applicationWillResignActive impact on application?

I am writing an application that records a users position at regular intervals whilst walking. I am using an NSTimers to schedule "startUpdatingLocation" followed by calling "stopUpdatingLocation" shortly afterwards to save as much battery as possible.

I 开发者_运维知识库want the user to be able to start the application and lock the phone thereby putting the application in an inactive state. My question is when this happens my application (when running via Xcode) seems to continue as normal, but I am curious if there are any differences in the way the application runs in this state as apposed to when the application is running as active?

From the docs it only mentions "applicationWillResignActive" with regards to the application passing through that state on its way to the background. I am more interested in how an application behaves when a used locks the UI and puts the phone away, I just want to make sure its going to keep doing what it should be doing or do I need to take extra measures?

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When you app hits applicationWillResignActive it can continue to receive location updates if you use the UIBackgroundModes option in your apps info.plist.

Add the location key.

It is important that you do not use a timer in the background as timers will run but hold their "fire" until the app becomes active again. Thus you will only get one read when the user comes back to the app. The GPS location accuracy level is what will drive how much the battery is affected.

In your app description in the App Store, Apples requires:

Continued use of GPS running in the background can dramatically decrease battery life.

You app will not be allowed to go live until the above text is in the description for the user to read.

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You should definitely be testing this on a device. The simulator doesn't auto-lock, for instance.

applicationWillResignActive is called when the user presses the home button, when another app fires a notification the user accepts (including when a call comes in), and when the device locks.

Look into the multitasking documentation, and what it has to say about background location updates.

My suggestion is that you conserve the user's battery by: - starting a timer, which when fired, starts location updates (and stops the timer) - when you get an adequately-accurate position record, stop location updates and restart the timer - if location updates fail, restart the timer for a longer period. Maybe they're underground.

The most efficient approach is using significant location update service while your application is in the background or the screen is locked on your app. You might get one update every ten minutes or so.

Remember also, the user can disable your app's location services permissions. Especially these days...