The low reliability of GCM on Android is such that I have moved to another service to handle push messages: Pushy, (https://pushy.me/)
The service relies on MQTT, and from my experience as well as many other reviews, the real time feature-set holds up to its name and rarely does a message get dropped. However, contacting support, they noted that there is no iOS integration and only support Android.
I have searched widely but have not found a suitable replacement for iOS that supports MQTT out of the box.
Is there such a service available to allow for more dependable push messages?
The problem is iOS's limitations on background services makes staying connected to a MQTT broker difficult.
Apple have a list of use cases that are allowed to run in the background, the list can be found in this document
If your app does not conform to this list it is likely to not get approved for the App Store.
来源：https://stackoverflow.com/questions/36522224/mqtt-service-for-ios-push-notifications