Controller的创建及view的创建

Controller 控制器

控制器常见的创建方式有以下几种:
• 通过storyboard创建:
  1.先加载storyboard文件（Test是storyboard的文件名）

  UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Test" bundle:nil];

  2.接着初始化storyboard中的控制器 初始化“初始控制器”（箭头所指的控制器）

           MJViewController *mj = [storyboard instantiateInitialViewController];

  3.通过一个标识初始化对应的控制器

  MJViewController *mj = [storyboard instantiateViewControllerWithIdentifier:@”mj"];

  - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
      // 1.创建window
      self.window=[[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
      // 2.加载storyboard,并且创建初始化控制器(箭头所指的控制器)
      UIStoryboard *story=[UIStoryboard storyboardWithName:@"Main" bundle:nil];
      //self.window.rootViewController=[story instantiateInitialViewController];    
      self.window.rootViewController=[story instantiateViewControllerWithIdentifier:@"dh"];//需要设置Storyboard ID
      // 3.显示窗口
      [self.window makeKeyAndVisible];
      
      return YES;
  }

• 直接创建

       MJViewController *mj = [[MJViewController alloc] init];

• 指定xib文件来创建

MJViewController *mj = [[MJViewController alloc] initWithNibName:@"MJViewController" bundle:nil];

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    self.window=[[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds];
    
    DHOneViewController *one=[[DHOneViewController alloc]initWithNibName:@"DHOneViewController" bundle:nil];
    self.window.rootViewController=one;
    
    [self.window makeKeyAndVisible];
    
    return YES;
}

创建xib文件，需要设置File‘s Owner，如下图：

执行如果报错：-[UIViewController _loadViewFromNibNamed:bundle:] loaded the "DHOneViewController" nib but the view outlet was not set.记得要连线，指定view，如看下图：

控制器的View

•控制器的view是延迟加载的：用到时再加载

 

•可以用isViewLoaded方法判断一个UIViewController的view是否已经被加载

 

•控制器的view加载完毕就会调用viewDidLoad方法