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?
This question is related to
ios
objective-c
iphone
cocoa-touch
ipad
Have you tried exit(0)?
Alternatively, [[NSThread mainThread] exit], although I have not tried that it seems like the more appropriate solution.
Apple say:
"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."
I think that this is a bad assumption. If the user tap a quit button and a message appears that say something like: "The application will now quit.", it doesn't appear to be crashed. Apple should provide a valid way to quit an application (not exit(0)).
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.
[[UIApplication sharedApplication] terminateWithSuccess];
It worked fine and automatically calls
- (void)applicationWillTerminateUIApplication *)application delegate.
to remove compile time warning add this code
@interface UIApplication(MyExtras)
- (void)terminateWithSuccess;
@end
You should not directly call the function exit(0) as it will quit the application immediately and will look like your app is crashed. So better to show users a confirmation alert and let them do this themselves.
func askForQuit(_ completion:@escaping (_ canQuit: Bool) -> Void) {
let alert = UIAlertController(title: "Confirmation!", message: "Do you want to quit the application", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Yes", style: UIAlertAction.Style.default, handler: { (action) in
alert.dismiss(animated: true, completion: nil)
completion(true)
}))
alert.addAction(UIAlertAction(title: "No", style: UIAlertAction.Style.cancel, handler: { (action) in
alert.dismiss(animated: true, completion: nil)
completion(false)
}))
self.present(alert, animated: true, completion: nil)
}
/// Will quit the application with animation
func quit() {
UIApplication.shared.perform(#selector(NSXPCConnection.suspend))
/// Sleep for a while to let the app goes in background
sleep(2)
exit(0)
}
self.askForQuit { (canQuit) in
if canQuit {
self.quit()
}
}
Its not really a way to quit the program, but a way to force people to quit.
UIAlertView *anAlert = [[UIAlertView alloc] initWithTitle:@"Hit Home Button to Exit" message:@"Tell em why they're quiting" delegate:self cancelButtonTitle:nil otherButtonTitles:nil];
[anAlert show];
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.
Go to your info.plist and check the key "Application does not run in background". This time when the user clicks the home button, the application exits completely.
- (IBAction)logOutButton:(id)sender
{
//show confirmation message to user
CustomAlert* alert = [[CustomAlert alloc] initWithTitle:@"Confirmation" message:@"Do you want to exit?" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
alert.style = AlertStyleWhite;
[alert setFontName:@"Helvetica" fontColor:[UIColor blackColor] fontShadowColor:[UIColor clearColor]];
[alert show];
}
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex != 0) // 0 == the cancel button
{
//home button press programmatically
UIApplication *app = [UIApplication sharedApplication];
[app performSelector:@selector(suspend)];
//wait 2 seconds while app is going background
[NSThread sleepForTimeInterval:2.0];
//exit app when app is in background
NSLog(@"exit(0)");
exit(0);
}
}
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.
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
Add UIApplicationExitsOnSuspend property on application-info.plist to true.
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.
After some tests, I can say the following:
[UIApplication sharedApplication] will cause the app looking like it crashed, BUT it will call - (void)applicationWillTerminate:(UIApplication *)application before doing so;exit(0); will also terminate the application, but it will look "normal" (the springboard's icons appears like expected, with the zoom out effect), BUT it won't call the - (void)applicationWillTerminate:(UIApplication *)application delegate method.My advice:
- (void)applicationWillTerminate:(UIApplication *)application on the delegate.exit(0);.Its not really a way to quit the program, but a way to force people to quit.
UIAlertView *anAlert = [[UIAlertView alloc] initWithTitle:@"Hit Home Button to Exit" message:@"Tell em why they're quiting" delegate:self cancelButtonTitle:nil otherButtonTitles:nil];
[anAlert show];
Hm, you may 'have to' quit the application if, say, your application requires an internet connection. You could display an alert and then do something like this:
if ([[UIApplication sharedApplication] respondsToSelector:@selector(terminate)]) {
[[UIApplication sharedApplication] performSelector:@selector(terminate)];
} else {
kill(getpid(), SIGINT);
}
Exit an app other way
I did this helper, though, that use no private stuff:
Exit(0);
My App has been rejected recently bc I've used an undocumented method. Literally:
"Unfortunately it cannot be added to the App Store because it is using a private API. Use of non-public APIs, which as outlined in the iPhone Developer Program License Agreement section 3.3.1 is prohibited:
"3.3.1 Applications may only use Documented APIs in the manner prescribed by Apple and must not use or call any private APIs."
The non-public API that is included in your application is terminateWithSuccess"
[[UIApplication sharedApplication] terminateWithSuccess];
It worked fine and automatically calls
- (void)applicationWillTerminateUIApplication *)application delegate.
to remove compile time warning add this code
@interface UIApplication(MyExtras)
- (void)terminateWithSuccess;
@end
We can not quit app using exit(0), abort() functions, as Apple strongly discourage the use of these functions. Though you can use this functions for development or testing purpose.
If during development or testing it is necessary to terminate your application, the abort function, or assert macro is recommended
Please find this Apple Q&A thread to get more information.
As use of this function create impression like application is crashing. So i got some suggestion like we can display Alert with termination message to aware user about closing the app, due to unavailability of certain functionality.
But iOS Human Interface Guideline for Starting And Stopping App, suggesting that Never use Quit or Close button to terminate Application. Rather then that they are suggesting to display proper message to explain situation.
An iOS app never displays a Close or Quit option. People stop using an app when they switch to another app, return to the Home screen, or put their devices in sleep mode.
Never quit an iOS app programmatically. People tend to interpret this as a crash. If something prevents your app from functioning as intended, you need to tell users about the situation and explain what they can do about it.
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
exitfunction. Applications callingexitwill 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 similarUIApplicationDelegatemethods will not be invoked if you call exit.If during development or testing it is necessary to terminate your application, the
abortfunction, orassertmacro is recommended
Exit an app other way than the home button is really non-iOS-esque approach.
I did this helper, though, that use no private stuff:
void crash()
{ [[NSMutableArray new] addObject:NSStringFromClass(nil)]; }
But still not meant for production in my case. It is for testing crash reportings, or to fast restart after a Core Data reset. Just made it safe not to be rejected if function left in the production code.
Add UIApplicationExitsOnSuspend property on application-info.plist to true.
Hm, you may 'have to' quit the application if, say, your application requires an internet connection. You could display an alert and then do something like this:
if ([[UIApplication sharedApplication] respondsToSelector:@selector(terminate)]) {
[[UIApplication sharedApplication] performSelector:@selector(terminate)];
} else {
kill(getpid(), SIGINT);
}
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.
In iPadOS 13 you can now close all scene sessions like this:
for session in UIApplication.shared.openSessions {
UIApplication.shared.requestSceneSessionDestruction(session, options: nil, errorHandler: nil)
}
This will call applicationWillTerminate(_ application: UIApplication) on your app delegate and terminate the app in the end.
But beware of two things:
This is certainly not meant to be used for closing all scenes. (see https://developer.apple.com/design/human-interface-guidelines/ios/system-capabilities/multiple-windows/)
It compiles and runs fine on iOS 13 on an iPhone, but seems to do nothing.
More info about scenes in iOS/iPadOS 13: https://developer.apple.com/documentation/uikit/app_and_environment/scenes
After some tests, I can say the following:
[UIApplication sharedApplication] will cause the app looking like it crashed, BUT it will call - (void)applicationWillTerminate:(UIApplication *)application before doing so;exit(0); will also terminate the application, but it will look "normal" (the springboard's icons appears like expected, with the zoom out effect), BUT it won't call the - (void)applicationWillTerminate:(UIApplication *)application delegate method.My advice:
- (void)applicationWillTerminate:(UIApplication *)application on the delegate.exit(0);.Hm, you may 'have to' quit the application if, say, your application requires an internet connection. You could display an alert and then do something like this:
if ([[UIApplication sharedApplication] respondsToSelector:@selector(terminate)]) {
[[UIApplication sharedApplication] performSelector:@selector(terminate)];
} else {
kill(getpid(), SIGINT);
}
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.
Library called Darvin can be used.
import Darwin
exit(0) // Here you go
NB: This is not recomanded in iOS applications.
Doing this will get you crash log.
The user should decide when an app exits. I don't think it is a good user interaction when an app quits. Therefore there is no nice API for it, only the home button has one.
If there is an error: Implement it better or Notify the user. If there have to be a restart: Implement it better of Notify the user.
It sounds dumb, but it's bad practice to exit the app without letting the user decide and not notifying him. And since there is a home button for the user interaction, Apple states, there should not be 2 things for the same function (exiting an app).
exit(0) appears to a user as crashes, so show a confirmation message to user. After confirmation suspend(home button press programmatically) and wait 2 seconds while app is going background with animation then exit behind user's view
-(IBAction)doExit
{
//show confirmation message to user
UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Confirmation"
message:@"Do you want to exit?"
delegate:self
cancelButtonTitle:@"Cancel"
otherButtonTitles:@"OK", nil];
[alert show];
}
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex != 0) // 0 == the cancel button
{
//home button press programmatically
UIApplication *app = [UIApplication sharedApplication];
[app performSelector:@selector(suspend)];
//wait 2 seconds while app is going background
[NSThread sleepForTimeInterval:2.0];
//exit app when app is in background
exit(0);
}
}
Apple say:
"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."
I think that this is a bad assumption. If the user tap a quit button and a message appears that say something like: "The application will now quit.", it doesn't appear to be crashed. Apple should provide a valid way to quit an application (not exit(0)).
Your ApplicationDelegate gets notified of intentional quitting by the user:
- (void)applicationWillResignActive:(UIApplication *)application {
When I get this notification I just call
exit(0);
Which does all the work. And the best thing is, it is the useres intent to quit, which is why this should not be a problem calling it there.
On my Audio-App it was necessary to quit the app after people were syncing their device while the music was still playing. As soon as the syncing is complete I get a notification. But quitting the app right after that would actually look like a crash.
So instead I set a flag to REALLY quit the app on the next backgrounding action. Which is okay for refreshing the app after a sync.
- (IBAction)logOutButton:(id)sender
{
//show confirmation message to user
CustomAlert* alert = [[CustomAlert alloc] initWithTitle:@"Confirmation" message:@"Do you want to exit?" delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
alert.style = AlertStyleWhite;
[alert setFontName:@"Helvetica" fontColor:[UIColor blackColor] fontShadowColor:[UIColor clearColor]];
[alert show];
}
- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex != 0) // 0 == the cancel button
{
//home button press programmatically
UIApplication *app = [UIApplication sharedApplication];
[app performSelector:@selector(suspend)];
//wait 2 seconds while app is going background
[NSThread sleepForTimeInterval:2.0];
//exit app when app is in background
NSLog(@"exit(0)");
exit(0);
}
}
I used the [[NSMutableArray new] addObject:nil] approach mentioned above to force-quit (crash) the app without making a tell-tale exit(0) function call.
Why? Because my app uses certificate pinning on all network API calls to prevent man-in-the-middle attacks. These include the initialization calls my financial app makes on startup.
If certificate authentication fails, all of my initialization calls error out and leave my app in an indeterminate state. Letting the user go home and then back into the app doesn't help, as unless the app has been purged by the OS it's still uninitialized and untrustworthy.
So, in this one case, we deemed it best to pop an alert informing the user that the app is operating in an insecure environment and then, when they hit "Close", force quit the app using the aforementioned method.
The user should decide when an app exits. I don't think it is a good user interaction when an app quits. Therefore there is no nice API for it, only the home button has one.
If there is an error: Implement it better or Notify the user. If there have to be a restart: Implement it better of Notify the user.
It sounds dumb, but it's bad practice to exit the app without letting the user decide and not notifying him. And since there is a home button for the user interaction, Apple states, there should not be 2 things for the same function (exiting an app).
Go to your info.plist and check the key "Application does not run in background". This time when the user clicks the home button, the application exits completely.
Your ApplicationDelegate gets notified of intentional quitting by the user:
- (void)applicationWillResignActive:(UIApplication *)application {
When I get this notification I just call
exit(0);
Which does all the work. And the best thing is, it is the useres intent to quit, which is why this should not be a problem calling it there.
On my Audio-App it was necessary to quit the app after people were syncing their device while the music was still playing. As soon as the syncing is complete I get a notification. But quitting the app right after that would actually look like a crash.
So instead I set a flag to REALLY quit the app on the next backgrounding action. Which is okay for refreshing the app after a sync.
You should not directly call the function exit(0) as it will quit the application immediately and will look like your app is crashed. So better to show users a confirmation alert and let them do this themselves.
func askForQuit(_ completion:@escaping (_ canQuit: Bool) -> Void) {
let alert = UIAlertController(title: "Confirmation!", message: "Do you want to quit the application", preferredStyle: .alert)
alert.addAction(UIAlertAction(title: "Yes", style: UIAlertAction.Style.default, handler: { (action) in
alert.dismiss(animated: true, completion: nil)
completion(true)
}))
alert.addAction(UIAlertAction(title: "No", style: UIAlertAction.Style.cancel, handler: { (action) in
alert.dismiss(animated: true, completion: nil)
completion(false)
}))
self.present(alert, animated: true, completion: nil)
}
/// Will quit the application with animation
func quit() {
UIApplication.shared.perform(#selector(NSXPCConnection.suspend))
/// Sleep for a while to let the app goes in background
sleep(2)
exit(0)
}
self.askForQuit { (canQuit) in
if canQuit {
self.quit()
}
}
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.
Library called Darvin can be used.
import Darwin
exit(0) // Here you go
NB: This is not recomanded in iOS applications.
Doing this will get you crash log.
We can not quit app using exit(0), abort() functions, as Apple strongly discourage the use of these functions. Though you can use this functions for development or testing purpose.
If during development or testing it is necessary to terminate your application, the abort function, or assert macro is recommended
Please find this Apple Q&A thread to get more information.
As use of this function create impression like application is crashing. So i got some suggestion like we can display Alert with termination message to aware user about closing the app, due to unavailability of certain functionality.
But iOS Human Interface Guideline for Starting And Stopping App, suggesting that Never use Quit or Close button to terminate Application. Rather then that they are suggesting to display proper message to explain situation.
An iOS app never displays a Close or Quit option. People stop using an app when they switch to another app, return to the Home screen, or put their devices in sleep mode.
Never quit an iOS app programmatically. People tend to interpret this as a crash. If something prevents your app from functioning as intended, you need to tell users about the situation and explain what they can do about it.
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.
In iPadOS 13 you can now close all scene sessions like this:
for session in UIApplication.shared.openSessions {
UIApplication.shared.requestSceneSessionDestruction(session, options: nil, errorHandler: nil)
}
This will call applicationWillTerminate(_ application: UIApplication) on your app delegate and terminate the app in the end.
But beware of two things:
This is certainly not meant to be used for closing all scenes. (see https://developer.apple.com/design/human-interface-guidelines/ios/system-capabilities/multiple-windows/)
It compiles and runs fine on iOS 13 on an iPhone, but seems to do nothing.
More info about scenes in iOS/iPadOS 13: https://developer.apple.com/documentation/uikit/app_and_environment/scenes
Exit an app other way
I did this helper, though, that use no private stuff:
Exit(0);
exit(0) appears to a user as crashes, so show a confirmation message to user. After confirmation suspend(home button press programmatically) and wait 2 seconds while app is going background with animation then exit behind user's view
-(IBAction)doExit
{
//show confirmation message to user
UIAlertView* alert = [[UIAlertView alloc] initWithTitle:@"Confirmation"
message:@"Do you want to exit?"
delegate:self
cancelButtonTitle:@"Cancel"
otherButtonTitles:@"OK", nil];
[alert show];
}
-(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex
{
if (buttonIndex != 0) // 0 == the cancel button
{
//home button press programmatically
UIApplication *app = [UIApplication sharedApplication];
[app performSelector:@selector(suspend)];
//wait 2 seconds while app is going background
[NSThread sleepForTimeInterval:2.0];
//exit app when app is in background
exit(0);
}
}
Hm, you may 'have to' quit the application if, say, your application requires an internet connection. You could display an alert and then do something like this:
if ([[UIApplication sharedApplication] respondsToSelector:@selector(terminate)]) {
[[UIApplication sharedApplication] performSelector:@selector(terminate)];
} else {
kill(getpid(), SIGINT);
}
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
exitfunction. Applications callingexitwill 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 similarUIApplicationDelegatemethods will not be invoked if you call exit.If during development or testing it is necessary to terminate your application, the
abortfunction, orassertmacro is recommended
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
My App has been rejected recently bc I've used an undocumented method. Literally:
"Unfortunately it cannot be added to the App Store because it is using a private API. Use of non-public APIs, which as outlined in the iPhone Developer Program License Agreement section 3.3.1 is prohibited:
"3.3.1 Applications may only use Documented APIs in the manner prescribed by Apple and must not use or call any private APIs."
The non-public API that is included in your application is terminateWithSuccess"
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.
Exit an app other way than the home button is really non-iOS-esque approach.
I did this helper, though, that use no private stuff:
void crash()
{ [[NSMutableArray new] addObject:NSStringFromClass(nil)]; }
But still not meant for production in my case. It is for testing crash reportings, or to fast restart after a Core Data reset. Just made it safe not to be rejected if function left in the production code.
Source: Stackoverflow.com