UI基础 UIWindow

@implementation AppDelegate


- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
//    窗户在工程创建好就存在了 我需要创建程序的第一个页面并且添加到窗户上
    //创建第一个页面
    FirstViewController* first =[[FirstViewController alloc]init];
    
    //添加到窗户上（指定根视图）
    self.window.rootViewController=first;
    
    
    
    
    
    return YES;
}

@implementation FirstViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    //更改背景颜色
    self.view.backgroundColor=[UIColor yellowColor];
    
    
 
}