Basically, I couldn't find any valuable resources on the internet that would help me solve the issue (except an article from Sourab Kumar — https://itnext.io/react-native-background-location-tracking-without-timeout-and-with-app-killed-3dbfbc80ad01). He presented a solution for android. I'd like to sum it up a bit and add a solution for requesting permissions and tracking users on iOS. So let's begin!
1. Requesting permissions
In order to get the user's permission, we have to request it. Fortunately, OS creators did a pretty good job in designing the API for us. So let's start!
Personally, I don't think that it is a good practice to use packages build-in functions for requesting permissions (i.e. react-native-location's RNLocation.requestPermission). If you find yourself using 3–4 packages that use device API, you'd be banging your head against the wall why you didn't choose a unified approach in the beginning.
My suggestion is to use react-native-permission. The way that you are able to request permission with this package is simple and unified! Of course, you still have to choose the permissions that you want to request.
For our purpose, we will have to distinguish between iOS and Android devices.
Now, let's request the permissions.
Notice, that in the example above, we've additionally checked whether we have Android API > 28. If we do, we have to check for another permission.
Perfect! Now that we have all the permissions, we can proceed to the implementation of the location sniffer! 🎉
For sniffing the location, we will use react-native-location.
2. Configure RNLocation
First of all, we have to configure our RNLocation. Actually… for iOS it is pretty simple. The only thing that you have to take care of is to check only for “significant changes”. For Android, we have multiple choices available. Please refer to docs for more of a comprehensive explanation. For our purpose, the configuration below will work 😎
3. Sniffing for a location
3.1 Sniffing for a location with iOS
With our RNLocation configured, we can start sniffing! It is pretty simple. Somewhere in the app just make sure that you have permissions (otherwise it will fail) and that you call subscribeToSignificantLocationUpdates().
Tadaaaa 🎉 Now you can sniff for location changes on iOS! Go ahead and try it out!
3.2 Sniffing for a location with Android
Here it is a bit more complex. Unfortunately, you cannot sniff for a location without the user knowing that you do that… I think that Sourab explained that quite well in his article, so go ahead and check it out! https://itnext.io/react-native-background-location-tracking-without-timeout-and-with-app-killed-3dbfbc80ad01
By the way, my final code is a bit different from his, so I'll still share it with you 😌 I do use foreground service in exactly the same way that Sourab does, but I have changed how the service is refreshed (Android shuts down your app after some time if it doesn't meet some criteria — which unfortunately differs DEVICE PER DEVICE).
4. Conclusion
The above example did work in my bachelor thesis, so I'm 100% sure that you can accomplish the same results with a bit of tweak. Unfortunately, the environment in React Native community and especially the way that devs can interact with device APIs are changing quite fast. So you will most likely have to edit something. But generally, the idea should work.
If you have any further questions you can always contact me on Twitter — https://twitter.com/JanDemel1. I will be more that happy to answer your questions!
