Cocos2D and applicationWillEnterForeground

When waking up i.e. relaunching an app (either through springboard, app switching or URL)applicationWillEnterForeground: is called. It is only executed once when the app becomes ready for use, after being put into the background, while applicationDidBecomeActive: may be called multiple times after launch. This makes applicationWillEnterForeground: ideal for setup that needs to occur just once after relaunch.

applicationWillEnterForeground: is called:

• when app is relaunched
• before applicationDidBecomeActive:

applicationDidBecomeActive: is called:

• when app is first launched after application:didFinishLaunchingWithOptions:
• after applicationWillEnterForeground: if there's no URL to handle.
• after application:handleOpenURL: is called.
• after applicationWillResignActive: if user ignores interruption like a phone call or SMS.

applicationWillResignActive: is called:

• when there is an interruption like a phone call.
  • if user takes call applicationDidEnterBackground: is called.
  • if user ignores call applicationDidBecomeActive: is called.
• when the home button is pressed or user switches apps.
• docs say you should
  • pause ongoing tasks
  • disable timers
  • pause a game
  • reduce OpenGL frame rates

applicationDidEnterBackground: is called:

• after applicationWillResignActive:
• docs say you should:
  • release shared resources
  • save user data
  • invalidate timers
  • save app state so you can restore it if app is terminated.
  • disable UI updates
• you have 5 seconds to do what you need to and return the method
  • if you dont return within ~5 seconds the app is terminated.
  • you can ask for more time with beginBackgroundTaskWithExpirationHandler:

- (void)applicationWillEnterForeground:(UIApplication *)application
{
 [[CCDirector sharedDirector] resume];
 [[CCDirector sharedDirector] startAnimation];
}

- (void) applicationDidEnterBackground:(UIApplication *)application
{
 [[CCDirector sharedDirector] stopAnimation];
 [[CCDirector sharedDirector] pause];
}

- (void)applicationWillResignActive:(UIApplication *)application {
 [[CCDirector sharedDirector] stopAnimation];
 [[CCDirector sharedDirector] pause];
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
 [[CCDirector sharedDirector] stopAnimation]; // Avoid 2 Display Link Crash ***
 [[CCDirector sharedDirector] resume];
 [[CCDirector sharedDirector] startAnimation];
}

Sources:

http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIApplicationDelegate_Protocol/Reference/Reference.html

http://stackoverflow.com/questions/3712979/applicationwillenterforeground-vs-applicationdidbecomeactive-applicationwillre

http://www.cocos2d-iphone.org/forum/topic/7326