ios - 带有 iOS 圆形进度条的 AWS S3 下载

Question

我敢打赌这是一个非常基本的问题，但我无法让它发挥作用。我正在从 AWS S3 下载图像，能够获取下载进度，并能够相应地更新进度变量。但是，我找不到基于此变量为进度条设置动画的方法。

(确实很笨拙)代码如下:

func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    self.refresh()  //re-gets user info. Having trouble with AWS randomly claiming I'm attempting to download using UnAuth even though I am logged in
    tableView.deselectRow(at: indexPath, animated: true)
    self.downloadProgressView.isHidden = false
    self.proprietaryObject = proprietaryObjects[indexPath.row]
    let expression = AWSS3TransferUtilityDownloadExpression()
    expression.progressBlock = {(task, progress) in DispatchQueue.main.async(execute: {
        self.progress = progress
    })
    }

    let transferUtility = AWSS3TransferUtility.default()
    let resource = "\(self.proprietaryObject?.value1 ?? "NA")_\(self.proprietaryObject?.value2 ?? "NA")_\(self.proprietaryObject?.firstName ?? "NA")_\(self.proprietaryObject?.lastName ?? "NA")"
    let type = "jpeg"
    self.downloadingFileURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("\(resource).\(type)")
    transferUtility.download(to: self.downloadingFileURL!, bucket: AWSS3BucketName, key: "\(resource).\(type)", expression: expression, completionHandler: { (task, URL, Data, Error) in
        if Error != nil {
            print (Error!)
        }
        if let data = Data {
            print("Data: \(data)")
            let image = UIImage(data: data)
            self.downloadedImage = image
        }
    }).continueWith(executor: AWSExecutor.default()) { (task) -> Any? in
        if let error = task.error {
            print("download error: \(error)")
            self.refresh()
        }else {
            print("Download started")
            print("User: \(self.user?.username ?? "NO USER")")
            self.animatePath()

        }
        return nil
    }
}
func animatePath() {
    print("Animation Started")
    if !(self.view.subviews.contains(downloadProgressView)) {
        self.view.addSubview(downloadProgressView)
        downloadProgressView.center = self.view.center
        self.downloadProgressView.isHidden = false
        self.downloadProgressView.layer.addSublayer(self.shapeLayer)
    }else {
        self.view.bringSubview(toFront: self.downloadProgressView)
        self.downloadProgressView.isHidden = false
        downloadProgressView.center = self.view.center
        if !((downloadProgressView.layer.sublayers?.contains(self.shapeLayer))!) {
            self.downloadProgressView.layer.addSublayer(self.shapeLayer)
        }

    }
    func animate() {
        if self.progress?.fractionCompleted == nil {
            self.fraction = 0
        }else {
            self.fraction = 0 + (self.progress?.fractionCompleted)!
        }
        let animation = CABasicAnimation(keyPath: "strokeEnd")
        animation.fromValue = CGFloat(self.shapeLayer.strokeEnd)
        animation.toValue = CGFloat(self.fraction!)
        animation.duration = 0.2
        animation.fillMode = kCAFillModeForwards
        self.shapeLayer.strokeEnd = CGFloat(self.fraction!)
        self.shapeLayer.add(animation, forKey: "animation")
    }

    DispatchQueue.main.asyncAfter(deadline: .now() + .seconds(1) , execute: {
        //the one second delay gives self.progress.fractionCompleted time to be non-nil
        repeat {
            animate()
            print("Completed: \((self.progress?.fractionCompleted)! * 100)%")
        } while self.fraction! < 1

        if self.fraction == 1 {
            print("fraction achieved 100%. resetting to 0%")
            self.fraction = 0
            self.progress = nil
            self.performSegue(withIdentifier: "proprietarySegue", sender: self)
        }
    })
}

控制台记录递增的“.fractionCompleted”%，当它达到 100% 时，它会执行转场。下面的ViewController的UIImageView中的图像确实是下载的图像(覆盖prepare for segue未显示)。但我只看到进度圈的闪烁。通常，它不会显示任何进度，然后执行 segue。在第一个 segue 之后，对于每个后续下载，downloadProgressView 不会出现，或者在消失之前显示 100% 完成。

我有一种感觉，我正在做一些根本错误的事情和/或者它与线程有关......？

如有任何帮助，我们将不胜感激。

Answer 1

self.animatePath() 已在 transferUtility 的完成 block 中调用。这就是为什么动画会在下载结束时发生并执行segue。

尝试:

let expression = AWSS3TransferUtilityDownloadExpression()
expression.progressBlock = {(task, progress) in 
    DispatchQueue.main.async(execute: {
        self.progress = progress
        self.animatePath()
    })
}