes here**** */
        connection.start(transport);

        /* ****new codes here**** */
        /* ****seems useless but should be here!**** */
        hub.subscribe(new Object() {
            @SuppressWarnings("unused")
            public void newMessage(final String message, final String messageId, final String chatId,
                                   final String senderUserId, final String fileUrl, final String replyToMessageId) {


            }
        });


        /* ********************** */
        /* ****new codes here**** */
        /* **** the main method that I fetch data from server**** */
        connection.received(new MessageReceivedHandler() {
            @Override
            public void onMessageReceived(final JsonElement json) {
                runOnUiThread(new Runnable() {
                    public void run() {
                        JsonObject jsonObject = json.getAsJsonObject();
                        Log.e("<Debug>", "response = " + jsonObject.toString());

                    }
                });
            }
        });
        /* ********************** */

    }
}

!important note:
The priority of the codes is important. this is how I fix my problem in this topic.