Swift：将 UIButton 转换为 UIBarButtonItem，真的有必要这么复杂吗？

Question

我写了一个扩展，UIButton可以将 a 转换UIButton为UIBarButtonItem.

我尝试使用传递按钮init(customView来实现最简单的解决方案，如下所示：UIBarButtonItem

lazy var myButton: UIButton = { 
    let button = UIButton(type: .custom)
    // setting up button here...
    return button
}()

let barButtonItem = UIBarButtonItem(customView: myButton)

但我遇到了一些限制问题。其实我不想只放一个按钮，而是想在导航栏中放三个项目。所以我尝试将三个按钮放入 aUIStackView然后设置，这在 iOS 10 上navigationItem.rightBarButtonItem = UIBarButtonItem(customView: stackView)就像一个魅力。但在iOS 9上，按钮的位置不起作用。

无论如何，我求助于使用UIBarButtonItem而不是UIButtons，但我不想UIBarButton为 iOS 9 创建 s，而是UIButton为 iOS 10 创建 s。所以我编写了一个UIBarButtonItem从 s 创建 s的扩展UIButton。这启用了此代码。

处理 iOS 9 和 iOS 10 的解决方案

func setupNavigationBar() {
    if #available(iOS 10.0, *) {
        let stackView: UIStackView = [.views(buttons)] //syntax enabled by framework `ViewComposer`: github.com/Sajjon/ViewComposer
        navigationItem.rightBarButtonItem = UIBarButtonItem(customView: stackView)
    } else {
        navigationItem.rightBarButtonItems = buttons.reversed().flatMap { $0.barButtonItem } // syntax enabled by extension below
    }
}

这是我的扩展代码。

扩展 UIButton

extension UIButton {

    var barButtonItem: UIBarButtonItem? {
        return barButtonItem()
    }

    func barButtonItem(
        style: UIBarButtonItemStyle = .plain,
        state: UIControlState = .normal,
        controlEvent: UIControlEvents = .primaryActionTriggered
        ) -> UIBarButtonItem? {

        guard
            let target = allTargets.first,
            let selectorName = actions(forTarget: target, forControlEvent: controlEvent)?.first,
            case let image = image(for: state), case let title = title(for: state),
            (image != nil || title != nil)
            else { return nil }

        let action = NSSelectorFromString(selectorName)

        if let image = image {
            return UIBarButtonItem(image: image, style: style, target: target, action: action)
        }

        if let title = title {
            return UIBarButtonItem(title: title, style: style, target: target, action: action)
        }

        return nil //should not happen
    }
}

问题 1：为什么将 UIButtons 放置在 UIStackView 中在 iOS 9 上不起作用？

问题 2：我的扩展是否过于复杂？或者不知何故缺乏安全感？

Answer 1

扩展可以简化

extension UIButton {
    func toBarButtonItem() -> UIBarButtonItem? {
        return UIBarButtonItem(customView: self)
    }
}