Is there a way to put code in iOS that is always watching in the background for the contact store to change? If I put it in my app, then the user can close the app, and the app won't receive notifications when the contact store changes? Is there an app extension I can use that would allow me to do this, whether that is the intent of the extension or not?
How do I run code in the background in iOS that will always run?
Look at BackgroundTasks Framework
, hope that will meet your needs.
Some details here
https://www.raywenderlich.com/21242372-background-tasks-in-ios/lessons/1
or
https://www.spaceotechnologies.com/ios-background-task-framework-app-update/