Firebase推进没有显示在横幅，当在背景中时

Question

我使用firebase向我的应用发送推送通知。我使用警报视图来显示从firebase收到的消息，它工作正常，但在后台，通知横幅不会出现在通知中，但正确调用didreceiveremotenotifications方法。无法找出问题所在。请建议

func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject])
{
    if isBackground == false
    {
        let notifiAlert = UIAlertView()
        let NotificationMessage : AnyObject? =  userInfo["alert"]
        notifiAlert.title = userInfo["title"] as! String
        notifiAlert.message = NotificationMessage as? String
        notifiAlert.addButtonWithTitle("OK")
        notifiAlert.show()
    }
    else
    {
        print(userInfo)
          NSNotificationCenter.defaultCenter().postNotificationName("pushReceived", object: userInfo)
    }
}

在上面的背景中，用户信息打印如下

[title: Check your billing details, notification: 
{
   body = test;
   e = 1;
   title = "test notification";
}, collapse_key: com.softence.viabill, 
url: http://softence.com/devTest/viabill-sample-app/main.html?, 
    message: Please check the latest generated bill, from: 314848715780]