在 Swift 中引用回调时防止内存泄漏

Question

注意：此问题与 Swift、闭包、回调和内存泄漏有关...其余的仅供说明。

假设我们有一个 class，ValueAnimator，它具有以下初始化程序：

init(durationInSeconds: Int, sampleRate: Int, interpolation: Interpolator,
         callback: @escaping (Double) -> Void) {
        self.maxIterations = durationInSeconds * sampleRate
        self.timeInterval = 1.0 / Double(sampleRate)
        self.interpolation = interpolation
        self.callback = callback
    }

如您所见，我们有一个传入的回调。

现在，考虑从 ViewController 初始化 ValueAnimator 时定义回调的这两种不同方式：

选项一，在线定义回调：

class ViewController: ViewController {

    var valueAnimator: ValueAnimator?

    override func viewDidLoad() {
        valueAnimator = ValueAnimator(durationInSeconds: 2, sampleRate: 2,
                                      interpolation: .sineWaveFrom0To1To0)
        { [weak self] value in
            guard let self = self else { return }

            // Do something with value ...
        }
        valueAnimator?.start()
    }

}

方案二，将回调定义为单独的函数并引用它：

（我更喜欢这种方式...因为我发现它不是 "cognitive load" 不在闭包中闭包...因此问题）

class ViewController: ViewController {

    var valueAnimator: ValueAnimator?

    override func viewDidLoad() {
        valueAnimator = ValueAnimator(durationInSeconds: 2, sampleRate: 2,
                                       interpolation: .sineWaveFrom0To1To0, callback: theCallback)
        valueAnimator?.start()
    }

    func theCallback(value: Double) {

        // Do something with the value ...

    }

}

正如您在第一个版本中看到的那样，有一些针对引用循环的保护。

是否有某种方法可以在第二个版本中应用同样的保护...或者出于某种原因没有必要？

谢谢！

Answer 1

要对第二种方式应用相同的保护，请发送 self 而不是回调，并在您的 class ValueAnimator 中定义

weak var delegate:ViewController?

然后在响应里面做

delegate?.callback(value:<#value#>)

Answer 2

您可以选择使用父委托（self）调用任何函数。

init(durationInSeconds: Int, sampleRate: Int, interpolation: Interpolator, delegate: 
AnyObject?, callback: @escaping (Double) -> Void) {
    self.maxIterations = durationInSeconds * sampleRate
    self.timeInterval = 1.0 / Double(sampleRate)
    self.interpolation = interpolation
    delegate?.callback(value: 0)
}


class ViewController: ViewController {

var valueAnimator: ValueAnimator?

override func viewDidLoad() {
    valueAnimator = ValueAnimator(durationInSeconds: 2, sampleRate: 2,
                                   interpolation: .sineWaveFrom0To1To0, delegate: self, callback: theCallback)
    valueAnimator?.start()
}

func theCallback(value: Double) {

    // Do something with the value ...

}

}

在 Swift 中引用回调时防止内存泄漏

Preventing memory leaks when referencing a callback in Swift

closures

memory-leaks

weak-references

callback

swift