在UIAlertAction的处理程序中，自我应该被捕获为强者吗？ [英] Should self be captured as strong in a UIAlertAction's handler?

问题描述

当写处理程序关闭 UIAlertAction 时，应该引用 self 强（默认），弱，或无主？

When writing the handler closure of a UIAlertAction, should the reference to self be strong (the default), weak, or unowned?

有与此主题相关的帖子（ 1 ， 2 ， 3 ， 4 ）但老实说，在这种情况下我不明白他们是如何帮助的。

There have been posts relevant to this topic (1, 2, 3, 4) but I honestly don't see how they help in this case.

让我们关注这个典型的代码：

Let's focus on this typical code:

func tappedQuitButton() {
    let alert = UIAlertController(title: "Confirm quit", message: nil, preferredStyle: .ActionSheet)

    let quitAction = UIAlertAction(title: "Quit", style: .Default) { (action) in
        self.dismissViewControllerAnimated(true, completion: nil)
    }
    alert.addAction(quitAction)

    let cancelAction = UIAlertAction(title: "Cancel", style: .Default) { (action) in
        self.dismissViewControllerAnimated(true, completion: nil)
    }
    alert.addAction(cancelAction)

    presentViewController(alert, animated: true, completion: nil)
}

这是 UIViewController 子类中的函数，所以 self 是视图控制器提示警报。

This is a function inside a UIViewController subclass, so self is the view controller presenting the alert.

文档说：

使用弱引用来避免引用周期参考没有价值在其生命的某个方面。如果引用始终具有值，请改用无主引用。

Use a weak reference to avoid reference cycles whenever it is possible for that reference to have "no value" at some point in its life. If the reference will always have a value, use an unowned reference instead.

我可能会失明，但我仍然看不出这有助于回答我关于 UIAlertAction <的问题/ code>。

I may be blind, but I still don't see how this helps answering my question about UIAlertAction.

在上面的代码中， self 是否有可能在其生命的某个时刻为 ？是。所以我应该将 self 标记为 weak 。

In the above code, is it possible for self to be nil at some point in its life? Yes. So I should mark self as weak.

但是然后再次，我想不出一个看似合理的情况，当调用闭包时， self 将为nil。因此，就该关闭而言， self 将始终具有值。所以我应该将 self 标记为无主。

But then again, I can't think of a plausible scenario where self will be nil when the closure is called. So as far as that closure is concerned, self will always have a value. So I should mark self as unowned.

那么，再次，如何在UIAlertAction的处理程序中捕获 self ？

So, again, how should self be captured in a UIAlertAction's handler?

推荐答案

要问自己的关键问题是你的警报对象是否由自己拥有。在这种情况下，它不是（因为你在函数体中声明了 let alert = ... ）。因此，您不需要将其创建为弱或无主参考。

The key question to ask yourself is if your alert object is "owned" by self. In this case, it is not (because you declared let alert = ... in the function body). So you do not need to create this as a weak or unowned reference.

如果alert是self的属性，那么它将由self拥有，即当你想要在警报的拥有的闭包中创建一个弱的自我引用时。

If alert was a property of self, then it would be "owned" by self and that is when you would want to create a weak reference to self in the closure "owned" by the alert.

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