SignalR - sending push notification to a specific user - signalr

Question

I'm working on a PoC for a notification engine. I'm able to successfully connect and call Hub functions from JS, but I can't seem to get push notifications to work. I'm getting an Object reference not set to an instance of an object error.
Triggering class
// I was able to confirm that the connectionIds are valid
public void HandleEvent(NewNotificationEvent eventMessage)
{
// _connections handles connectionids of a user
// multiple connection ids to handle multiple open tabs
var connectionIds = _connections.GetConnectionsByUser(eventMessage.Notification.UserId);
foreach(var connectionId in connectionIds)
{
// a client is returned, but aside from the connectionid, all the properties are either null or empty
var client = _notificationHub.Clients.Client(connectionId);
///// ERROR HAPPENS HERE
///// I'm guessing NewNotification() isn't defined somewhere, but I don't know where.
client.NewNotification("Hello");
}
}
View.cshtml
var notificationHub = $.connection.NotificationHub;
$.connection.hub.qs="userId=#userId"
// Initialization
$.connection.hub.start().done(function () {
// get count unread notification count
notificationHub.invoke("unReadNotificationsCount")
.done((unreadCount) => {
if (unreadCount > 0) {
$('#notificationBadge').html(unreadCount);
hasNewNotification = true;
}
console.log('SignalR connected!');
})
.fail((data) => {
console.log('Unable to reach server');
console.log(data);
})
.always(() => $('#dropdownNotificationOptions').show());
});
// also tried notificationHub.NewNotification()
notificationHub.client.NewNotification = function (notification) {
console.log(notification);
}
NotificationHub.cs
[HubName("NotificationHub")]
public class NotificationHub : Hub
{
//ctor
public override Task OnConnected()
{
var userId = Context.QueryString["userid"];
if(userId.IsNotNullOrEmpty())
_connections.Add(Context.ConnectionId, Guid.Parse(userId));
else
_connections.Add(Context.ConnectionId, Guid.NewGuid());
return base.OnConnected();
}
public override Task OnDisconnected(bool stopCalled = true)
{
_connections.Remove(Context.ConnectionId);
return base.OnDisconnected(stopCalled);
}
public override Task OnReconnected()
{
Guid userId;
if (Guid.TryParse(Context.QueryString["userid"],out userId))
{
//var userId = _workContext.CurrentUser.Id;
var userConnection = _connections.GetUserByConnection(Context.ConnectionId);
if (userConnection == null || userConnection.IsNotNullOrEmpty())
{
_connections.Add(Context.ConnectionId, userId);
}
}
return base.OnReconnected();
}
}

Answer 1

You should have your NewNotification before the $.connection.hub.start() such as:
var notificationHub = $.connection.NotificationHub;
$.connection.hub.qs="userId=#userId"
// Moved to define before the connection start
notificationHub.client.NewNotification = function (notification) {
console.log(notification);
}
// Initialization
$.connection.hub.start().done(function () {
// get count unread notification count
notificationHub.invoke("unReadNotificationsCount")
.done((unreadCount) => {
if (unreadCount > 0) {
$('#notificationBadge').html(unreadCount);
hasNewNotification = true;
}
console.log('SignalR connected!');
})
.fail((data) => {
console.log('Unable to reach server');
console.log(data);
})
.always(() => $('#dropdownNotificationOptions').show());
});