有时不使用 Swift 5 编译器调用子类中的委托方法 [英] Delegate methods in child class sometimes not called with Swift 5 compiler

问题描述

正如 sunshinejr 指出的那样 此处，此问题已修复，将与下一个 Xcode/Swift 版本一起发布.

As sunshinejr pointed out here, this has been fixed and will be released together with the next Xcode/Swift version.

在使用 Swift 4 和 Swift 5 代码库将 Xcode 10.1 更新到 Xcode 10.2 后，我看到了很多奇怪的行为.

I've seen a lot of weird behaviour after updating Xcode 10.1 to Xcode 10.2, both with Swift 4 and Swift 5 codebases.

问题之一是在一个 ViewController 上不再调用 ScrollView 委托方法.简化的视图层次如下:

One of the problems is that on one ViewController the ScrollView delegate methods are no longer called. The simplified view hierarchy is as follows:

| ScrollView (ParentScrollView)
| -- Stack View
| ---- ScrollView (ChildScrollView)
| ---- ScrollView (ChildScrollView)
| ---- ScrollView (ChildScrollView)

它充当具有多个页面的视图:ParentScrollView 可以水平滚动，ChildScrollView 可以垂直滚动.

It acts as a view with several pages: ParentScrollView can be scrolled horizontally, the ChildScrollViews vertically.

ViewController 是所有 Scrollview 的委托(在 Storyboard 中设置)，但是在滚动任何视图(ParentScrollView 或 ChildScrollView)时不会调用委托方法(如 scrollViewDidEndDecelerating).ViewController 的基类符合UIScrollViewDelegate.

The ViewController is the delegate of all Scrollviews (set in Storyboard), but the delegate methods (like scrollViewDidEndDecelerating) are not called when scrolling any of the views (ParentScrollView or ChildScrollView). The base class of ViewController conforms to UIScrollViewDelegate.

我尝试在代码中设置委托，除此之外我不知道我可能做错了什么.转换没有更改类中的任何代码，但在更新之前一切正常.在 Swift 5 Release 中，我也找不到对手势、委托或滚动视图的任何更改备注.

I have tried setting the delegates in code, other than that I have no idea what I could be doing wrong. The conversion did not change any code in the class, but everything worked well before updating. I also couldn't find any changes to gestures, delegates or ScrollViews in general in the Swift 5 Release Notes.

这似乎是 Swift 5 编译器的一个错误.此外，有时它会起作用，有时不起作用 - 无需更改任何代码或项目设置.

This seems to be a bug with the Swift 5 compiler. Additionally, sometimes it does work, sometimes it doesn't - all without changing any code or project settings.

为什么这不再起作用?有没有其他人遇到过类似的行为?

Why does this no longer work? Has anyone else experienced similar behaviour?

推荐答案

As sunshinejra> 指出此处，此问题已修复，将与下一个 Xcode/Swift 版本一起发布.

As sunshinejr pointed out here, this has been fixed and will be released together with the next Xcode/Swift version.

我发现了问题，这是重现它的方法.

I've found the issue, here's how to reproduce it.

class A: UIViewController, UIScrollViewDelegate {
    // ...does not implement 'scrollViewDidEndDecelerating'
}

class B: A {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Will not be called!
    }
}

什么有效:

class A: UIViewController, UIScrollViewDelegate {
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Probably empty
    }
}

class B: A {
    override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        // Will be called!
    }
}

如果基类没有实现委托方法，编译器似乎认为它没有实现.如果只有子类实现了，就找不到了.

The compiler seems to think that a delegate method is not implemented if the base class did not implement it. If only the child class implements it, it can't find it.

我仍然无法解释为什么这种行为在 Swift 5 中发生了变化，但至少我找到了解决方案.也许有人可以提供进一步的见解?

I still can't explain why this behaviour changed with Swift 5, but at least I've found a solution. Maybe someone can give further insights?

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