以编程方式创建UIView在Xcode 11.1中不起作用

Question

我想使用Xcode 11.1中的snapkit创建UIView作为容器视图，或者甚至以编程方式创建UIView，但是似乎出了点问题，我认为Apple已更改Xcode 11.x（iOS 13.x）中的UIView，因为我在以前版本的Xcode中非常容易做到这一点。

在SceneDelegate.swift中（Apple已将窗口变量从AppDelegate.swift移至SceneDelegate.swift中）

class SceneDelegate: UIResponder, UIWindowSceneDelegate {

    var window: UIWindow?

    func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        guard let _ = (scene as? UIWindowScene) else { return }
        let viewController = ViewController()
        if let windowScene = scene as? UIWindowScene {
            self.window = UIWindow(windowScene: windowScene)
            self.window?.rootViewController = viewController
            self.window?.makeKeyAndVisible()
        }
    }
}

ViewController.swift

  class ViewController: UIViewController {

    var containerView: UIView = {
        let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        view.backgroundColor = .green
        view.translatesAutoresizingMaskIntoConstraints = false
        return view
    }()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = .blue
        setUpView()
    }

    func setUpView() {
        self.view.backgroundColor = .blue
        self.view.addSubview(containerView)
        containerView.snp.makeConstraints { (make) in
            make.centerX.equalTo(self.view.snp.centerX)
            make.centerY.equalTo(self.view.snp.centerY)
        }
    }
}

和结果：

Answer 1

要使用自动布局显示视图，您需要提供所有W H X Y个满足布局引擎要求的视图。但是您错过了width和height约束。

尝试一下：

func setUpView() {
    self.view.backgroundColor = .blue
    self.view.addSubview(containerView)
    containerView.snp.makeConstraints { (make) in
        make.width.height.equalTo(100)
        make.center.equalTo(self.view)
    }
}

Answer 2

您需要设置容器视图的高度和宽度。

containerView.heightAnchor.constraint(equalToConstant: 100).isActive = true
containerView.widthAnchor.constraint(equalToConstant: 100).isActive = true