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:@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