为什么didSet中没有无限循环?

问题描述

在我的FirstViewController中，我有一个指向我的SecondViewController的按钮，将数据传递到SecondViewController中的一个属性.该属性具有属性观察器，设置后会创建SecondViewController的新实例.

In my FirstViewController I have a button directing to my SecondViewController, passing data to a property in the SecondViewController. This property has a property observer, creating a new instance of the SecondViewController when set.

尽管它可以按我的方式工作，但我想知道为什么它不会陷入无限循环中，从而永远创建SecondViewController的实例.这样做是一种好习惯吗?

While it's working as I want, I wonder why it's not getting stuck in an infinite loop, creating an instance of the SecondViewController forever. And is it good practice to do it this way?

FirstViewController:

FirstViewController:

class FirstViewController: UIViewController {
    @IBAction func something(sender: UIButton) {
        let destination = storyboard?.instantiateViewControllerWithIdentifier("secondViewController") as SecondViewController
        destination.selected = 1
        showViewController(destination, sender: self)
    }
}

SecondViewController:

SecondViewController:

class SecondViewController: UIViewController {
    var selected: Int = 0 {
        didSet {
            let destination = storyboard?.instantiateViewControllerWithIdentifier("secondViewController") as SecondViewController
            destination.selected = selected
            showViewController(destination, sender: self)
        }
    }

    @IBAction func something(sender: UIButton) {
        selected = 2
    }
}

推荐答案

如果您在 Swift编程语言-属性，Apple表示:

If you check Apple's documentation for Swift in The Swift Programming Language - Properties, Apple says that:

如果您在其自己的didSet观察器中为属性分配值，则您分配的新值将替换刚刚设置的值.

If you assign a value to a property within its own didSet observer, the new value that you assign will replace the one that was just set.

因此，如果您在didSet块的第一行中放置一个断点，则我相信它只能被调用一次.

So if you put a breakpoint in the first line of your didSet block, I believe it should only be called once.

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