I am currently building a music app which takes controls from the iOS7 control center. One of the features I noticed is that if I press the "play" control button, my app will start, even if it has been killed. This is not something which I want to happen, so I added return NO in didFinishLaunchingWithOptions if the app is launching in the background to prevent the initialization process.
Unfortunately, this does not change the fact that the app has still started, and didFinishLaunchingWithOptions is not called again (and nothing is initialized). Since I cannot have the app forcefully kill itself when I don't want it to start, is there any way to prevent the app from launching? I had thought that returning NO would have done the trick, but this does not appear to be the case.
I have found one of the main causes to this issue. It had to do with the audio session and the various notifications/delegates which the app was registered for. In the AppDelegate's applicationWillTerminate: I had to make sure to call:
[[UIApplication sharedApplication] endReceivingRemoteControlEvents];
[[AVAudioSession sharedInstance] setActive:NO withOptions:AVAudioSessionSetActiveOptionNotifyOthersOnDeactivation error:&audioSessionError];
And also unregister for any audio notifications (interrupts and route changes).
Do you want your app to run in the background at all?
If not, you can simply add a info.plist value so it doesn't enter background and just closes when a user hits the home button.
Related
I am trying to smoothly close down my app.
First I put the app in the background and tried to use exit(0) to close down the app:
//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);
My problem is, when I check to see what apps are running in the background, the app is still there. I thought exit(0) would remove it from the background.
It appears my app is going under recently used. Is there a way to programmatically remove it from that list?
You can't programmatically remove an app from the "recently used apps" list. When a user double-taps the Home button, the list of recently used apps is just that - a list of recently used app. It has absolutely nothing at all to with whether the app is fully terminated or suspended in the background.
Calling exit(0); simply terminates your app. But it was still recently used so it appears in the list when the user double-taps the Home button.
In XCode edit the info.plist adding the setting "Application does not run in background" with a value of YES to make your application exit every time:
Setting this will add UIApplicationExitsOnSuspend to info.plist:
<key>UIApplicationExitsOnSuspend</key>
<true/>
Is there a way i could stop an app from going into background ? Or is there a way in which i could bring my app to foreground if it did go into background ?
I'm making a showcase app for a client and the app must always run on the iPad without interaction from the user.
You can force your app to stay active using following code
[[UIApplication sharedApplication] setIdleTimerDisabled:YES];
But if you press home button of device, the app will go in background. You cannot force to stop this.
In this case you can use UILocalNotification to bring the app to the foreground if the device is locked, a notification appears, and the user unlocks the device or if user tap on the notification.
You can also fire a local notification whenever user going to background in
applicationDidEnterBackground: method
Here's my app scenario: When user swipes a notification I will launch some other app via URL.
So it basically launches some other app when notification arrives.
Currently to handle swiping notification scenario, when
- (BOOL)application:(UIApplication *)app didFinishLaunchingWithOptions:(NSDictionary *)
method is invoked, within this method, I call processNotification: method, which contains:
...
[[UIApplication sharedApplication] openURL:url];
...
If push received while app is active, url is opened perfectly fine.
If push received by swiping or clicking on notification, url is opened in the background but the currently viewed app is my application. For example if my url is tel:123-456-7890, iOS starts the call (you can hear the sound) but active app is not Phone.app, it is my app.
That seemed pretty strange to me. However if I wait for UI to load, and call processNotification: after that, it brings up Phone.app window correctly. (bug in platform? because call happens but my UI is on the top.)
I need a method to delay execution of this processNotification: call, (maybe through an operation queue) until a view controller is loaded. Otherwise, my app stays on top and the URL is opened in the background.
I was facing the same issue, I moved the openURL into main_queue and it seems to be working fine. I did not have to even make that change in didBecomeActive
dispatch_async(dispatch_get_main_queue(), ^(void){
[[UIApplication sharedApplication] openURL:url];
});
You should delay your handling of the push notification (i.e. calling openURL:) until applicationDidBecomeActive:. Keep the parameters you need from application:didFinishLaunchingWithOptions: but only call your handling code in applicationDidBecomeActive:.
I think the problem here is that SpringBoard is unable to cope with one app transition being called while another is in progress. An iOS bug of course. You should open a bug report at https://bugreport.apple.com
I have an app that needs to do something when it’s sent to background using the Home button and something else when the device is locked using the top hardware button. The standard way of solving these requirements are the notifications and delegate methods sent out by UIApplication. On iOS 4 they look like this:
// Pressing the home button
Will resign active.
Did enter background.
// Tapping app icon on Springboard
Will enter foreground.
Did become active.
// Pressing the lock button
Will resign active.
// Unlocking the device
Did become active.
In other words, it’s quite easy to tell between locking and backgrounding. On iOS 5 the behaviour changed:
// Pressing the home button
Will resign active.
Did enter background.
// Tapping app icon on Springboard
Will enter foreground.
Did become active.
// Pressing the lock button
Will resign active.
Did enter background.
// Unlocking the device
Will enter foreground.
Did become active.
Notice that the didEnterBackground and willEnterForeground notifications are now sent out even when (un)locking the device, making it impossible to tell between locking and backgrounding. Is this change documented somewhere? Is it a regression? Do you know another way to distinguish the two cases?
iOS 6
In my preliminary testing via the simulator, checking the application state with
[[UIApplication sharedApplication] applicationState]
in either
- (void)applicationWillEnterForeground:(UIApplication *)application
- (void)applicationDidEnterBackground:(UIApplication *)application
allows you to differentiate between a call to lock the device and just switching back to the homescreen. A lock screen will return 1 (UIApplicationStateInactive), whereas a home button press will register as a 2 (UIApplicationStateBackground).
It seems consistent and should work on an iOS device just as reliably as it does in the simulator.
iOS 7
The iOS 6 method no longer works in iOS 7. In order to do this now, you have to utilize CFNotificationCenter and listen for a darwin notification (labeled: com.apple.springboard.lockcomplete). You can find the github repo with the sample project here: https://github.com/binarydev/ios-home-vs-lock-button
Credit for the iOS 7 fix goes out to wqq
I have looked into this quite a bit so I would love to be wrong here if someone knows something I don't, but technically, there is no documented way to tell the difference between locking the device, and sending to background.
One thing you can check however, is the UIApplicationState during the transition from foreground to background. Locking a device will give UIApplicationStateInactive and moving the App to the background will give UIApplicationStateBackground. But, since this behaviour is not officially documented it may change in the future.
A basic example:
- (void)applicationDidEnterBackground:(UIApplication *)application {
UIApplicationState state = [[UIApplication sharedApplication] applicationState];
NSLog(#"Device state: %#", state);
switch (state) {
case UIApplicationStateActive:
/* ... */
break;
case UIApplicationStateInactive:
/* Device was/is locked */
break;
case UIApplicationStateBackground:
/* User pressed home button or opened another App (from an alert/email/etc) */
break;
}
}
UIApplicationState - The running states of an application
typedef enum {
UIApplicationStateActive,
UIApplicationStateInactive,
UIApplicationStateBackground
}
UIApplicationState
Constants
UIApplicationStateActive - The application
is running in the foreground and currently receiving events. Available
in iOS 4.0 and later.
UIApplicationStateInactive - The application is running in the
foreground but is not receiving events. This might happen as a result
of an interruption or because the application is transitioning to or
from the background.
UIApplicationStateBackground - The application is
running in the background.
According to the UIApplicationDelegate Protocol Reference:
applicationWillResignActive:
didEnterBackground:
// ...
willEnterForeground:
applicationDidBecomeActive:
are the only methods that ever get called in both situations.
According to the iOS 4.3 to iOS 5.0 API Diff, these are the ONLY changes regarding UIApplication or UIApplicationDelegate, so I couldn't find where they documented any of these notification changes:
UIApplication.h
Added -[UIApplication setNewsstandIconImage:]
Added UIApplication.userInterfaceLayoutDirection
Added UIApplicationDelegate.window
Added UIApplication(UINewsstand)
Added UIApplicationLaunchOptionsNewsstandDownloadsKey
Added UIRemoteNotificationTypeNewsstandContentAvailability
Added UIUserInterfaceLayoutDirection
Added UIUserInterfaceLayoutDirectionLeftToRight
Added UIUserInterfaceLayoutDirectionRightToLeft
This is more of a workaround/hack, but according to my experience it's very reliable.
When the device is screen-locked (not just home button-ed, if that's a word :)) - bound network (UDP) sockets are broken.
I was using GCDAsyncUDPSocket (also AsyncUDPSocket before) and they both fire a network/broken pipe error reliably when the device is turned off.
In my case I need the UDP socket anyway, for other apps it might be a bit smelly, however, just binding/listening on a UDP socket without any action is not too terrible if you really need to differentiate here.
This note will [self destruct]; is 5 minutes (so Apple won't find out).
There’s a thread about this issue on Apple Developer Forums (registered developers only, sorry). The gist is that the new behaviour is by design. There are requests for a new API feature to distinguish between the two use cases, but nothing working yet.
Here is what Apple's iOS Programming Guide says:
Pressing the Sleep/Wake button is another type of interruption that
causes your app to be deactivated temporarily. When the user presses
this button, the system disables touch events, moves the app to the
background but sets the value of the app’s applicationState property
to UIApplicationStateInactive (as opposed to
UIApplicationStateBackground), and finally locks the screen.
http://developer.apple.com/library/ios/#DOCUMENTATION/iPhone/conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html
So, you should check the UIApplication's applicationState property in applicationDidEnterBackground:. If it is UIApplicationStateBackground the user pressed the home button. But if it is UIApplicationStateInactive the user locked the device.
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