If i have a array of employees for example in my viewcontroller. Then I get the notification of low memory and the app is also not the active one.
At this point I should save the list of employees in a DB right ? so that when the user reactivate the app again, it will go through the viewDidLoad and from here I can reload the data from the DB?
Is this a good strategy?
I'm fairly new into iPhone dev.
You should save any unsaved changes as soon as your app enters the background. Your app could be terminated at any point in the background without ever receiving any notifications of any kind. If your data isn't saved, it will be lost when the user restarts the app.
With regard to memory warnings, these are more likely to happen in the foreground. Once your app is in the background, it is suspended and won't get any notifications. If your app is running under iOS 5 or earlier then a memory warning could result in a view controller's viewWillUnload method being called. When that view controller needs to be displayed again, its viewDidLoad will be called again. Under iOS 6, this doesn't happen anymore. viewWillUnload is deprecated.
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];
}
After an iPhone app is put into background, then the user clicks on it again and it comes back to foreground, THEN
Question - How to tell what is the current UIView/UIController after an iPhone app in brought back to foreground?
I know that the application delegate's applicationDidBecomeActive method can be used to trap the return to foreground. I also know that each controller could subscribe via notification centre to UIApplicationDidBecomeActiveNotification.
But if what I want to do is reload the UI data in the UIView/UIController that is displayed, and not carry out this same operation through all other view/controllers, how can I tell which is the one to do the reloadData on?
If your using a nav controller, you can use this:
self.navigationController.visibleViewController
When an app uses startMonitoringSignificantLocationChanges while backgrounded or when terminated, if a significant change is detected Apple states that it will bring the app back into the foreground. But, will I still be able to get the value of an ivar (previously set when the app was in the foreground) within the didUpdateToLocation CLLocationManager delegate method? Or is it lost?
If it is lost, what is the best way to persist those values after the app has terminated/backgrounded and brought back into the foreground by the location manager?
Yes of course you will. The only way you'd lose the value of that ivar is if your app has actually quit and been relaunched, at which point you're not simply coming back from the background.
Is there any possiblity for reacting to the event that a user kills your app via the multitasking bar if it has moved to the background? According to my observations, applicationWillTerminate: does NOT get called.
It seems to me that there is no possiblity for cleaning up before quitting in this case.
If an app needs to do any cleanup or shutdown, under iOS 4.x it should do this when the app's suspend delegate gets called, just before the app gets sent to the background, since there is no guarantee that the app will ever get any run time again, either due to user action or memory cleanup.
If the app's Deployment Target also includes iPhone OS 3.x, then it should also do cleanup in its terminate delegate, as that will get called instead of suspend.
It should get called. Are you depending on NSLog to tell you when it does get called? When an app goes into the inactive state by pressing the home button then any further NSLogs are not printed to the console. You could try showing a small UIAlertView to see of it does get called instead.
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.