What's the best way to detect when the app is entering the background for my view?

I have a view controller that uses an NSTimer to execute some code.

What's the best way to detect when the app is going to the background so I can pause the timer?

Solution 1:

You can have any class interested in when the app goes into the background receive notifications. This is a good alternative to coupling these classes with the AppDelegate.

When initializing said classes:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillResignActive:) name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillTerminate:) name:UIApplicationWillTerminateNotification object:nil];

Responding to the notifications

-(void)appWillResignActive:(NSNotification*)note
{

}
-(void)appWillTerminate:(NSNotification*)note
{
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillResignActiveNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillTerminateNotification object:nil];

}

Solution 2:

In Swift 4.0

override func viewDidLoad() {
    super.viewDidLoad()

    let app = UIApplication.shared

    //Register for the applicationWillResignActive anywhere in your app.
    NotificationCenter.default.addObserver(self, selector: #selector(ViewController.applicationWillResignActive(notification:)), name: NSNotification.Name.UIApplicationWillResignActive, object: app)
}

@objc func applicationWillResignActive(notification: NSNotification) {

}