在初次接觸iPhone開發的時候，簡直就是一頭霧水，這是哪里跟哪里啊?本是做Android開發的我，第一次建立iPhone開發而得到初始代碼，心里那糾結比我初次接觸Android的情況還要糟糕!不說那么多廢話了，第一編文章首先來熟悉一下iPhone程序的生命周期吧，這對整個開發周期也是非常有用的!

 iPhone app 與 Android app在生命周期在大體上是相同，但是不同的時Android的程序生命周期都體現在每個頁面Activity上，也就是說，在開發Android app的時候，我們只需要管理好每個頁面Activity的生命周期，app的生命周期就無需我們太操心了!而iPhone app是嚴格按照MVC模型開發出來的程序，“委托”這一概念是非常重要的，理所當然，iPhone app的生命周期也是在“委托”上實現的，我們在建立iPhone app的初始狀態就可以看到兩個文件：AppDelegate.h和AppDelegate.m!這兩個文件就是我剛剛所說的“委托”的頭文件和實現文件!AppDelegate.m上就可以看到app的生命周期所觸發全部方法!iPhone的生命周期分為兩種，一是程序的生命周期，二是視圖(也就是相當于Android的Activity)的生命周期!

首先，介紹程序的生命周期：(表述能力有待提高，上代碼最實際)

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//首次加載，觸發的方法，開始加載程序

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions

{

NSLog(@"app didFinishLaunchingWithOptions");

 self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];

 // Override point for customization after application launch.

 self.viewController = [[[ViewController alloc] initWithNibName:@"ViewController" bundle:nil] autorelease];

 self.window.rootViewController = self.viewController;

[self.window makeKeyAndVisible];

return YES;

}

//當用戶點擊菜單健，程序放棄激活狀態

 - (void)applicationWillResignActive:(UIApplication *)application

{

NSLog(@"applicationWillResignActive");

}

//進入后臺，線程被掛起

 - (void)applicationDidEnterBackground:(UIApplication *)application

{

NSLog(@"applicationDidEnterBackground");

}

 //程序未結束，點擊程序返回前臺，再次獲取激活狀態，觸發applicationDidBecomeActive方法!

 - (void)applicationWillEnterForeground:(UIApplication *)application

{

NSLog(@"applicationWillEnterForeground");

}

//完成激活，可以與用戶交互

 - (void)applicationDidBecomeActive:(UIApplication *)application

{

NSLog(@"applicationDidBecomeActive");

}

//程序結束時觸發

 - (void)applicationWillTerminate:(UIApplication *)application

{

NSLog(@"applicationWillTerminate");

}

下面讓我們看一下視圖的生命周期：

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- (void)viewDidLoad

{

[super viewDidLoad];

NSLog(@"viewDidLoad");

}

- (void)viewDidUnload

{

[super viewDidUnload];

secondViewController = nil;

NSLog(@"viewDidUnload");

}

-(void)viewWillAppear:(BOOL)animated

{

[super viewWillAppear:YES];

NSLog(@"viewWillAppear");

}

-(void)viewDidAppear:(BOOL)animated

{

[super viewDidAppear:YES];

NSLog(@"viewDidAppear");

}

-(void)viewDidDisappear:(BOOL)animated

{

[super viewDidDisappear:YES];

NSLog(@"viewDidDisappear");

}

-(void)viewWillDisappear:(BOOL)animated

{

[super viewWillDisappear:YES];

NSLog(@"viewWillDisappear");

}

從方法名，我們都可以看得出，視圖生命周期里面大概觸發的方法。

 現在我們運行一下程序，然后從第一個視圖切換到第二個視圖，再回到第一個視圖。讓我們看一下，從程序、視圖的出現，消亡所觸發的所有方法： #

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 2012-05-10 11:29:13.426 iPhoneLifeCycle[877:f803] app didFinishLaunchingWithOptions

 2012-05-10 11:29:13.459 iPhoneLifeCycle[877:f803] viewDidLoad

 2012-05-10 11:29:13.462 iPhoneLifeCycle[877:f803] viewWillAppear

 2012-05-10 11:29:13.465 iPhoneLifeCycle[877:f803] applicationDidBecomeActive

 2012-05-10 11:29:13.472 iPhoneLifeCycle[877:f803] viewDidAppear

 2012-05-10 11:29:15.054 iPhoneLifeCycle[877:f803] viewWillDisappear

 2012-05-10 11:29:15.061 iPhoneLifeCycle[877:f803] viewDidDisappear

 2012-05-10 11:29:16.476 iPhoneLifeCycle[877:f803] viewDidLoad

 2012-05-10 11:29:16.478 iPhoneLifeCycle[877:f803] viewWillAppear

 2012-05-10 11:29:16.483 iPhoneLifeCycle[877:f803] viewDidAppear

 2012-05-10 11:29:21.790 iPhoneLifeCycle[877:f803] applicationWillResignActive

 2012-05-10 11:29:21.796 iPhoneLifeCycle[877:f803] applicationDidEnterBackground