从任何Xamarin（Visual Studio 2017）android活动向MessageR集线器发送消息

Question

I've been able to create and receive messages from a SignalR hub from a html page, aspx page and an Xamarin client which is the app I really need it for using Microsoft.AspNet.SignalR.Client v2.4.1 using Xamarin in Visual Studio 2017. Once my Xamarin app authenticates the user I start the connection to the hub, next I wire up an event to receive messages. All of this works just fine and I can receive messages in the android app no matter what activity is the current activity thanks to the event that is wired up. Now that I have this working I want to be able to send a message from the client to the hub without creating another connection to the hub. I've looked at static classes, but cannot get that to work. My code is:

This is the code that is executed after the user is authenticated:

// Start SignalR connection
Client client = new Client(MyUser.Firstname + " " + MyUser.Lastname, MyUser.Username);

await client.Connect();

// Wire up the message received event
client.OnMessageReceived += (sender2, message) => RunOnUiThread(() => showMessage(message));

From here the user can navigate from view to view and is able to receive messages from the hub via the event and the showMessage method. This all works flawlessly.

My Client Code: This code was copied from a stack overflow working example, I modified it to my requirements.

namespace ChatClient.Shared
{
    class Client
    {
        private readonly string _platform;
        private readonly HubConnection _connection;
        private readonly IHubProxy _proxy;

        public event EventHandler<string> OnMessageReceived;

        public Client(string platform, string username)
        {
            string _username = "username=" + username;
            _platform = platform;
            _connection = new HubConnection("https://Example.com/SignalRhub", _username);
            _proxy = _connection.CreateHubProxy("chathub");
        }

        public async Task Connect()
        {

            await _connection.Start();                 _proxy.On("broadcastMessage", (string platform, string message) =>
            {
                if (OnMessageReceived != null)
                    OnMessageReceived(this, string.Format("{0}: {1}", platform, message));
            });

            Send("Connected");
        }

        public async Task<List<string>> ConnectedUsers()
        {

            List<string> Users = await _proxy.Invoke<List<string>>("getConnectedUsers");

            return Users;
        }

        public Task Send(string message)
        {
            return _proxy.Invoke("Send", _platform, message);
        }
    }
}

Now what I need to do is send a message to the hub using the connection created just after the logon to be distributed to all connected users. I cannot figure out how to do that, I've tried using a static class and attempted to use methods I've found on the web, but nothing seems to work.

My Hub code:

public class ChatHub : Hub
{

    private static readonly List<User> Users = new List<User>();

    public override Task OnConnected()
    {

        string userName = Context.QueryString["username"];
        string firstname = Context.QueryString["firstname"];
        string lastname = Context.QueryString["lastname"];
        string connectionId = this.Context.ConnectionId;

        var user = new User();
        user.Name = userName;
        user.ConnectionIds = connectionId;


        try
        {
            Users.Add(user);
        }
        catch (Exception ex)
        {
            var msg = ex.Message;
        }

        // send list of connected users to client as a test
        Send("Welcome " + userName, "Connected users are:");

        foreach (var display in Users)
        {
            Send("",display.Name.ToString());

        }

        // test sending to a specific user
        SendOne(connectionId, userName, "This is to a specific user.");

        return base.OnConnected();
    }

    public override Task OnDisconnected(bool stopped)
    {

        string userName = Context.User.Identity.Name;
        string connectionId = Context.ConnectionId;

        var item = Users.Find(x => x.ConnectionIds == connectionId);

        Send(item.Name , " disconnected.");

        Users.Remove(item);


        return base.OnDisconnected(true);
    }

    public void SendOne(string connectionId, string userName, string message)
    {

        Clients.Client(connectionId).broadcastMessage(userName, message);

    }

    public void Send(string name, string message)
    {
        // Call the broadcastMessage method to update clients.
        Clients.All.broadcastMessage(name, message);
    }

    public List<string> getConnectedUsers()
    {
        List<string> UserNames = new List<string>();

        foreach (var ConnectedUser in Users)
        {
            UserNames.Add(ConnectedUser.Name );
        }
       return UserNames;
    }
}

There are a lot of other things I will be doing in the hub, but for now I need to get the client to send messages without creating another connection

Is there a way I can access the connection created after the user is authenticated in other views/activities?

* Update *

I changed my code in accordance with Leo Zhu's answer below, however I get an error when I try to instantiate the class on the line:

Client client = new Client.GetInstance(MyUser.Firstname + " " + MyUser.Lastname, MyUser.Username);

GetInstance does not exist when it actually does. No idea why it isn't "found".

* Update *

Removed the new keyword from the line:

Client client = new Client.GetInstance(MyUser.Firstname + " " + MyUser.Lastname, MyUser.Username);

It now reads:

Client client = Client.GetInstance(MyUser.Firstname + " " + MyUser.Lastname, MyUser.Username);

Works like a charm.

Answer 1

Or you can try the singleton pattern,for example (Just to provide ideas，you need to code to your own needs):

public sealed class Client
  {
    // A private constructor to restrict the object creation from outside
    private Client()
     {
      ...
     }
    // A private static instance of the same class
    private static Client instance = null;
    public static Client GetInstance()
      {
       // create the instance only if the instance is null
       if (instance == null)
         {
           instance = new Client();
         }
       // Otherwise return the already existing instance
      return instance;
      }

  }

then you could call by Client.GetInstance();