derrrrrp.cs

var registrationId = string.Empty;
var allRegistrations = await hubClient.GetAllRegistrationsAsync(10);

foreach (var registration in allRegistrations)
{
    switch (deviceType)
    {
        case NotificationSubscriptionV1.DeviceTypes.Android:
        {
            var reg = registration as GcmRegistrationDescription;
            if (reg != null)
            {
                if (reg.GcmRegistrationId.Equals(id))
                    registrationId = reg.RegistrationId;
            }
        }
        break;
        case NotificationSubscriptionV1.DeviceTypes.iOS:
        {
            var reg = registration as AppleRegistrationDescription;
            if (reg != null)
            {
                if (reg.DeviceToken.Equals(id))
                    registrationId = reg.RegistrationId;
            }
        }
        break;
        case NotificationSubscriptionV1.DeviceTypes.Windows:
        {
            var reg = registration as WindowsRegistrationDescription;
            if (reg != null)
            {
                if (reg.ChannelUri.ToString().Equals(id))
                    registrationId = reg.RegistrationId;
            }
        }
        break;
        case NotificationSubscriptionV1.DeviceTypes.WindowsPhone:
        {
            var reg = registration as MpnsRegistrationDescription;
            if (reg != null)
            {
                if (reg.ChannelUri.ToString().Equals(id))
                    registrationId = reg.RegistrationId;
            }
        }
        break;
    }
}