为什么UITabBarControllerDelegate在我设置好之后呢？ [英] Why is the UITabBarControllerDelegate nil right after I set it?

问题描述

我有一个奇怪的问题涉及 UITabBarControllerDelegate 。

I have a weird issue involving UITabBarControllerDelegate.

我使用以下代码：

import UIKit

class MainTabBarController: UITabBarController {

    override func viewDidLoad() {
        super.viewDidLoad()
        self.delegate = MainTabBarControllerDelegate()
        print("did set delegate to \(self.delegate)")
    }

}

class MainTabBarControllerDelegate: NSObject, UITabBarControllerDelegate {

    func tabBarController(tabBarController: UITabBarController, didSelectViewController viewController: UIViewController) {
        print("selected: \(viewController) --> index: \(tabBarController.selectedIndex)")
    }

}

然后，在我的故事板中，我有两个简单的 UIViewControllers 的vanilla UITabBarController >连接到它。我只是想抓住标签更改事件，但由于某种原因，我的 MainTabBarController 中的委托未设置

Then, in my Storyboard I have the vanilla UITabBarController with two plain UIViewControllers connected to it. I simply want to catch the tab change events, but for some reason the delegate of my MainTabBarController doesn't get set properly.

当我使用上面的代码运行项目时，控制台输出：

When I run the project with the code from above, the console outputs:

did set delegate to nil

为什么不创建一个正确的 MainTabBarControllerDelegate ，以便其委托方法可以调用？

Why doesn't it create a proper instance of MainTabBarControllerDelegate so that its delegate methods can be called?

推荐答案

code> self.delegate = MainTabBarControllerDelegate（）您创建一个委托，并立即将其分配给委托属性，这是 weak 。所以代表得到创建，但是立即处理，因为没有什么可以强加它的参考。

Here self.delegate = MainTabBarControllerDelegate() you create a delegate and immediately assign it to the delegate property, which is weak. So the delegate gets created but then immediately disposed because there is nothing that holds a strong reference to it.

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