UIScreen（屏幕）、UIWindow（画框）、UIView(画布)、didFinishLaunchingWithOptions的概念

//didFinishLaunchingWithOptions 方法：顾名思义。在app开始运行时会调用里面的方法。
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    //返回的是带有状态栏的矩形
    self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
   
    CGRect bound = [[UIScreen mainScreen]bounds];  //返回的是带有状态栏的Rect
    NSLog(@"boundwith:%f    boundheight:%f",bound.size.width,bound.size.height); 
    NSLog(@"boundx:%f    boundy:%f",bound.origin.x,bound.origin.y); 
    //2012-08-03 23:21:45.716 DinkMixer[599:c07] boundwith:320.000000    boundheight:480.000000
    //2012-08-03 23:21:45.719 DinkMixer[599:c07] boundx:0.000000    boundy:0.000000

CGRect appBound = [[UIScreen mainScreen]applicationFrame];  //返回的是不带有状态栏的Rect
    NSLog(@"appBoundwith:%f    boundheight:%f",appBound.size.width,appBound.size.height); 
    NSLog(@"appBoundx:%f    boundy:%f",appBound.origin.x,appBound.origin.y);
    //2012-08-03 23:21:45.720 DinkMixer[599:c07] appBoundwith:320.000000    boundheight:460.000000
    //2012-08-03 23:21:45.720 DinkMixer[599:c07] appBoundx:0.000000    boundy:20.000000

//很明显状态栏占用了空间20像素
  
    MasterViewController *masterViewController = [[[MasterViewController alloc] initWithNibName:@"MasterViewController" bundle:nil] autorelease];//根据nib文件的名称来创建一个视图控制器

self.navigationController = [[[UINavigationController alloc] initWithRootViewController:masterViewController] autorelease];//创建一个导航控制器，并指定该导航控制器的根视图控制器为上面建立的masterViewController

self.window.rootViewController = self.navigationController;//窗体（window）有一个根视图控制器——这个视图控制器负责配置当窗体显示时最先显示的视图。要让你的视图控制器的内容显示在窗体中，需要去设置窗体的根视图控制器为你的视图控制器。
   
    [self.window makeKeyAndVisible];//这行代码会让包含了视图控制器视图的Window窗口显示在屏幕上。
    return YES;
}

转自:http://blog.sina.com.cn/s/blog_74f70b7901017f9t.html