视图不显示并使用自动布局进行居中

Question

我想以编程方式在视图控制器中添加视图并将其集中。我已将该视图作为子视图添加到父视图，并启用了自动布局，但未显示。

import UIKit

class ViewController: UIViewController {
    lazy var newView:UIView = {
        let view = UIView()
        view.backgroundColor = #colorLiteral(red: 0.4745098054, green: 0.8392156959, blue: 0.9764705896, alpha: 1)
        view.frame = CGRect(x: 0, y: 0, width: 200, height: 200)
        return view
    }()


    let titleLable = UILabel()
    let bodyLabel = UILabel()
    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(newView)
        newView.translatesAutoresizingMaskIntoConstraints = false


        newView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
        newView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true



    }


}

Answer 1

newView缺少大小限制。您用newView.translatesAutoresizingMaskIntoConstraints = false删除了它们。要恢复所有必需的约束，请在viewDidLoad中添加以下行：

newView.widthAnchor.constraint(equalToConstant: 200).isActive = true
newView.heightAnchor.constraint(equalToConstant: 200).isActive = true

Answer 2

尝试这种方式

NSLayoutConstraint(item: newView,
                   attribute: NSLayoutConstraint.Attribute.centerX,
                   relatedBy: NSLayoutConstraint.Relation.equal,
                   toItem: view,
                   attribute: NSLayoutConstraint.Attribute.centerX,
                   multiplier: 1,
                   constant: 0).isActive = true

NSLayoutConstraint(item: newView,
                   attribute: NSLayoutConstraint.Attribute.centerY,
                   relatedBy: NSLayoutConstraint.Relation.equal,
                   toItem: view,
                   attribute: NSLayoutConstraint.Attribute.centerY,
                   multiplier: 1,
                   constant: 0).isActive = true