AppDelegate-> AppDelegate is a class which inherit  from UIAppDelegate and contains basics launching methods of any applications .

It contains many methods but five basic methods are given below.

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions ->This is the very first  method which starts at the time of application launch. At the time of launching we can write that code here which we need that time.

- (void)applicationWillResignActive:(UIApplication *)application -> suppose we are using one game App on which we are playing game and suddendly we got a call or message here Application was active and become inactive once call had come. If application will go from active to inactive condition then we use this.

- (void)applicationDidEnterBackground:(UIApplication *)application ->  This method calls when a running App goes to background and not doing anything.

- (void)applicationWillEnterForeground:(UIApplication *)application-> This method calls when an App resume from background to foreground.

- (void)applicationDidBecomeActive:(UIApplication *)application-> It means restart the job where you left last time

- (void)applicationWillTerminate:(UIApplication *)application-> This method is called when an App is about to terminate.