開發Android必須得清楚Android生命週期才能很好的掌控程式的框架，讓整個專案思路更加清晰流暢，因此IOS也是必須要了解IOS的生命週期

先從一個簡單的例項來看看

AppDelegate.m檔案裡面的內容如下：

//
//  AppDelegate.m
//  SwitchView
//
//  Created by Pishum on 15/5/5.
//  Copyright (c) 2015年 Pishum. All rights reserved.
//

#import "AppDelegate.h"
#import "ViewController.h"
@interface AppDelegate ()
{
//    ViewController *main;
//    UINavigationController *nav;
}
@end

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    NSLog(@"APP   didFinishLaunchingWithOptions");
    
    
    
//    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
//    // Override point for customization after application launch.
//    
//    _storyBoard  = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
//    
//    main = [_storyBoard instantiateViewControllerWithIdentifier:@"main"];
//    nav = [[UINavigationController alloc] initWithRootViewController: main];
//    [self.window addSubview:nav.view];
    
    return YES;
}

- (void)applicationWillResignActive:(UIApplication *)application {
    // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
    // Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
    
    NSLog(@"APP   applicationWillResignActive");
}

- (void)applicationDidEnterBackground:(UIApplication *)application {
    // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
    // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
     NSLog(@"APP   applicationDidEnterBackground");
}

- (void)applicationWillEnterForeground:(UIApplication *)application {
    // Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
     NSLog(@"APP   applicationWillEnterForeground");
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
     NSLog(@"APP   applicationDidBecomeActive");
}

- (void)applicationWillTerminate:(UIApplication *)application {
    // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    
     NSLog(@"APP   applicationWillTerminate");
}

@end
 

//
//  ViewController.m
//  SwitchView
//
//  Created by Pishum on 15/5/5.
//  Copyright (c) 2015年 Pishum. All rights reserved.
//

#import "AppDelegate.h"
#import "ViewController.h"
#import "SecondViewController.h"
#import "TestXXX.h"
@interface ViewController ()
{

}
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    UIBarButtonItem *backbutton = [[UIBarButtonItem alloc]init];
    backbutton.title = @"返回列表";
    self.navigationItem.backBarButtonItem = backbutton;
    // Do any additional setup after loading the view, typically from a nib.
     NSLog(@"A    viewDidLoad");
    
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (IBAction)startNewView:(id)sender {
  
    UIButton* btn = (UIButton*)sender;

    switch (btn.tag) {
        case 1:
//            [self performSegueWithIdentifier:@"second" sender:self];

//            NSLog(@"onclick  ==%@",self.navigationController);
            break;
            
//        default:
//            break;
    }
    
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    

    if ([[segue identifier] isEqualToString:@"second"]) {
 
//        id object = @"傳入一個值";
        TestXXX *object = [[TestXXX alloc]init];
        object.name = @"xxx";
        
 
[email protected]"22";
        [[segue destinationViewController] setPrevData:object];
    }

}




- (void)viewDidUnload{
    NSLog(@"A   viewDidUnload");
}

- (void)viewWillAppear:(BOOL)animated{
    NSLog(@"A   viewWillAppear");
}

- (void)viewDidAppear:(BOOL)animated{
    NSLog(@"A   viewDidAppear");
}

- (void)viewWillDisappear:(BOOL)animated{
    NSLog(@"A   viewWillDisappear");
}

- (void)viewDidDisappear:(BOOL)animated{
    NSLog(@"A   viewDidDisappear");
}

@end


 

//
//  SecondViewController.m
//  SwitchView
//
//  Created by Pishum on 15/5/5.
//  Copyright (c) 2015年 Pishum. All rights reserved.
//

#import "SecondViewController.h"

@interface SecondViewController (){

}

@end

@implementation SecondViewController
//TestXXX *test;
//NSString* str2;

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    

    NSLog(@"B    viewDidLoad  str=%@",_str);
    NSLog(@"B    name=%@   age=%@",_test.name,_test.age);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

- (IBAction)back:(id)sender {
    NSLog(@"點選了第二個btn");

   [self dismissViewControllerAnimated:YES completion:nil];
}


-(id)setPrevData:(id)sender{
    _str = sender;
    _test = sender;
    
    NSLog(@"輸出上個介面得到的資訊====%@  %@  %@",sender,_test.name,_test.age);
    return sender;
}
-(void)setThePrevData:(TestXXX*)sender{
    _test = sender;
//    return sender;
}

- (void)viewDidUnload{
    NSLog(@"B    viewDidUnload");
}

- (void)viewWillAppear:(BOOL)animated{
     NSLog(@"B    viewWillAppear");
}

- (void)viewDidAppear:(BOOL)animated{
     NSLog(@"B    viewDidAppear");
}

- (void)viewWillDisappear:(BOOL)animated{
    NSLog(@"B    viewWillDisappear");
}

- (void)viewDidDisappear:(BOOL)animated{
    NSLog(@"B    viewDidDisappear");
}



@end

下面是驗證的結果：

UIViewController生命週期

- (void)viewDidLoad；                    啟動

- (void)viewDidUnload；                    

- (void)viewWillAppear:(BOOL)animated；            (很常用)    

- (void)viewDidAppear:(BOOL)animated；            更新檢視

- (void)viewWillDisappear:(BOOL)animated；        即將消失

- (void)viewDidDisappear:(BOOL)animated；        O已經消失

啟動
APP   didFinishLaunchingWithOptions
A    viewDidLoad
A   viewWillAppear
A   viewDidAppear
APP   applicationDidBecomeActive


點選Home鍵
APP   applicationWillResignActive
APP   applicationDidEnterBackground

重新進來
APP   applicationWillEnterForeground
APP   applicationDidBecomeActive


點選按鍵進入B介面
B    viewDidLoad
A   viewWillDisappear
B    viewWillAppear
B    viewDidAppear
A   viewDidDisappear


點選了第二個btn返回到A介面
B    viewWillDisappear
A   viewWillAppear
A   viewDidAppear
B    viewDidDisappear


在B介面雙擊Home然後清理程式
APP   applicationWillResignActive
APP   applicationDidEnterBackground
B    viewWillDisappear
B    viewDidDisappear
APP   applicationWillTerminate

從上面得出的結果很清晰的可以看到，點選home鍵是對UIViewController裡面的生命週期執行沒有任何影響的

只有在介面切換的時候才發現執行了某些方法。

自己不放也做個測試，親身體會下各種情況，很有用的

工程原始碼地址

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