Proper way to exit iPhone application?

Question

I am programming an iPhone app, and I need to force it to exit due to certain user actions. After cleaning up memory the app allocated, what's the appropriate method to call to terminate the application?

Answer 1

In addition to the above, good, answer I just wanted to add, think about cleaning up your memory.

After your application exits, the iPhone OS will automatically clean up anything your application left behind, so freeing all memory manually can just increase the amount of time it takes your application to exit.

Answer 2

It may be appropriate to exit an app if it is a long lived app that also executes in the background, for example to get location updates (using the location updates background capability for that).

For example, let's say the user logs out of your location based app, and pushes the app to the background using the home button. In this case your app may keep running, but it could make sense to completely exit it. It would be good for the user (releases memory and other resources that don't need to be used), and good for app stability (i.e. making sure the app is periodically restarted when possible is a safety net against memory leaks and other low memory issues).

This could (though probably shouldn't, see below :-) be achieved with something like:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    if (/* logged out */) {
        exit(0);
    } else {
       // normal handling.
    }
}

Since the app would then exit out of the background it will not look wrong to the user, and will not resemble a crash, providing the user interface is restored the next time they run the app. In other words, to the user it would not look any different to a system initiated termination of the app when the app is in the background.

Still, it would be preferable to use a more standard approach to let the system know that the app can be terminated. For example in this case, by making sure the GPS is not in use by stopping requesting location updates, including turning off show current location on a map view if present. That way the system will take care of terminating the app a few minutes (i.e. [[UIApplication sharedApplication] backgroundTimeRemaining]) after the app enters the background. This would get all the same benefits without having to use code to terminate the app.

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    if (/* logged out */) {
       // stop requesting location updates if not already done so
       // tidy up as app will soon be terminated (run a background task using beginBackgroundTaskWithExpirationHandler if needed).
    } else {
       // normal handling.
    }
}

And of course, using exit(0) would never be appropriate for the average production app that runs in the foreground, as per other answers that reference http://developer.apple.com/iphone/library/qa/qa2008/qa1561.html

Answer 3

This has gotten a good answer but decided to expand a bit:

You can't get your application accepted to AppStore without reading Apple's iOS Human Interface Guidelines well. (they retain the right to reject you for doing anything against them) The section "Don't Quit Programmatically" http://developer.apple.com/library/ios/#DOCUMENTATION/UserExperience/Conceptual/MobileHIG/UEBestPractices/UEBestPractices.html is an exact guideline in how you should treat in this case.

If you ever have a problem with Apple platform you can't easily find a solution for, consult HIG. It's possible Apple simply doesn't want you to do it and they usually (I'm not Apple so I can't guarantee always) do say so in their documentation.

Answer 4

Exit an app other way

I did this helper, though, that use no private stuff:

Exit(0);

Answer 5

Check the Q&A here: https://developer.apple.com/library/content/qa/qa1561/_index.html

Q: How do I programmatically quit my iOS application?

There is no API provided for gracefully terminating an iOS application.

In iOS, the user presses the Home button to close applications. Should your application have conditions in which it cannot provide its intended function, the recommended approach is to display an alert for the user that indicates the nature of the problem and possible actions the user could take — turning on WiFi, enabling Location Services, etc. Allow the user to terminate the application at their own discretion.

WARNING: Do not call the exit function. Applications calling exit will appear to the user to have crashed, rather than performing a graceful termination and animating back to the Home screen.

Additionally, data may not be saved, because -applicationWillTerminate: and similar UIApplicationDelegate methods will not be invoked if you call exit.

If during development or testing it is necessary to terminate your application, the abort function, or assert macro is recommended

Answer 6

On the iPhone there is no concept of quitting an app. The only action that should cause an app to quit is touching the Home button on the phone, and that's not something developers have access to.

According to Apple, your app should not terminate on its own. Since the user did not hit the Home button, any return to the Home screen gives the user the impression that your app crashed. This is confusing, non-standard behavior and should be avoided.