ios - 一旦异步调用在 swift 中出现，就停止它

Question

我的这个loadingOverlay 单例版本有一些问题。

应该发生的事情是它出现在屏幕上，并带有一个 View 和一个带有文本“正在加载，请稍候”的标签。或类似的东西。然后，如果加载时间超过 2 秒(我已将其更改为 10 秒以进行调试)，则文本将更改为随机的可爱短语。

首先，应该改变文本的动画似乎没有发生。相反，文本会立即改变。

更重要的是，如果由于某种原因，我的异步调用 block 被执行多次，我只希望最近一次调用它运行，并且我希望它的先前实例在运行之前终止。

我正在阅读有关回调和 promise 的内容，它们看起来很有希望。这是一个可以快速遵循的模式吗？

顺便说一句，在我学习swift和iOS的过程中，我一直在尝试，我尝试过[unowned self]现在我正在尝试[弱 self ]，但我不太确定哪个在这里最合适。

// from http://stackoverflow.com/questions/33064908/adding-removing-a-view-overlay-in-swift/33064946#33064946

import UIKit

class LoadingOverlay{
    static let sharedInstance = LoadingOverlay()

    //above swifty singleton syntax from http://krakendev.io/blog/the-right-way-to-write-a-singleton

    var overlayView = UIView()

    var spring: CASpringAnimation!
    var springAway: CASpringAnimation!

    var hidden = false

    private init() {} //This line prevents others from using the default () initializer for this class

    func setupSpringAnimation(startY: CGFloat, finishY: CGFloat) {
        overlayView.layer.position.y = startY
        spring = CASpringAnimation(keyPath: "position.y")
        spring.damping = 10
        spring.fromValue =  startY
        spring.toValue = finishY
        spring.duration = 1.0
        spring.fillMode = kCAFillModeBackwards


    }

    func showOverlay() {
        print("show overlay")
        overlayView.alpha = 1
        hidden = false
        if  let appDelegate = UIApplication.sharedApplication().delegate as? AppDelegate,
            let window = appDelegate.window {

            setupSpringAnimation(-window.frame.height / 2, finishY: window.frame.height / 2)
            let overlayViewFramesize = 0.65 * min(window.frame.height, window.frame.width)
            overlayView.frame = CGRectMake(0, 0, overlayViewFramesize, overlayViewFramesize)
            overlayView.center = window.center
            overlayView.backgroundColor = UIColor.greenColor()
            overlayView.clipsToBounds = true
            overlayView.layer.cornerRadius = overlayViewFramesize / 8

            let label = UILabel(frame: CGRectMake(0,0,overlayViewFramesize * 0.8 , overlayViewFramesize))
            label.text = " \nLoading, please wait\n "
            label.tag = 12
            overlayView.addSubview(label)
            label.lineBreakMode = NSLineBreakMode.ByWordWrapping
            label.numberOfLines = 0 //as many as needed


            label.sizeToFit()
            label.textAlignment = NSTextAlignment.Center

            label.center = CGPointMake(overlayViewFramesize / 2, overlayViewFramesize / 2)
            overlayView.bringSubviewToFront(label)
            window.addSubview(overlayView)

            overlayView.layer.addAnimation(spring, forKey: nil)
            RunAfterDelay(10.0) {
                if self.hidden == true { return }

                //strongSelf boilerplate code technique from https://www.raywenderlich.com/133102/swift-style-guide-april-2016-update?utm_source=raywenderlich.com+Weekly&utm_campaign=ea47726fdd-raywenderlich_com_Weekly4_26_2016&utm_medium=email&utm_term=0_83b6edc87f-ea47726fdd-415681129

                UIView.animateWithDuration(2, delay: 0, options: [UIViewAnimationOptions.CurveEaseInOut, UIViewAnimationOptions.BeginFromCurrentState, UIViewAnimationOptions.TransitionCrossDissolve], animations: { [weak self] in
                    guard let strongSelf = self else { return }
                    (strongSelf.overlayView.viewWithTag(12) as! UILabel).text = randomPhrase()
                    (strongSelf.overlayView.viewWithTag(12) as! UILabel).sizeToFit()
                    print ((strongSelf.overlayView.viewWithTag(12) as! UILabel).bounds.width)
                    (strongSelf.overlayView.viewWithTag(12) as! UILabel).center = CGPointMake(overlayViewFramesize / 2, overlayViewFramesize / 2)

                    }, completion: { (finished: Bool)in
                        print ("animation to change label occured")})

            }




        }
    }
    func hideOverlayView() {
        hidden = true
        UIView.animateWithDuration(1.0, delay: 0.0, options: [UIViewAnimationOptions.BeginFromCurrentState], animations: { [unowned self] in
//I know this is clunky... what's the right way?
            (self.overlayView.viewWithTag(12) as! UILabel).text = ""
            self.overlayView.alpha = 0
        }) { [unowned self] _  in
//I know this is clunky. what's the right way?                
            for view in self.overlayView.subviews {
                view.removeFromSuperview()
            }

            self.overlayView.removeFromSuperview()

            print("overlayView after removing:", self.overlayView.description)

        }

        //here i have to deinitialize stuff to prepare for the next use


    }

    deinit {
        print("Loading Overlay deinit")
    }


}

Answer 1

我基本上想要的是能够延迟一段代码，并可能在执行之前取消它。我在这里找到了答案:

GCD and Delayed Invoking