IOS学习（一）视图创建

抛弃storyBoard，纯代码- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    //大小与屏幕保持一致     self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];    [self.window setBackgroundColor:[UIColor whiteColor]];        //让window显示在手机屏幕上     [self.window makeKeyAndVisible];    //xcode7之后，必须给windwo设置一个根控制器，否则运行会报错     [self.window setRootViewController:[[MainViewController alloc] init]];                    return YES;}