Identify that an App is entering the background

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I have an app that is in Object-C and I’m trying to pass it to Swift, but I’m having some problems, one of them is Nsnotification that is not working.

In Object-C, I’m using it as follows:

- (void)viewDidLoad{
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(applicationDidEnterBackground:) name:UIApplicationDidEnterBackgroundNotification object:nil];
    [super viewDidLoad];
}

- (void) applicationDidEnterBackground:(NSNotification*)notification {
    NSLog(@"Entro em back");
}

In Swift I’m trying this way, but this not calling the function:

override func viewDidLoad() {
    super.viewDidLoad()
    NSNotificationCenter.defaultCenter().addObserver(self, selector: "applicationDidEnterBackground", name: UIApplicationDidEnterBackgroundNotification, object: nil)
 }

func applicationDidEnterBackground() {
    println("Entro em back")
}

In my case, I need to upload information to Nsuserdefaults when the app loads and saves user-changed information when the app enters the background.

Note: I can’t access any of the two functions.

ios mobile swift apple
  • 3

    The code is working perfectly. Probably your View Controller is not being instantiated correctly. Check where it is instantiated.

  • 1

    It is not easier to use delegate of AppDelegate?

  • @I don’t know, is it usual? The guy who taught me to 'program' for IOS said that it was not common to make changes in Appdelegate, so much so that in the project Objective-C I had to create the NSNotification

  • @Rafaelleão am not with the code here, but I created in Viewcontroller which is created as default in the project. She is blank yet! rs

  • 1

    @Davidbatista good, these methods are in the AppDelegate just for this purpose. There are the two you need, both applicationDidEnterBackground how much applicationWillEnterForeground.

  • @Paulorodrigues now the question is... how to access the information of my Viewcontroller by the 'Appdelegate'?

  • @Paulorodrigues These methods are only interesting in some cases, in others the notifications are more interesting.

  • 1

    @Davidbatista Just a friendly Minder: don’t use NSUserDefaults for different things of user preferences and App settings.

  • @fpg1503 sorry but did not understand! ... In my case it is to store two screen information ('String' / 'Int')... that the user can change.

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1 answer

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Actually your code for a detail is wrong.

Realize that the method applicationDidEnterBackground: has an argument and just like in Objective-C, from the moment your method has arguments, you must mention them in the selector separated by : to sign the selector correctly, so your code should look like this:

NSNotificationCenter.defaultCenter().addObserver(self, selector: "applicationDidEnterBackground:", name: UIApplicationDidEnterBackgroundNotification, object: nil)

Note : at the end of the method signature.

I hope I’ve helped.

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