ios - 如何在 Swift 中正确重构对象初始化的第一阶段？

Question

所以我在 Swift 中了解到我们应该使用两阶段初始化:https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html

规则之一是:“在第一阶段初始化完成之前，初始化程序不能调用任何实例方法、读取任何实例属性的值或将自身作为值引用。”

这可以防止在实例方法中放置代码块，所以我猜应该使用类方法？你怎么看？任何替代解决方案？

为了说明我的意思，这里有 3 个代码示例:

未重构的代码:

@objc class MYChatBarButton: UIBarButtonItem {

    let badgeLabel: UILabel


    init(target: AnyObject, selector: Selector) {

        let button = UIButton.buttonWithType(.Custom) as UIButton
        button.frame = CGRectMake(0, 0, 35, 44)
        button.addTarget(target, action: selector, forControlEvents: .TouchUpInside)
        button.tintColor = UIColor.whiteColor()
        button.setImage(UIImage(named: "chat_icon")?.imageWithRenderingMode(.AlwaysTemplate), forState: .Normal)
        button.imageEdgeInsets = UIEdgeInsets(top: 0, left: 7, bottom: 5, right: 0)

        badgeLabel = UILabel(frame: CGRectMake(0, 0, 15, 15))
        badgeLabel.backgroundColor = UIColor.clearColor()
        badgeLabel.textColor = UIColor.whiteColor()
        badgeLabel.textAlignment = .Center
        badgeLabel.text = "0"
        badgeLabel.userInteractionEnabled = false

        button.addSubview(badgeLabel)


        super.init(customView: button)


    }


}

我期望进行重构但它不起作用的方式:

@objc class MYChatBarButton: UIBarButtonItem {

    let badgeLabel: UILabel


    init(target: AnyObject, selector: Selector) {

        let button = createButton(target, selector: selector)
        createBadgeLabel()
        button.addSubview(badgeLabel)

        super.init(customView: button)


    }

    func createButton(target: AnyObject, selector: Selector) -> UIButton {
        let button = UIButton.buttonWithType(.Custom) as UIButton
        button.frame = CGRectMake(0, 0, 35, 44)
        button.addTarget(target, action: selector, forControlEvents: .TouchUpInside)
        button.tintColor = UIColor.whiteColor()
        button.setImage(UIImage(named: "chat_icon")?.imageWithRenderingMode(.AlwaysTemplate), forState: .Normal)
        button.imageEdgeInsets = UIEdgeInsets(top: 0, left: 7, bottom: 5, right: 0)
        return button
    }

    func createBadgeLabel() {
        badgeLabel = UILabel(frame: CGRectMake(0, 0, 15, 15))
        badgeLabel.backgroundColor = UIColor.clearColor()
        badgeLabel.textColor = UIColor.whiteColor()
        badgeLabel.textAlignment = .Center
        badgeLabel.text = "0"
        badgeLabel.userInteractionEnabled = false
    }

}

它可能应该完成的方式(但我不太喜欢它):

@objc class MYChatBarButton: UIBarButtonItem {

    let badgeLabel: UILabel


    init(target: AnyObject, selector: Selector) {

        let button = MYChatBarButton.createButton(target, selector: selector)
        badgeLabel = MYChatBarButton.createBadgeLabel()
        button.addSubview(badgeLabel)

        super.init(customView: button)


    }

    class func createButton(target: AnyObject, selector: Selector) -> UIButton {
        let button = UIButton.buttonWithType(.Custom) as UIButton
        button.frame = CGRectMake(0, 0, 35, 44)
        button.addTarget(target, action: selector, forControlEvents: .TouchUpInside)
        button.tintColor = UIColor.whiteColor()
        button.setImage(UIImage(named: "chat_icon")?.imageWithRenderingMode(.AlwaysTemplate), forState: .Normal)
        button.imageEdgeInsets = UIEdgeInsets(top: 0, left: 7, bottom: 5, right: 0)
        return button
    }

    class func createBadgeLabel() -> UILabel {
        let bl = UILabel(frame: CGRectMake(0, 0, 15, 15))
        bl.backgroundColor = UIColor.clearColor()
        bl.textColor = UIColor.whiteColor()
        bl.textAlignment = .Center
        bl.text = "0"
        bl.userInteractionEnabled = false
    }

}

Answer 1

至少，您可以隔离 badgeLabel 创建:

@objc class MYChatBarButton: UIBarButtonItem {

    let badgeLabel: UILabel = {
        let bl = UILabel(frame: CGRectMake(0, 0, 15, 15))
        bl.backgroundColor = UIColor.clearColor()
        bl.textColor = UIColor.whiteColor()
        bl.textAlignment = .Center
        bl.text = "0"
        bl.userInteractionEnabled = false
        return bl
    }()

    let button: UIButton = {
        let button = UIButton.buttonWithType(.Custom) as UIButton
        button.frame = CGRectMake(0, 0, 35, 44)
        button.tintColor = UIColor.whiteColor()
        button.setImage(UIImage(named: "chat_icon")?.imageWithRenderingMode(.AlwaysTemplate), forState: .Normal)
        button.imageEdgeInsets = UIEdgeInsets(top: 0, left: 7, bottom: 5, right: 0)
        return button
    }()

    init(target: AnyObject, selector: Selector) {
        button.addTarget(target, action: selector, forControlEvents: .TouchUpInside)
        button.addSubview(badgeLabel)
        super.init(customView: button)
    }

没有属性(property)我不知道该怎么做。