以自定义垂直距离水平居中子视图| Swift

import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建父视图
        let containerView = UIView()
        containerView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(containerView)
        
        // 创建子视图
        let subview = UIView()
        subview.translatesAutoresizingMaskIntoConstraints = false
        subview.backgroundColor = .red
        containerView.addSubview(subview)
        
        // 设置子视图的约束条件
        NSLayoutConstraint.activate([
            // 子视图垂直居中
            subview.centerYAnchor.constraint(equalTo: containerView.centerYAnchor),
            // 子视图水平居中
            subview.centerXAnchor.constraint(equalTo: containerView.centerXAnchor),
            // 子视图高度为100
            subview.heightAnchor.constraint(equalToConstant: 100),
            // 子视图宽度为100
            subview.widthAnchor.constraint(equalToConstant: 100)
        ])
    }
}