视图不显示并使用自动布局集中

Question

我想以编程方式在我的视图控制器中添加一个视图并将其集中。我将视图作为子视图添加到父视图并启用了自动布局，但它没有显示。

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。您使用 newView.translatesAutoresizingMaskIntoConstraints = false 删除了它们。要恢复所有必需的约束，请将以下行添加到 viewDidLoad:

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

Answer 2

试试这个方法

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

Answer 3

问题来了... 首先，设置 newView 的框架，其次，您还设置了 translatesAutoresizingMaskIntoConstraints = false 所以 Xcode 不明白你想设置什么框架或约束。所以如果你设置了 frame 那么你以后就不能再添加约束了。

所以根据您的需要，最好的解决方案是：

view.addSubview(newView)
newView.translatesAutoresizingMaskIntoConstraints = false

newView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
newView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
newView.widthAnchor.constraint(equalToConstant: 200).isActive = true
newView.heightAnchor.constraint(equalToConstant: 200).isActive = true

视图不显示并使用自动布局集中

View not displaying and centralising with autolayout

ios

autolayout

swift