A customisable alert view class to replace the default UIAlertController (Swift3)

AlertView.swift

public typealias AlertViewClosure = (AlertView) -> Void

// MARK: -

public final class AlertView: UIView {
    
    // MARK: - AlertViewButton
    
    public struct Button {
        
        // MARK: - Type enum
        
        public enum `Type` {
            case normal
            case confirmation
            case destructive
        }
        
        // MARK: - Properties
        
        let title: String
        let action: AlertViewClosure
        
        // MARK: - Initializer
        
        public init(withTitle title: String, ofType type: Type = .normal, onAction action: @escaping AlertViewClosure = { (alertView) in alertView.dismiss() } ) {
            self.title = title
            self.action = action
        }
        
        // MARK: -
        
        fileprivate static let `default` = Button(withTitle: "Ok") { (alertView) in alertView.dismiss() }
    }
    
    // MARK: - Type enum
    
    public enum `Type` {
        case error
        case info
    }
    
    // MARK: - Properties
    
    public let type: Type
    public let title: String?
    public let bodyText: String?
    fileprivate let buttons: [Button]
    
    // MARK: - UI Properties
    
    fileprivate let windowOverlay: UIView
    fileprivate let contentView: UIView
    fileprivate let titleLabel: UILabel
    fileprivate let bodyTextLabel: UILabel
    fileprivate var buttonViews: [UIButton] = []
    fileprivate var contentViewYCenter: NSLayoutConstraint? = nil
    
    // MARK: - Computed properties
    
    fileprivate class var mainWindow: UIWindow {
        return (UIApplication.shared.delegate?.window!)!
    }
    
    // MARK: - Initializer
    
    public init(ofType type: Type, title: String?, bodyText: String?, buttons: [Button] = [Button.default]) {
        guard buttons.count > 0 else { fatalError("No buttons provided for the AlertView") }
        guard buttons.count < 3 else { fatalError("No more than 2 buttons per AlertView") }
        
        self.type = type
        self.title = title
        self.bodyText = bodyText
        self.buttons = buttons
        
        self.windowOverlay = UIView()
        self.contentView = UIView()
        self.titleLabel = UILabel()
        self.bodyTextLabel = UILabel()
        
        super.init(frame: CGRect.zero)    }
    
    public required init?(coder aDecoder: NSCoder) {
        fatalError("'AlertView' Can be instanciated from a Nib")
    }
    
    // MARK: - UI Setup
    
    fileprivate func setupUI(inView view: UIView) {
        
        self.backgroundColor = UIColor.clear
        view.addSubview(self)
        
        self.windowOverlay.backgroundColor = UIColor.clear
        self.addSubview(self.windowOverlay)
        
        self.contentView.backgroundColor = UIColor.white
        self.contentView.layer.cornerRadius = 15.0
        self.contentView.layer.masksToBounds = true
        self.addSubview(self.contentView)
        
        self.titleLabel.text = self.title
        self.titleLabel.textAlignment = .center
        self.titleLabel.numberOfLines = 2
        self.contentView.addSubview(self.titleLabel)
        
        self.bodyTextLabel.text = self.bodyText
        self.bodyTextLabel.textAlignment = .left
        self.bodyTextLabel.numberOfLines = 0
        self.contentView.addSubview(self.bodyTextLabel)
        
        var tag: Int = 0
        for button in self.buttons {
            let buttonView: UIButton = UIButton(type: .system)
            buttonView.addTarget(self, action: #selector(AlertView.buttonTapped(sender:)), for: .touchUpInside)
            buttonView.setTitle(button.title, for: .normal)
            buttonView.tag = tag
            self.contentView.addSubview(buttonView)
            self.buttonViews.append(buttonView)
            tag += 1
        }
    }
    
    fileprivate func setupUIConstraints(inView view: UIView) {
        
        // Self
        view.addConstraint(NSLayoutConstraint(item: self, attribute: .top, relatedBy: .equal, toItem: view, attribute: .top, multiplier: 1.0, constant: 0.0))
        view.addConstraint(NSLayoutConstraint(item: self, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leading, multiplier: 1.0, constant: 0.0))
        view.addConstraint(NSLayoutConstraint(item: view, attribute: .trailing, relatedBy: .equal, toItem: self, attribute: .trailing, multiplier: 1.0, constant: 0.0))
        view.addConstraint(NSLayoutConstraint(item: view, attribute: .bottom, relatedBy: .equal, toItem: self, attribute: .bottom, multiplier: 1.0, constant: 0.0))
        self.translatesAutoresizingMaskIntoConstraints = false
        
        // Window overlay
        self.addConstraint(NSLayoutConstraint(item: self.windowOverlay, attribute: .top, relatedBy: .equal, toItem: self, attribute: .top, multiplier: 1.0, constant: 0.0))
        self.addConstraint(NSLayoutConstraint(item: self.windowOverlay, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 0.0))
        self.addConstraint(NSLayoutConstraint(item: self, attribute: .trailing, relatedBy: .equal, toItem: self.windowOverlay, attribute: .trailing, multiplier: 1.0, constant: 0.0))
        self.addConstraint(NSLayoutConstraint(item: self, attribute: .bottom, relatedBy: .equal, toItem: self.windowOverlay, attribute: .bottom, multiplier: 1.0, constant: 0.0))
        self.windowOverlay.translatesAutoresizingMaskIntoConstraints = false
        
        // Content
        let contentViewYCenter = NSLayoutConstraint(item: self, attribute: .centerY, relatedBy: .equal, toItem: self.contentView, attribute: .centerY, multiplier: 1.0, constant: 0.0)
        self.contentViewYCenter = contentViewYCenter
        self.addConstraint(contentViewYCenter)
        self.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .leading, relatedBy: .equal, toItem: self, attribute: .leading, multiplier: 1.0, constant: 45.0))
        self.addConstraint(NSLayoutConstraint(item: self, attribute: .trailing, relatedBy: .equal, toItem: self.contentView, attribute: .trailing, multiplier: 1.0, constant: 45.0))
        self.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .height, relatedBy: .lessThanOrEqual, toItem: self, attribute: .height, multiplier: 1.0, constant: -90.0))
        self.contentView.translatesAutoresizingMaskIntoConstraints = false
        
        // Title
        self.contentView.addConstraint(NSLayoutConstraint(item: self.titleLabel, attribute: .top, relatedBy: .equal, toItem: self.contentView, attribute: .top, multiplier: 1.0, constant: 15.0))
        self.contentView.addConstraint(NSLayoutConstraint(item: self.titleLabel, attribute: .leading, relatedBy: .equal, toItem: self.contentView, attribute: .leading, multiplier: 1.0, constant: 15.0))
        self.contentView.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .trailing, relatedBy: .equal, toItem: self.titleLabel, attribute: .trailing, multiplier: 1.0, constant: 15.0))
        self.titleLabel.translatesAutoresizingMaskIntoConstraints = false
        
        // Body
        self.contentView.addConstraint(NSLayoutConstraint(item: self.bodyTextLabel, attribute: .top, relatedBy: .equal, toItem: self.titleLabel, attribute: .bottom, multiplier: 1.0, constant: 15.0))
        self.contentView.addConstraint(NSLayoutConstraint(item: self.bodyTextLabel, attribute: .leading, relatedBy: .equal, toItem: self.contentView, attribute: .leading, multiplier: 1.0, constant: 15.0))
        self.contentView.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .trailing, relatedBy: .equal, toItem: self.bodyTextLabel, attribute: .trailing, multiplier: 1.0, constant: 15.0))
        self.bodyTextLabel.translatesAutoresizingMaskIntoConstraints = false
        
        // Buttons
        var leftButton: UIButton? = nil
        for button in self.buttonViews {
            if let leftButton = leftButton {
                self.contentView.addConstraint(NSLayoutConstraint(item: button, attribute: .leading, relatedBy: .equal, toItem: leftButton, attribute: .trailing, multiplier: 1.0, constant: 0.0))
                self.contentView.addConstraint(NSLayoutConstraint(item: leftButton, attribute: .width, relatedBy: .equal, toItem: button, attribute: .width, multiplier: 1.0, constant: 0.0))
            } else {
                self.contentView.addConstraint(NSLayoutConstraint(item: button, attribute: .leading, relatedBy: .equal, toItem: self.contentView, attribute: .leading, multiplier: 1.0, constant: 0.0))
            }
            self.contentView.addConstraint(NSLayoutConstraint(item: button, attribute: .top, relatedBy: .equal, toItem: self.bodyTextLabel, attribute: .bottom, multiplier: 1.0, constant: 15.0))
            self.contentView.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .bottom, relatedBy: .equal, toItem: button, attribute: .bottom, multiplier: 1.0, constant: 15.0))
            button.addConstraint(NSLayoutConstraint(item: button, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 50.0))
            button.translatesAutoresizingMaskIntoConstraints = false
            leftButton = button
        }
        if let leftButton = leftButton {
            self.contentView.addConstraint(NSLayoutConstraint(item: self.contentView, attribute: .trailing, relatedBy: .equal, toItem: leftButton, attribute: .trailing, multiplier: 1.0, constant: 0.0))
        }
    }
    
    // MARK: - Actions
    
    @objc fileprivate func buttonTapped(sender: UIButton) {
        let tag = sender.tag
        self.buttons[tag].action(self)
    }
    
    // MARK: - Presentation
    
    public func present(animated: Bool = true, inView view: UIView = AlertView.mainWindow) {
        
        self.setupUI(inView: view)
        self.setupUIConstraints(inView: view)
        
        self.contentViewYCenter?.constant = -view.bounds.height
        self.layoutIfNeeded()
        self.contentViewYCenter?.constant = 0.0
        UIView.animate(withDuration: 0.3, delay: 0.0, usingSpringWithDamping: 0.75, initialSpringVelocity: 1.0, options: .curveLinear, animations: {
            self.windowOverlay.layer.backgroundColor = UIColor(white: 0.0, alpha: 0.5).cgColor
            self.layoutIfNeeded()
        }, completion: nil)
    }
    
    public func dismiss(animated: Bool = true, onCompletion completion: @escaping Closure = { _ in }) {
        guard let superview = self.superview else {
            completion()
            return
        }
        
        self.contentViewYCenter?.constant = -superview.bounds.height
        UIView.animate(withDuration: 0.3, delay: 0.0, usingSpringWithDamping: 0.75, initialSpringVelocity: 1.0, options: .curveLinear, animations: {
            self.windowOverlay.layer.backgroundColor = UIColor.clear.cgColor
            self.layoutIfNeeded()
        }, completion: { _ in
            self.removeFromSuperview()
            completion()
        })
    }
}