iOS: 学习笔记, 添加一个带界面约束的控制器

1. 创建一个空iOS应用程序(Empty Application).

2. 添加加控制器类. 修改控制器类的viewDidLoad

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     //创建标题
     UILabel *header = [[UILabel alloc] init];
     header.text = @"欢迎来到我的世界!";
     header.textAlignment = NSTextAlignmentCenter;
     [self.view addSubview: header];

     self.statusLabel = [[UILabel alloc] init];
     self.statusLabel.text = @"准备就绪!";
     [self.view addSubview: self.statusLabel];

     //添加自动布局约束
     UILabel *statusLabel = self.statusLabel;
     [header setTranslatesAutoresizingMaskIntoConstraints: NO];
     [statusLabel setTranslatesAutoresizingMaskIntoConstraints: NO];

     NSMutableArray *contraits = [NSMutableArray array];
     NSMutableDictionary *metrics = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@, @"HPadding", @, @"VPadding", @, @"TopMargin", nil];
     NSDictionary *views = NSDictionaryOfVariableBindings(header, statusLabel);
     [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[header]-HPadding-|" options: metrics:metrics views:views]];
     [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[statusLabel]-HPadding-|" options: metrics:metrics views:views]];
     [contraits arrayByAddingObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-HPadding-[statusLabel]-HPadding-|" options: metrics:metrics views:views]];
     [contraits addObjectsFromArray:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-TopMargin-[header]-(>=0)-[statusLabel]-VPadding-|" options: metrics:metrics views:views]];

     [self.view addConstraints: contraits];

 }

3. 修改AppDelegate.m文件

- (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. 运行程序, 得到如下效果