I've been using interactive notification and it works well when my app is suspended in the background, but causes problems when my app has been terminated.
I've used NSLog to determine the app's lifecycle when the interactive notification is triggered when the app has not launched.
The following goes on, in the order listed, without the app visibly launching:
didfinishlaunching
handleActionWithIdentifier
viewdidload
viewwilllayoutsubviews
viewdidlayoutsubviews
viewdidappear
The app then seems to terminate without calling
didenterbackground or willTerminate
The reason why it's causing issues for me is because I create timers in viewdidload that are invalidated in didenterbackground.
Because didenterbackground isn't being called, when the app is subsequently launched after triggering an interactive notification I'm ending up with two instances of the timer.
Could anyone shed some light on why the app terminates but didenterbackground or willTerminate aren't being called?
You should not assume that a call to didfinishlaunching means that you are in the foreground. As #PaulW11 says in his comment, for local notifications when your app is not running, you get launched directly into the background, and never see a foreground-to-background transition, because you were never in the foreground in the first place.
The system will call applicationDidBecomeActive: if you are being launched into the foreground. You should put your code that starts your timers there.
The docs say that local notification notices get invoked in the background:
When the user taps a custom action in the alert for a remote or local
notification’s, the system calls the
application:handleActionWithIdentifier:forRemoteNotification:completionHandler:
or
application:handleActionWithIdentifier:forLocalNotification:completionHandler:
method in the background so that your app can perform the associated
action.
You should write your application:handleActionWithIdentifier:forLocalNotification:completionHandler: method to check to see if it's being called from the foreground or from the background.
I use (Objective-C) code like this to tell if I'm in the foreground or the background:
BOOL inBackground = [UIApplication sharedApplication].applicationState == UIApplicationStateBackground;
Related
currently I am testing AppDelegate methods, when they are executed by adding NSLog to every method. What is not clear to me is when method applicationWillTerminate is executed? I've tried to put app in background, then to terminate it, but log from Terminate method is not executed. What is executed is this:
2015-09-01 16:24:01.512 TestQuestions[2351:110179] didFinisLaunching
2015-09-01 16:24:02.530 TestQuestions[2351:110179] didBecomeActive
2015-09-01 16:24:05.864 TestQuestions[2351:110179] willResign
2015-09-01 16:24:06.322 TestQuestions[2351:110179] didEnterBackground
What is not clear to me is when method applicationWillTerminate is executed
Almost never. It can be called under certain rare circumstances where you are e.g. playing music in the background and are terminated from there. But in general you should expect that it will never be called, because by the time you are terminated, you are already suspended and your code is no longer running (and the system is not going to wake you up just to tell you it's killing you in the background).
One time that applicationWillTerminate will execute is when a user touches (once or twice) the Home button and then slides the app off the screen.
Personally I do this regularly since I touch the Home button to switch between regularly used apps that I want to make active, rather that finding them in my 9 pages of icons.
Our application use UIBackgroundMode "voip" so it can be launch in background.
In our case application was launched in background by iOS and application:didFinishLaunchingWithOptions was called. Then user immediately tapped to the app icon. We don't know when it actually occurred but its look like after several seconds from background launch. After that user made some work in application, interacted with UI, but application wasn't got applicationWillEnterForeground method invoke and notifications. This method was called after 30 minutes after user worked with application. And all of this time UIApplication applicationState value was UIApplicationStateBackground.
Why did applicationWillEnterForeground was called so later?
There is not steps to reproduce this situation because it is rare case. iOS Version is 8.1
I am working on an iOS app that has Multitasking enabled.Now, I want to perform some stuff when the app quits but not when it goes to the background. I understand we have following methods:
applicationWillEnterBackground:
applicationWillEnterBackground:
These methods are always called when app goes in background not necessarily getting terminated. I don't want to run my code if its in background but not terminating.
applicationWillTerminate:
This method works great if I terminate my app while in foreground or background but (according to Apple documentation) this method only gets called only when the app terminates while it is in foreground or background but not in the suspended state.
So, I would like to know how can I make my code run when the app is terminated while in suspended mode as well?
Any help would be appreciated.
Is there a way to perform some last actions when the user kills the application on iPhone?
In UIApplicationDelegate there is applicationWillTerminate: but as I understand it's not guaranteed to get called when the application terminates. Is there another way?
You can't rely on applicationWillTerminate being called. From the documentation:
For apps that do not support background execution or are linked against iOS 3.x or earlier, this method is always called when the user quits the app. For apps that support background execution, this method is generally not called when the user quits the app because the app simply moves to the background in that case. However, this method may be called in situations where the app is running in the background (not suspended) and the system needs to terminate it for some reason.
The proper place to save any state is when the app enters the background. Once that happens, there is no way to know if the app will return to the foreground or if it gets killed and then started from the beginning.
All methods concerning your app state are in your AppDelegate when you use one of the project templates.
Put the code in the applicationWillResignActive: method. It will get called if your app goes to an inactive state (terminating or no).
- (void)applicationWillResignActive:(UIApplication *)application
{
// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
// Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
}
The "correct" place to save state is in both -applicationDidEnterBackground: and -applicationWillTerminate:. Don't worry about double-saving; generally only one of them is called (IME, -applicationWillTerminate: is not called when your app is killed in the background).
Caveat: -applicationDidEnterBackground: is not guaranteed to be called, since it is called after your app enters the background (and thus becomes eligible for killing without notice!). If the device is low on memory when your app is backgrounded, it might be killed. The best way to avoid this is to not use too much memory in the first place.
You could use
-applicationWillResignActive:, but I do not recommend this: apps become inactive quite frequently. An obvious is system dialogs (location/privacy prompts, Wi-Fi, notifications that show as alerts, alarms), TWTweetSheet, and I suspect MFMailComposeViewController, MFMessageComposeViewController, Notification Center, the app-switcher bar (e.g. to change tracks/enable orientation lock).
you can use applicationWillResignActive method in the appdelegate, or you can do the following, if you want to save stuff, but for some reason, you dont want to do it in the app delegate:
- (void) viewDidLoad/init {
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(myApplicationWillResign)
name:UIApplicationWillResignActiveNotification
object:NULL];
}
- (void) myApplicationWillResign {
NSLog(#"About to die, perform last actions");
}
Which is the proper delegate to implement when an application is waking up from being in the background and you want it to prep it to be active?
applicationWillEnterForeground vs applicationDidBecomeActive -- What's the difference?
Which is the proper delegate to implement for when an application is going to sleep and you want to prep it to cleanup and save data?
applicationWillResignActive vs. applicationDidEnterBackground -- What's the difference?
Also, I've noticed that applicationWillResignActive gets called when an incoming SMS or call comes in but the user chooses to click Ok and continue. I don't want my app to take any action in these cases. I just want it to keep running without any intermediate cleanup since the user didn't exit the app. So, I would think it makes more sense to do cleanup work just in applicationDidEnterBackground.
I would appreciate your input on best practices to follow on choosing which delegates to implement for waking up and going to sleep as well as considering events like being interrupted by SMS/calls.
Thanks
When waking up i.e. relaunching an app (either through springboard, app switching or URL) applicationWillEnterForeground: is called. It is only executed once when the app becomes ready for use, after being put into the background, while applicationDidBecomeActive: may be called multiple times after launch. This makes applicationWillEnterForeground: ideal for setup that needs to occur just once after relaunch.
applicationWillEnterForeground: is called:
when app is relaunched
before applicationDidBecomeActive:
applicationDidBecomeActive: is called:
when app is first launched after application:didFinishLaunchingWithOptions:
after applicationWillEnterForeground: if there's no URL to handle.
after application:handleOpenURL: is called.
after applicationWillResignActive: if user ignores interruption like a phone call or SMS.
applicationWillResignActive: is called:
when there is an interruption like a phone call.
if user takes call applicationDidEnterBackground: is called.
if user ignores call applicationDidBecomeActive: is called.
when the home button is pressed or user switches apps.
docs say you should
pause ongoing tasks
disable timers
pause a game
reduce OpenGL frame rates
applicationDidEnterBackground: is called:
after applicationWillResignActive:
docs say you should:
release shared resources
save user data
invalidate timers
save app state so you can restore it if app is terminated.
disable UI updates
you have 5 seconds to do what you need to and return the method
if you don't return within ~5 seconds the app is terminated.
you can ask for more time with beginBackgroundTaskWithExpirationHandler:
The official documentation.
Managing Your App's Life Cycle is helpful to your questions. For quick concept, you can see Figures in that document.
You can also read the comment from the code generated by the XCode Wizard. Listed as follows:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// Override point for customization after application launch.
return YES;
}
- (void)applicationWillResignActive:(UIApplication *)application
{
/*
Sent when the application is about to move from active to inactive state.
This can occur for certain types of temporary interruptions (such as an
incoming phone call or SMS message) or when the user quits the application
and it begins the transition to the background state.
Use this method to pause ongoing tasks, disable timers, and throttle down
OpenGL ES frame rates. Games should use this method to pause the game.
*/
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
/*
Use this method to release shared resources, save user data, invalidate
timers, and store enough application state information to restore your
application to its current state in case it is terminated later.
If your application supports background execution, this method is called
instead of applicationWillTerminate: when the user quits.
*/
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
/*
Called as part of the transition from the background to the active state;
here you can undo many of the changes made on entering the background.
*/
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
/*
Restart any tasks that were paused (or not yet started) while the
application was inactive. If the application was previously in the
background, optionally refresh the user interface.
*/
}
- (void)applicationWillTerminate:(UIApplication *)application
{
/*
Called when the application is about to terminate.
Save data if appropriate.
See also applicationDidEnterBackground:.
*/
}
For more detailed explanations, please refer to official document for UIApplicationDelegate
I was still a bit confused with Dano's answer so I did a little test to get the flow of events in certain scenarios for my reference, but it might be useful to you too. This is for apps that DO NOT use UIApplicationExitsOnSuspend in their info.plist. This was conducted on an iOS 8 simulator + confirmed with iOS 7 device. Please excuse Xamarin's event handler names. They are very similar.
Initial and all subsequent launches from a not-running state:
FinishedLaunching
OnActivated
Interruption (phone call, top slide-down, bottom slide-up):
Home button double-press listing inactive apps, then reselecting our app:
OnResignActivation
OnActivated
Home button double-press listing inactive apps, selecting another app, then relaunching our app:
Home button single press, then relaunch:
Lock (on/off button), then unlock:
OnResignActivation
DidEnterBackground
WillEnterForeground
OnActivated
Home button double-press, and terminate our app: (subsequent relaunch is first case)
OnResignActivation
DidEnterBackground
DidEnterBackground (iOS 7 only?)
Yes, DidEnterBackground is called twice on iOS7 device. Both times UIApplication state is Background. However, iOS 8 simulator does not. This needs testing on iOS 8 device. I will update my answer when I get my hand on it, or someone else could confirm.
applicationWillEnterForeground is called:
when app is relaunched(comes from background to foreground)
This method is not invoked when app starts for the first time i.e when applicationDidFinishLaunch is called but only when comes from background
applicationDidBecomeActive
applicationDidBecomeActive is called
when app is first launched after didFinishLaunching
after applicationWillEnterForeground if there’s no URL to handle.
after application:handleOpenURL: is called.
after applicationWillResignActive if user ignores interruption like a phone call or SMS.
after disappearing of alertView anywhere from the application
applicationWillResignActive is called when system is asking for permissions. (in iOS 10). Just in case someone hit into the same trouble as me...
In iOS 8+ there is a subtle but important difference for taking phone call.
In iOS 7 if user takes phone call both applicationWillResignActive: and applicationDidEnterBackground: are called. But in iOS 8+ only applicationWillResignActive: is called.
For iOS 13+ the following methods will be executed:
- (void)sceneWillEnterForeground:(UIScene *)scene
- (void)sceneDidBecomeActive:(UIScene *)scene