師傅發我一堆view的建立函式，目的讓我知道view的建立過程。

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
- (void)viewWillAppear:(BOOL)animated
{

}
- (void)viewDidAppear:(BOOL)animated
{

}
- (void)loadView
{

}
- (void)layoutSublayersOfLayer:(CALayer *)layer
{

}
- (void)viewWillLayoutSubviews
{

}
 - (void)viewDidLoad
{

}
 

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen] bounds]];

 
    self.window.rootViewController = [[MyViewController alloc]init];
    
    [self.window makeKeyAndVisible];
    // Override point for customization after application launch.
    return YES;
}
 

然後執行   。。。。。。涼了。。。出現錯誤了；

啟動起來黑屏，然後是報這樣一個錯誤Application windows are expected to have a root view controller at the end of application launch

2014-08-13 15:16:45.924 任務1副本[2629:60b] -[YouVC loadView]
2014-08-13 15:16:45.925 任務1副本[2629:60b] -[YouVC viewDidLoad]
2014-08-13 15:16:45.925 任務1副本[2629:60b] -[YouVC loadView]
2014-08-13 15:16:45.926 任務1副本[2629:60b] -[YouVC viewDidLoad]
2014-08-13 15:16:45.927 任務1副本[2629:60b] -[YouVC loadView]
2014-08-13 15:16:45.927 任務1副本[2629:60b] -[YouVC viewDidLoad]
2014-08-13 15:16:45.928 任務1副本[2629:60b] -[YouVC loadView]
2014-08-13 15:16:45.928 任務1副本[2629:60b] -[YouVC viewDidLoad]
2014-08-13 15:16:45.929 任務1副本[2629:60b] Application windows are expected to have a root view controller at the end of application launch
 

無解 ，網上搜得所有方案都不對。我把焦點放在了 self.window.rootviewcontroller = ....這句話上了；

我開始想它出錯的原因，為什麼這些方法呼叫了好幾遍，單步除錯發現這些函式不止是在初始化的init時候呼叫。

我又新建了一個viewcontroller就加了一個背景色，結果能執行，我又試著將師傅給的程式碼貼上去，結果又出現錯誤了。

我就開始挨個試是什麼出現了問題，最後讓我找到了原因出在-（void）loadview這個函式上面；

我又開始查詢這個函式，最後從M了個J老師這獲得了答案：

原來在每次呼叫view的時候，如果view為空，則會呼叫這個函式；他的作用就是來建立一個view，首先載入xib 如果沒有xib 則自動建立一個大小320*480 的空白view；

在程式的

-（void）loadview 中加入了[super loadview];後程序能夠運行了；

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
-(id)init
{
    if(self = [super init])
    {
        self.view.frame=[[UIScreen mainScreen]bounds];
        self.view.backgroundColor = [UIColor orangeColor];
    }
    return self;
}
- (void)loadView
{
   // [super loadView];
    NSLog(@"%s",__FUNCTION__);

}

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSLog(@"%s",__FUNCTION__);
    // Do any additional setup after loading the view from its nib.
}
- (void)viewWillAppear:(BOOL)animated
{
    NSLog(@"%s",__FUNCTION__);
}
- (void)viewDidAppear:(BOOL)animated
{
    NSLog(@"%s",__FUNCTION__);
}

- (void)layoutSublayersOfLayer:(CALayer *)layer
{
    NSLog(@"%s",__FUNCTION__);
    
}
- (void)viewWillLayoutSubviews
{
    NSLog(@"%s",__FUNCTION__);
}

執行結果：

2014-08-13 15:35:54.783 任務1副本[2660:60b] -[YouVC loadView]
2014-08-13 15:35:54.783 任務1副本[2660:60b] -[YouVC viewDidLoad]
2014-08-13 15:35:54.784 任務1副本[2660:60b] -[YouVC viewWillAppear:]
2014-08-13 15:35:54.785 任務1副本[2660:60b] -[YouVC viewWillLayoutSubviews]
2014-08-13 15:35:54.835 任務1副本[2660:60b] -[YouVC viewDidAppear:]

M了個J老師的部落格 http://www.cnblogs.com/mjios/archive/2013/02/26/2933667.html裡面詳細講述了這幾個函式；