目标C IOS 11中的静默通知显示横幅出错

我在IOS 11的目标C代码中实现了无声通知。通过添加此方法使用FCM通知。 What is Silent Push Notification? When does the device receive it?

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult result))handler
{

   //Success
    handler(UIBackgroundFetchResultNewData);
}

Paylod是:

    {
    "aps" = {
        "content-available" : 1,
        "sound" : ""
    };
    // You can add custom key-value pair here...
}

didReceiveRemoteNotification 当收到通知时调用方法,但我的问题是,当接收到无提示通知时,为什么横幅可见。如何限制通知横幅。