public override async Task OnDisconnectedAsync(Exception exception)
{
string name = Context.User.Identity.Name;
ConnectionMapping <string> .Remove(name, Context.ConnectionId);
await base.OnDisconnectedAsync(exception);
}
public override async Task OnConnectedAsync()
{
string name = Context.User.Identity.Name;
ConnectionMapping <string> .Add(name, Context.ConnectionId);
await base.OnConnectedAsync();
}