特定条件下不会调用类扩展中的协议方法 [英] Protocol methods in a class extension are not called under specific conditions

问题描述

我遇到了一个奇怪的行为.我能说的最好的方法是……当超类已经符合协议(通过扩展)时，不会调用类扩展中未覆盖的协议方法.但是，只有在使用 release 构建配置构建时才会发生这种情况.

A 类:UIViewController {}扩展 A: UIScrollViewDelegate {func scrollViewDidScroll(_ scrollView: UIScrollView) {打印(超类中的scrollViewDidScroll")}}B类:A{//这里设置了一个 tableView(及其数据源和委托)...}扩展 B: UITableViewDelegate {覆盖 func scrollViewDidScroll(_ scrollView: UIScrollView) {super.scrollViewDidScroll(scrollView)print("子类中的scrollViewDidScroll")}func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {打印(scrollViewDidEndDragging")}}

<块引用>

输出:

超类中的scrollViewDidScroll

子类中的scrollViewDidScroll

scrollViewDidEndDragging

但是，如果我使用 release 构建配置构建它，输出是

<块引用>

超类中的scrollViewDidScroll

子类中的scrollViewDidScroll

如果我不在类B中使用协议一致性方法的扩展，而是使用常规方式代替我可以解决问题(将实现协议的方法放入班级).

问题是……怎么会?

解决方案

我也遇到了同样的问题.

Xcode 版本 - 12.4Swift 版本 - 4.2

我还遇到只有在应用程序中调用 applicationDidBecomeActive 方法时才会显示此行为.(主要是当您导航到其他屏幕(如身份验证等)时)

修复:您需要再次将 ViewController 指定为委托.

func applicationDidBecomeActive(_ application: UIApplication) {fixForCallBackInExt()}func fixForCallBackInExt() {守卫让 navController = window?.rootViewController as?UINavigationController else { return }如果让 tabVC = navController.topViewController 作为?UITabBarController, let topVC = tabVC.selectedViewController, topVC.isKind(of: UIViewController.self) {//设置你的委托 = topVC} else if let topVC = navController.topViewController, topVC.isKind(of: UIViewController.self) {//设置你的委托 = topVC}}

I encountered a weird behavior. The best way I can put it is … Not overridden protocol methods in a class extension are not called while the superclass already conforms to the protocol (via extension). However this happens only while it's build with the release build configuration.

class A: UIViewController {}

extension A: UIScrollViewDelegate {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        print("scrollViewDidScroll in superclass")
    }
}

class B: A {
    // A tableView (and its data source and delegate) is set here…
}

extension B: UITableViewDelegate {
    override func scrollViewDidScroll(_ scrollView: UIScrollView) {
        super.scrollViewDidScroll(scrollView)
        print("scrollViewDidScroll in subclass")
    }

    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        print("scrollViewDidEndDragging")
    }
}

The output:

scrollViewDidScroll in superclass

scrollViewDidScroll in subclass

scrollViewDidEndDragging

however if I build it with the release build configuration, the output is

scrollViewDidScroll in superclass

scrollViewDidScroll in subclass

I can solve the problem if I don't use the extension for protocol conformance approach in the class B and just use the regular way instead (put the methods that implement a protocol into the class).

The question is … how come?

解决方案

I too encountered the same behaviour.

Xcode version - 12.4 Swift version - 4.2

I also encounter that this behaviour is shown only when applicationDidBecomeActive method is called in the application.(Mostly when you have navigation to some other Screen like authentication etc)

Fix: You need to assign the ViewController as delegate again.

func applicationDidBecomeActive(_ application: UIApplication) {

    fixesForCallBackInExt()
}

func fixesForCallBackInExt() {
    guard  let navController = window?.rootViewController as? UINavigationController else { return }
    if let tabVC = navController.topViewController as? UITabBarController, let topVC = tabVC.selectedViewController, topVC.isKind(of: UIViewController.self) {
        // Set Your Delegate = topVC
    } else if let topVC = navController.topViewController, topVC.isKind(of: UIViewController.self) {
        // Set Your Delegate = topVC
    }
}

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