为什么不应该直接扩展UIView或UIViewController? [英] Why should not directly extend UIView or UIViewController?

问题描述

我看到了这个

I saw this question, with this code:

protocol Flashable {}

extension Flashable where Self: UIView 
{
    func flash() {
        UIView.animate(withDuration: 0.3, delay: 0, options: .curveEaseIn, animations: {
            self.alpha = 1.0 //Object fades in
        }) { (animationComplete) in
            if animationComplete == true {
                UIView.animate(withDuration: 0.3, delay: 2.0, options: .curveEaseOut, animations: {
                    self.alpha = 0.0 //Object fades out
                    }, completion: nil)
            }
        }
    }
}

我想知道为什么我们不只是直接扩展UIView?或在类似情况下扩展UIViewController为何用where Self:

And I wonder why do we you not just directly just extend UIView? Or in similar cases extend UIViewController why twist it around with a where Self:

• 是否是为了增加我们的意图，当其他开发人员来访时，他们会看到嘿此类符合Flashable，Dimable等标准吗?
• 我们的UIView还会有单独的有意义的扩展吗?而不是UIView或UIViewController的不同的未命名扩展?
• 关于POP这个主题，苹果是否有任何具体的指导方针?我见过那里的开发人员以这种方式这样做，但不确定为什么...

推荐答案

这种方法比直接使用UIView更可取，例如

This approach is preferable to using UIView directly, as in

extension UIView {
    func flash() {
        ...
    }
}

因为它使程序员可以决定要创建Flashable的哪些UIView子类，而不是将flash功能批发"添加到所有UIView:

because it lets programmers decide which UIView subclasses they wish to make Flashable, as opposed to adding flash functionality "wholesale" to all UIViews:

// This class has flashing functionality
class MyViewWithFlashing : UIView, Flashable {
    ...
}
// This class does not have flashing functionality
class MyView : UIView {
    ...
}

从本质上讲，这是一种选择加入"方法，而另一种方法则强制了该功能而没有选择退出"的方法.

Essentially, this is an "opt in" approach, while the alternative approach forces the functionality without a way to "opt out".

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