iOS: 學習筆記, 添加一個帶介面約束的控制器

1. 建立一個空iOS應用程式(Empty Application).

2. 添加加控制器類. 修改控制器類的viewDidLoad

- (void)viewDidLoad{    [super viewDidLoad];    //建立標題    UILabel *header = [[UILabel alloc] init];    header.text = @"歡迎來到我的世界!";    header.textAlignment = NSTextAlignmentCenter;    [self.view addSubview: header];        self.statusLabel = [[UILabel alloc] init];    self.statusLabel.text = @"準備就緒!";    [self.view addSubview: self.statusLabel];            //添加自動布局約束    UILabel *statusLabel = self.statusLabel;    [header setTranslatesAutoresizingMaskIntoConstraints: NO];    [statusLabel setTranslatesAutoresizingMaskIntoConstraints: NO];        NSMutableArray *contraits = [NSMutableArray array];    NSMutableDictionary *metrics = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@5, @"HPadding", @5, @"VPadding", @20, @"TopMargin", nil];    NSDictionary *views = NSDictionaryOfVariableBindings(header, statusLabel);    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[header]-HPadding-|" options:0 metrics:metrics views:views]];    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[statusLabel]-HPadding-|" options:0 metrics:metrics views:views]];    [contraits arrayByAddingObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[statusLabel]-HPadding-|" options:0 metrics:metrics views:views]];    [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-TopMargin-[header]-(>=0)-[statusLabel]-VPadding-|" options:0 metrics:metrics views:views]];    [self.view addConstraints: contraits];    }

3. 修改AppDelegate.m檔案

- (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];        //加入控制器    self.window.rootViewController = [[DemoViewController alloc] initWithNibName:nil bundle:nil];        [self.window makeKeyAndVisible];    return YES;}

4. 運行程式, 得到如下效果