//程序啟動(dòng)流程
    //main
    //UIApplicationMain
    //初始化UIAppliaction（創(chuàng)建&設(shè)置代理&開(kāi)啟Runloop）
    //監(jiān)聽(tīng)系統(tǒng)事件
    //didFinishLaunchingWithOptions
    //applicationWillResignActive
    //... 

    //創(chuàng)建UIWindow
    //創(chuàng)建控制器的View
    //將控制器的View添加到window上

    //infoplist文件中如果有Main storyboard file base name:Main 則會(huì)加載MainStoryboard
    //加載之前創(chuàng)建一個(gè)窗口UIWindow
    //把MainStoryboard所指向的控制器設(shè)置為窗口window的根控制器
    //顯示窗口Window(根控制器的view添加到window上)

    self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
    
    self.window.layer.backgroundColor = [UIColor redColor].CGColor;
    
    UIViewController *vc = [[UIViewController alloc] init];
    vc.view.backgroundColor = [UIColor grayColor];
    
    self.window.rootViewController = vc;
    
    //設(shè)置應(yīng)用程序的主窗口(在此之前window是隱藏的)
    [self.window makeKeyAndVisible];
    //相當(dāng)于下面兩行代碼
    //self.window.hidden = NO;
    //[self.window addSubview:vc.view];
    NSLog(@"%@",[UIApplication sharedApplication].delegate.window);