来自Azure通知中心的Null参考异常

Question

I have been using Azure Notification Hubs along with GCM to send notifications to the users of my app. This was all working great until I published the app to the Play Store. Now it gives a 500 Server error whenever I try to post a notification. I have no idea why this error is happening. Perhaps the app is not picking up the RavenDB where the notifications are stored? But it looks more like the service is not getting back users that are registered on the Hub. I really don't know... Any help would be so appreciated!

This is my stacktrace when run locally, it is the same but less detailed when published:

"Message": "An error has occurred.",
"ExceptionMessage": "Value cannot be null.\r\nParameter name: source",
"ExceptionType": "System.ArgumentNullException",
"StackTrace": "   at System.Linq.Enumerable.Where[TSource](IEnumerable`1 source, Func`2 predicate)\r\n   
at AcademicAssistantService.Controllers.NotificationController.<GetRecipientNamesFromNotificationHub>d__8.MoveNext() 
in C:\\Users\\Kenneth\\Documents\\College\\Semester 8\\AcademicAssistantService\\AcademicAssistantService\\Controllers\\NotificationController.cs:line 105

This is the Controller action:

// POST api/notification
public async Task<IHttpActionResult> Post([FromBody]Notification notification, String key)
{
    var notificationToSave = new Notification
    {
        NotificationGuid = Guid.NewGuid().ToString(),
        TimeStamp = DateTime.UtcNow,
        Message = notification.Message,
        SenderName = notification.SenderName
    };

    var recipientNames = await GetRecipientNamesFromNotificationHub(key);

    var recipientNamesString = CreateCustomRecipientNamesString(recipientNames);

    string notificationJsonPayload =
        "{\"data\" : " +
        "   {" +
        "   \"message\": \"" + notificationToSave.Message + "\"," +
        "   \"senderName\": \"" + notificationToSave.SenderName + "\"," +
        "   \"recipientNames\": \"" + recipientNamesString + "\"" +
        "   }" +
        "}";


    if (key == null)
    {
        var result = await _hubClient.SendGcmNativeNotificationAsync(notificationJsonPayload);

        notificationToSave.TrackingId = result.TrackingId;
        notificationToSave.Recipients = recipientNames;
    }
    else
    {
        foreach (string r in recipientNames)
        {
            if ((r != notification.SenderName))
            { 
                var result = await _hubClient.SendGcmNativeNotificationAsync(notificationJsonPayload, "user:" + r);
                notificationToSave.TrackingId = result.TrackingId;
                notificationToSave.Recipients = recipientNames;
            }
        }
    }

    await Session.StoreAsync(notificationToSave);

    return Ok(notificationToSave);
}

To get names from hub:

public async Task<List<string>> GetRecipientNamesFromNotificationHub(String key)
{
    var registrationDescriptions = await _hubClient.GetAllRegistrationsAsync(Int32.MaxValue);

    var recipientNames = new List<String>();
    foreach (var registration in registrationDescriptions)
    {
        if (registration is GcmRegistrationDescription)
        {
            var userName = registration.Tags
                                           .Where(t => t.StartsWith("user"))
                                           .Select(t => t.Split(':')[1].Replace("_", " "))
                                           .FirstOrDefault();
            userName = userName ?? "Unknown User";

            Conversation convo = db.Conversations.Find(key);

            foreach (User u in convo.Users)
            {
                if (u.Email == userName && !recipientNames.Contains(userName))
                {
                    recipientNames.Add(userName);
                }
            }
        }
    }
    return recipientNames;
}

Answer 1

Could you use Service Bus Explorer and verify indeed you have tags starts with "user". And I also see you are using GetAllRegistrationsAsync API, which is recommend to use only for debugging purpose. This is heavily throttled API.

Thanks, Sateesh