在Swift中，重置didSet中的属性会触发另一个didSet吗? [英] In Swift, does resetting the property inside didSet trigger another didSet?

问题描述

我正在测试，看来如果您在didSet中更改值，则不会再调用didSet.

I'm testing this and it appears that if you change the value within didSet, you do not get another call to didSet.

var x: Int = 0 {
    didSet {
        if x == 9 { x = 10 }
    }
}

我可以依靠吗?是否记录在某处?我没有在 Swift编程语言文档中看到它.

Can I rely on this? Is it documented somewhere? I don't see it in the Swift Programming Language document.

推荐答案

我还认为这是不可能的(也许在Swift 2中不是)，但是我对其进行了测试并找到了

I also thought, that this is not possible (maybe it wasn't in Swift 2), but I tested it and found an example where Apple uses this. (At "Querying and Setting Type Properties")

struct AudioChannel {
    static let thresholdLevel = 10
    static var maxInputLevelForAllChannels = 0
    var currentLevel: Int = 0 {
        didSet {
            if currentLevel > AudioChannel.thresholdLevel {
                // cap the new audio level to the threshold level
                currentLevel = AudioChannel.thresholdLevel
            }
            if currentLevel > AudioChannel.maxInputLevelForAllChannels {
                // store this as the new overall maximum input level
                AudioChannel.maxInputLevelForAllChannels = currentLevel
            }
        }
    }
}

在这段代码下，有以下注释:

And below this piece of code, there is the following note:

在这两项检查中的第一项中，didSet观察器将currentLevel设置为不同的值. 这不是，但是，使观察者再次被呼叫.

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