How to check if your iOS App comes into the foreground or background

I’ve been battling with those AppDelegate methods for a while, thinking “I wish there was a way that I don’t have to use those methods”. And guess what: there is!

Instead of adding code where it doesn’t make sense, we can listen to a system wide notification that tells us our app has come into the foreground, like so:

// observer checks if we're back from the background
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(myMethod) name:UIApplicationWillEnterForegroundNotification object:nil];

Here the selector “myMethod” is called when our app is about to enter the foreground. Some of the interesting notifications are

• UIApplicationDidEnterBackground
• UIApplicationDidEnterForeground
• UIApplicationWillTerminate

Find many more in Apple’s UIApplication Class Reference:

• https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplication_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006728-CH3-DontLinkElementID_4
• http://stackoverflow.com/questions/4846822/iphone-use-of-background-foreground-methods-in-appdelegate