Calling SignalR Hub method from client locks Xamarin android App - xamarin.android

Question

I finally got a SignalR Hub to work using the Microsoft.AspNet.SignalR vice the Microsoft.AspNetCore.SignalR, I was unable to get the Microsoft.AspNetCore.SignalR, no idea why. But I did get the other one to work. I am able to connect, link clients to connection id's using OnConnect and removing them using OnDisconnect. My Hub code is:
using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Web;
using Microsoft.AspNet.SignalR;
using SignalrHub;
namespace SignalRChat
{
public class ChatHub : Hub
{
private static readonly List<User> Users = new List<User>();
public override Task OnConnected()
{
// string userName = Context.User.Identity.Name;
string userName = Context.QueryString["username"];
string org= Context.QueryString["organization"];
string dept = Context.QueryString["dept"];
string team = Context.QueryString["team"];
string firstname = Context.QueryString["firstname"];
string lastname = Context.QueryString["lastname"];
string connectionId = this.Context.ConnectionId;
// for now I just capture username and connection Id
var user = new User();
user.Name = userName;
user.ConnectionIds = connectionId;
try
{
Users.Add(user);
}
catch (Exception ex)
{
var msg = ex.Message;
}
// TODO: Broadcast the connected user
// send list of connected users to client
Send("Welcome " + userName, "Connected users are:");
foreach (var display in Users)
{
Send("",display.Name.ToString());
}
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);
Users.Remove(item);
return base.OnDisconnected(true);
}
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;
}
}
}
Everything works fine except when I call GetConnectedUsers(), when I call that from the client with this code ConnecteduserList = client.ConnectedUsers(); the app locks up, eg; the hub never returns from that method. Clearly I'm missing something. Can anyone tell me what?
The client code in the app is:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using System.Threading.Tasks;
using Microsoft.AspNet.SignalR.Client;
namespace ChatClient.Shared
{
class Client
{
//public string username;
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://MyApp.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 List<string> ConnectedUsers()
{
List<string> Users = new List<string>();
// Locks up when this line is esecuted. The server log has nothing in it.
Users = _proxy.Invoke<List<string>>("GetConnectedUsers").Result;
return Users;
}
public Task Send(string message)
{
return _proxy.Invoke("Send", _platform, message);
}
}
}

Answer 1

Thanks to David Fowler over at GitHub who provided the link to this document (https://github.com/davidfowl/AspNetCoreDiagnosticScenarios/blob/master/AsyncGuidance.md#avoid-using-taskresult-and-taskwait), I was able to get this to work by changing my code as follows:
On the client:
From:
public List<string> ConnectedUsers()
{
// Hangs on this line
List<string> Users = _proxy.Invoke<List<string>>("getConnectedUsers").Result;
return Users;
}
To:
public async Task <List<string>> ConnectedUsers()
{
List<string> Users = await _proxy.Invoke<List<string>>("getConnectedUsers");
return Users;
}
The call to the ConnectedUsers function in Client.cs was changed as well:
From:
List<string> userList = client.ConnectedUsers();
To:
List<string> userList = await client.ConnectedUsers();
No changes to the hub code were necessary.