Foreground notification handling (onMessage) and NotificationServiceExtension

[bumpingChris]

Hi,

In iOS, I use NotificationServiceExtension to modify the message before showing to the user. This works fine when the app is in the background. But when in the foreground, I see that the NotificationServiceExtension does get called when the message arrives, BUT the onMessage listener does not see the modified message.

How can I get onMessage to see the modified message?

Thank you for your help.

[mikehardy]

Interesting - I'm not sure, I have not considered that use case, it's literally never come up before :-)

There may not be a way owing to control flow / when things happen, and what data is provided to onMessage.

More concretely: onMessage is a hook called in our code from firebase-ios-sdk and we are just like a postal carrier, delivering the message to higher levels that we received from lower levels

There may be something you can do with regard to swizzling such that the call chain has your extension prior to the firebase-ios-sdk Messaging delegate swizzle (if I'm understanding that correctly) - but that would be experimental on your behalf, you would have to play around with it to see if a) I am even guessing in the correct area b) you even have control of the order and c) you can effectively change it to work the way you want

A separate path may be to use NSUserDefault in the extension to leave yourself a clue as to what happened then in react-native check it (via https://reactnative.dev/docs/settings) - a bit less elegant then a perfect swizzle+ordering thing but also a lot less subtle.

Maybe useful?

[bumpingChris]

@mikehardy Thank you, Mike, for your thorough answer. I was hoping, of course, that there would be an easy way to get the result from the extension, but if there isn't I could recode what the extension does in the onMessage listener. Not as elegant for sure, but much easier than experimenting with swizzling.

Thanks again.
Chris

[mikehardy]

Luckily at least NSUserDefaults is really easy to work with both in native code and react-native level, it's a good escape hatch. Good luck with your project!