How does CLVisit work?

Question

I am working on a app that relies heavily on monitoring user visits in possibly multiple regions / areas. I am currently experimenting with region monitoring which works pretty well, however, the location callback is not as accurate as I want it to be. I have seen CLVisit, but the documentation out there doesnt explain it very well, especially its use.

Answer 1

I think you are misunderstanding the concept of CLVisits. There is actually no Visit object that you need to create. The CLLocationManager delegate method is triggered by the algorithm that apple has determined (see wwdc lecture for more info). This is explained in the CLLocationManager documentation...

Getting the Visited Locations

In iOS, the visits service provides an alternative to the significant location change service for apps that need location information about interesting places that the user visited. For example, if the user is in one location for an extended period of time, the service might generate an event when the user arrives at that location and another when the user leaves that location. The service is intended for apps that might already be using the significant location change service and want an even lower power way to do so. You would not use this service to create navigation apps or apps that rely on regular location updates.

To begin the delivery of visit-related events, assign a delegate to the location manager object and call its startMonitoringVisits method. As the location manager generates visit events, it delivers that information to its delegate’s locationManager:didVisit: method. The event data delivered to your delegate includes only the information that occurred after you started the delivery of events. In other words, if you start the delivery of events after the user arrived at an interesting location, the event delivered by the system when the user departed that location would not reflect the actual arrival time. If the system terminates your app, this service relaunches it when new visit events are ready to be delivered.

That said if you look at this article from NSHipster, it references some current issues with CLVists (for iOS 8.1). It essentially goes on to say that if you want infrastructure that extremely precise don't use CLVisit. Seems like you're doing it right (for now at least).

CLVisit is, as of iOS 8.1, not all that precise. While start and end times are generally accurate within a minute or two, lines get blurred at the edges of what is and what is not a visit. Ducking into a corner coffee shop for a minute might not trigger a visit, but waiting at a particularly long traffic light might. It’s likely that Apple will improve the quality of visit detection in future OS upgrades, but for now you might want to hold off on relying on CLVisit in favor of your own visit detection for use cases where it’s vital your data is as accurate as it can be.