iOS: 学习笔记, 加入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. 加入加控制器类. 改动控制器类的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];
    
    
    //加入自己主动布局约束
    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. 改动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];
    
    //增加控制器
    self.window.rootViewController = [[DemoViewController alloc] initWithNibName:nil bundle:nil];
    
    [self.window makeKeyAndVisible];
    return YES;
}

4. 执行程序, 得到例如以下效果