效果图如下：

分析所需的ui元素

弹窗标题ui实现

class MyTitleLabel: UILabel {

    override init(frame: CGRect) {
        super.init(frame: frame)
        configure()
    }
    
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    init(textAlignment: NSTextAlignment, fontSize: CGFloat) {
        super.init(frame: .zero)
        self.textAlignment = textAlignment
        self.font = UIFont.systemFont(ofSize: fontSize, weight: .bold)
        configure()
    }
    
    
    private func configure() {
        textColor                   = .label
        adjustsFontSizeToFitWidth   = true
        minimumScaleFactor          = 0.9
        lineBreakMode               = .byTruncatingTail
        translatesAutoresizingMaskIntoConstraints = false
    }
}

弹窗内容ui实现

class MyBodyLabel: UILabel {

    override init(frame: CGRect) {
        super.init(frame: frame)
        configure()
    }
    
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    init(textAlignment: NSTextAlignment) {
        super.init(frame: .zero)
        self.textAlignment = textAlignment
        configure()
    }
    
    
    private func configure() {
        textColor                   = .secondaryLabel
        font                        = UIFont.preferredFont(forTextStyle: .body)
        adjustsFontSizeToFitWidth   = true
        minimumScaleFactor          = 0.75
        lineBreakMode               = .byWordWrapping
        translatesAutoresizingMaskIntoConstraints = false
    }
}

关闭按钮ui实现

class MyButton: UIButton {

    override init(frame: CGRect) {
        super.init(frame: frame)
        configure()
    }
    
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    init(backgroundColor: UIColor, title: String) {
        super.init(frame: .zero)
        self.backgroundColor = backgroundColor
        self.setTitle(title, for: .normal)
        configure()
    }
    
    
    private func configure() {
        layer.cornerRadius      = 10
        setTitleColor(.white, for: .normal)
        titleLabel?.font        = UIFont.preferredFont(forTextStyle: .headline)
        translatesAutoresizingMaskIntoConstraints = false
    }
    
    
    func set(backgroundColor: UIColor, title: String) {
        self.backgroundColor = backgroundColor
        setTitle(title, for: .normal)
    }
}

半透明背景controller，内置一个圆角UIView盛放标题、内容、关闭按钮ui空间和用auto layout布局按钮位置

关闭按钮被点击后需要关闭这个controller
关闭当前controller：dismiss(animated: true)

class MyAlertVC: UIViewController {
    
    let containerView   = UIView()
    let titleLabel      = MyTitleLabel(textAlignment: .center, fontSize: 20)
    let messageLabel    = MyBodyLabel(textAlignment: .center)
    let actionButton    = MyButton(backgroundColor: .systemPink, title: "Ok")
    
    var alertTitle: String?
    var message: String?
    var buttonTitle: String?
    
    let padding: CGFloat = 20
    
    
    init(title: String, message: String, buttonTitle: String) {
        super.init(nibName: nil, bundle: nil)
        self.alertTitle     = title
        self.message        = message
        self.buttonTitle    = buttonTitle
    }
    
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.75)
        configureContainerView()
        configureTitleLabel()
        configureActionButton()
        configureMessageLabel()
    }
    
    
    func configureContainerView() {
        view.addSubview(containerView)
        containerView.backgroundColor       = .systemBackground
        containerView.layer.cornerRadius    = 16
        containerView.layer.borderWidth     = 2
        containerView.layer.borderColor     = UIColor.white.cgColor
        containerView.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            containerView.centerYAnchor.constraint(equalTo: view.centerYAnchor),
            containerView.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            containerView.widthAnchor.constraint(equalToConstant: 280),
            containerView.heightAnchor.constraint(equalToConstant: 220)
        ])
    }
    
    
    func configureTitleLabel() {
        containerView.addSubview(titleLabel)
        titleLabel.text = alertTitle ?? "Something went wrong"
        
        NSLayoutConstraint.activate([
            titleLabel.topAnchor.constraint(equalTo: containerView.topAnchor, constant: padding),
            titleLabel.leadingAnchor.constraint(equalTo: containerView.leadingAnchor, constant: padding),
            titleLabel.trailingAnchor.constraint(equalTo: containerView.trailingAnchor, constant: -padding),
            titleLabel.heightAnchor.constraint(equalToConstant: 28)
        ])
    }
    
    
    func configureActionButton() {
        containerView.addSubview(actionButton)
        actionButton.setTitle(buttonTitle ?? "Ok", for: .normal)
        actionButton.addTarget(self, action: #selector(dismissVC), for: .touchUpInside)
        
        NSLayoutConstraint.activate([
            actionButton.bottomAnchor.constraint(equalTo: containerView.bottomAnchor, constant: -padding),
            actionButton.leadingAnchor.constraint(equalTo: containerView.leadingAnchor, constant: padding),
            actionButton.trailingAnchor.constraint(equalTo: containerView.trailingAnchor, constant: -padding),
            actionButton.heightAnchor.constraint(equalToConstant: 44)
        ])
    }
    
    
    func configureMessageLabel() {
        containerView.addSubview(messageLabel)
        messageLabel.text           = message ?? "Unable to complete request"
        messageLabel.numberOfLines  = 4
        
        NSLayoutConstraint.activate([
            messageLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 8),
            messageLabel.leadingAnchor.constraint(equalTo: containerView.leadingAnchor, constant: padding),
            messageLabel.trailingAnchor.constraint(equalTo: containerView.trailingAnchor, constant: -padding),
            messageLabel.bottomAnchor.constraint(equalTo: actionButton.topAnchor, constant: -12)
        ])
    }
    
    
    @objc func dismissVC() {
        dismiss(animated: true)
    }
}

创建controller实例使用这个弹窗

let alertVC = MyAlertVC(title: title, message: message, buttonTitle: buttonTitle)
alertVC.modalPresentationStyle  = .overFullScreen
alertVC.modalTransitionStyle    = .crossDissolve
self.present(alertVC, animated: true)

一些注意的点

1. 在异步请求中使用这个弹窗需要DispatchQueue.main.async确保在主线程中

参考资料

1. https://stackoverflow.com/questions/38874517/how-to-make-a-simple-rounded-button-in-storyboard