I have an app (a game) which saves data: game state, high scores, achievements, etc. Currently the app delegate does this on applicationWillTerminate:. After playing around with iPhone 4 for a bit, it seems that applications pretty much never terminate: they just run in the background forever, unless the user goes out of their way to quit them, or restart the phone.
So my question is, should I find another place to save my data, and if so, when?
To minimize the amount of time spent in the delegate method call, you should find a place that makes sense to save during the game (level completion, checkpoints, etc). You can also add a new delegate method to your application delegate which will be called when your application transitions to the background where you can duplicate some of the things you may have done previously in applicationWillTerminate:. The new delegate method to implement is -applicationDidEnterBackground:.
You will also receive a notification that the user switched back to your app as applicationWillEnterForeground:.
you can do so in the views diddisappear delegate method
-(void)viewDidDisappear:(BOOL)animated
{
//CODE FOR SAVING
}
There are 2 App delegate methods you can use
applicationDidResignActive: //pausing the app, used when a msg comes up. if multitasking this wont help
applicationDidEnterBackground: // called in iOS 4 for when the app is in the background
you can see when it loads into the foreground using
applicationWillEnterForeground:
check out the reference for more info
You should save in applicationDidEnterBackground. Make sure to wrap your saving code with – beginBackgroundTaskWithExpirationHandler: and endBackgroundTask, since without that, you have less than a second (or something like that) before execution suspends.
Related
If I stop using my app for a long time then go back to it, it seems like the viewDidLoad method is being called again, even though I never "exited" the app (by pressing the home key twice and tapping the X) nor did I reboot the iPhone. If I just go to the home screen and then open the app again after a short time this does not happen. What is going on?
This has to do with the way that the operating system manages memory and how it deals with having many different apps open at one time. In a short summary, if your app is in the background for a long period of time, eventually, the OS will decide that it is inactive, and the memory associated with its view will be marked for reuse somewhere else where it is more needed. This is the viewDidUnload method in your view controller. Any time the viewDidUnload method is called, the viewDidLoad method will be called again so that you get a chance to reload your view before the user sees it.
Edit:
You cannot rely on this phenomenon happening every x minutes. It will only happen as the OS requires more memory for active apps. If you want to make sure the user always gets updated information when he or she resumes usage of your app, use NSNotificationCenter and register for the UIApplicationDidBecomeActive notification.
You can try to monitor the memory waring. Most of situation like this is memory warning get trigger and viewDidUnload get called after that if the view is not the top most. So when you back to that view, viewDidLoad will get called again.
You can try to override this method in UIViewController and see if memory warning get called. It maybe triggered by some other component in your application.
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
Looking at the example in Beginning iOS 5 for persisting your application state, in the first viewController that is shown for the app, they register for applicationWillResignActive in viewDidLoad:. So that makes sense to me in that you register for that notification when your first view is shown.
I'm confused on whether you always do this, or where you typically register for this notification. Q1) Like do they register for this notification in this viewController so they can recreate this view? Q2) If so, do I do this for each viewController?
Q3) I'm using UIStoryboard and my first viewController is a UITabBarController. So do I register for the notification in the first tab's viewController?
I also have a singleton DataManager object that holds the data for the app if that helps anyone guide me in the right direction of where I should save my data. Thanks!
These methods are in the AppDelegate.m
- (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.
*/
}
You can perform your actions here. You can however register to "listen" to that event in another view controller (like your example) but that is just to make it easier to send that event notification into that viewcontroller.
1) no, only to ensure that whenver this VC is loaded it will be able to listen to this event.
2) no, only for the ones you want to pass the even easily like this. However using the appdelegate.m and each's vc view did appear is better.
3) depends on the kind of data you want to save, but typically you create your own file and just save it to disk like in any other OS. ios gives you access to the "documents" folder of your app and each folder is used for something specific, read the documentation.
In my app from applicationDidEnterBackground i want to ask the application for more time to
create a UIWebView and load request with UIBackgroundTaskIdentifier, then in the delegate
method of UIWebView (webViewDidFinishLoad) i want to do a stuff there and show an alert or
notification while the
application is still reining in the background .
so how i can do that?.
Apple's documentation for UIApplication class for beginBackgroundTaskWithExpirationHandler: method says:
You can call this method at any point in your application’s execution.
You may also call this method multiple times to mark the beginning of
several background tasks that run in parallel. However, each task must
be ended separately. You identify a given task using the value
returned by this method.
This method can be safely called on a non-main thread.
So, once web view finish loading in background you can trigger another operation from webViewDidFinishLoad to show alert.
When you receive applicationDidEneterBackground your app is already effectively in the background. At that moment all your networking should be closed and you really shouldn't try to show any alerts or notifications.
I'm wondering if iOS allows one to do the following:
I have a puzzle game and I've been working on saving data when the user returns to the home screen. To do this, using NSNotificationCenter, I had one of my game classes to observe [UIApplication sharedApplication]'s ApplicationWillResignActive method so when that happens I save my game state. But if the user decides to exit while animations are going on, the game will save a midState where the model values are still changing and that will often cause crashes. My question is if it is possible to somehow delay the saving process (even though it is on the background) until the animations are complete (or some variable equals 1)?
My first idea is to create scheduled event with NSTimer to try to save until everything is set. Any ideas would be appreciated. Thank you
You can use performSelector:withObject:afterDelay:
// Call doSomething after a 1 second delay
[self performSelector:#selector(doSomething) withObject:nil afterDelay:1.0f];
Rather than trying to delay the saving, especially in ApplicationWillResignActive, you should look into how to stop the animation and record the expected final values of the animation. Depending on the method of animation (UIView static methods, block based, 3rd party) there is usually a way to stop them, and since you define what the animation does you should already know the final state.
In the case of block based animations:
How to cancel UIViews block-based animation?
I have put NSLogs in all my classes including my UIApplicationDelegate subclass. I am curious - and a bit nervous - about why I am not seeing them echo anything when I press the home button. I am running in the XCode simulator.
Since iPhone/iPad runs a single app at a time, doesn't hitting the home button discard all traces of the running app?
Thanks,
Doug
Chuck is correct, the dealloc's don't matter at that point. If you want to do something as your app is expiring, implement this in your app delegate class:
- (void)applicationWillTerminate:(UIApplication *)application {
// goodbye...
}
When an app is terminated, its memory is simply freed. Dealloc is not called, it does not pass go or collect $200. This is normal and intended.
You should implement -(void)applicationWillTerminate:(UIApplication*)application{
}
this method will get called when user hit home button.
You might also want to think about the additional multitasking support that has been announced. Obviously the details are still under NDA, but pushing Home does not necessarily stop your app.
And think about the various circumstances where your app may already be terminated quickly (e.g. if a call comes in and the system runs out of RAM). Do your cleanup with the application lifecycle messages.