ios - swift 3 : DispatchQueue Timing over URLSession

Question

我正在尝试创建一个用于将图像上传到我的服务器的进度指示器!我的目标是让包含 UIProgressView 和 UILabel 的 UIView 显示正在上传的照片的当前状态。

每次我的代码向我的服务器发送图像时，它应该循环到下一张图片，同时更新 UILabel(引用 lblImagesRemaining)和 UIProgressView(引用 progressImages)。

我能够让 UIView(给定引用 viewUploadBox)出现并稍微更新进度，但我似乎无法将其发送给 完全工作。 viewUploadBox 将出现，但 lblImagesRemaining 和 progressImages 都不会更新，直到上传过程完成约 70%。不过，一旦它确实达到了 ~70% 的完成度，它就会在每次发送图像时进行更新。

这是触发 Upload Test 按钮之前我的 UIViewController:

这是我的 UIViewController 一旦首次触发 Upload Test 按钮:

上传过程完成约 70% 后，这是我的 UIViewController:

这是我的代码:

@IBAction func uploadTest(_ sender: Any) {
        let imageCount = collectImages() // Collect images also prepares the tests with dictionaries for images to upload.
        DispatchQueue.main.async {
            self.viewUploadBox.isHidden = false
            self.lblImagesRemaining.text = "Images Remaining: " + String(imageCount)
            self.view.alpha = 0.5
            self.viewUploadBox.alpha = 1.5
        }
        let time = DispatchTime.now() + 0.01
        DispatchQueue.main.asyncAfter(deadline: time) { // The asyncAfter was used to ensure that the viewUploadBox appeared.
            self.uploadTest(imageCount: imageCount)
        }
    }


func uploadTest(imageCount: Int) {
        let progressFactor = 1.0 / Double(imageCount)
        var i = 1
        var imagesRemaining = imageCount
        while i < 8 {
            let imageDictionary = projectHandler.testHandler.getImageDictionary(i)
            let test = imageDictionary["test"] as! String
            for (key, value) in imageDictionary {
                if key == "test" || key == "count" {
                    continue
                }
                let url = NSURL(string: "http://IMAGEUPLOADLOCATION.PHP")
                let request = NSMutableURLRequest(url: url! as URL)
                request.httpMethod = "POST"
                let boundary = generateBoundaryString()
                //define the multipart request type
                request.setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
                let image_data = UIImageJPEGRepresentation((value as! UIImage), 0.2)
                let body = NSMutableData()
                let constructedName = userdata.valueForKey("name_full") + "(ID-" + userdata.valueForKey("id_ACCOUNT") + ")"
                let parameters = [
                    "name" : constructedName,
                    "project" : projectHandler.projectName,
                    "picturefile" : key + ".jpeg",
                    "testname" : test,
                    "projectid" : projectHandler.idPROJECT,
                    "accountid" : userdata.valueForKey("id_ACCOUNT"),
                    "brazerid" : projectHandler.idBrazer]
                //define the data post parameter
                for (key, value) in parameters {
                    body.append("--\(boundary)\r\n".data(using: String.Encoding.utf8)!)
                    body.append("Content-Disposition: form-data; name=\"\(key)\"\r\n\r\n".data(using: String.Encoding.utf8)!)
                    body.append("\(value)\r\n".data(using: String.Encoding.utf8)!)
                    body.append("--\(boundary)\r\n".data(using: String.Encoding.utf8)!)
                }
                let fname = "image"
                let mimetype = "image/jpeg"
                body.append("--\(boundary)\r\n".data(using: String.Encoding.utf8)!)
                body.append("Content-Disposition:form-data; name=\"file\"; filename=\"\(fname); \"\r\n".data(using: String.Encoding.utf8)!)
                body.append("Content-Type: \(mimetype)\r\n\r\n".data(using: String.Encoding.utf8)!)
                body.append(image_data!)
                body.append("\r\n".data(using: String.Encoding.utf8)!)
                body.append("--\(boundary)--\r\n".data(using: String.Encoding.utf8)!)
                request.httpBody = body as Data
                let session = URLSession.shared
                session.dataTask(with: request as URLRequest, completionHandler: {
                    (data, response, error) in
                    if(error != nil){
                        print("error")
                    } else {
                            do {
                            let dataString = try JSONSerialization.jsonObject(with: data!, options:.allowFragments) as! [String : AnyObject]
                            print("Response: \(response!)")
                            print("Data: \(data!)")
                            print(dataString)
                        } catch {
                            print(error)
                        }
                    }
                    DispatchQueue.main.async {
                        self.progressImages.progress += Float(progressFactor)
                        imagesRemaining -= 1
                        self.lblImagesRemaining.text = "Images Remaining: " + String(imagesRemaining)
                        if imagesRemaining == 0 {
                            self.viewUploadBox.isHidden = true
                            self.btnEmail.isEnabled = true
                            self.view.alpha = 1.0
                        }
                    }
                }).resume()
            }
            i += 1
        }
    }

Answer 1

这似乎是一个竞争条件。尝试下一个片段。

import PlaygroundSupport
import Dispatch
PlaygroundPage.current.needsIndefiniteExecution = true

let q = DispatchQueue(label: "test") // serial queue

var j = 0

DispatchQueue.concurrentPerform(iterations: 10) {  i in
    q.async {
        j += 1
        DispatchQueue.main.async {
            print(i, j)
        }
    }
}

print("total",j)

检查代码，试着想象代码将打印出什么，并将结果与​​您的预期进行比较:-)

它打印

total 6
0 10
1 10
2 10
3 10
4 10
5 10
6 10
7 10
8 10
9 10

这是你期望的吗？

让我们尝试一些更高级的东西:-)

import PlaygroundSupport
import Dispatch
PlaygroundPage.current.needsIndefiniteExecution = true

let q = DispatchQueue(label: "test") // serial queue

class S {
    let q = DispatchQueue(label: "sync", attributes: .concurrent)
    private var v: Int = 0
    func add(i: Int) {
        q.async(flags: .barrier) {
            self.v += i
        }
    }
    var i: Int {
        get {
            return q.sync {
                return v
            }
        }
    }
}

let s = S()

DispatchQueue.concurrentPerform(iterations: 10) {  i in
    q.async {
        s.add(i: 1)
        let k = s.i
        DispatchQueue.main.async {
            print(i, s.i, k)
        }
    }
}

看起来好多了，但再次检查结果。

0 4 1
1 4 2
2 4 3
3 4 4
4 6 5
5 6 6
6 8 7
7 8 8
8 10 9
9 10 10

查看第二和第三“列”中的值之间的差异。第二个看起来像你的进度条，第三个是你想要的。

嗯，但是我们使用从并发调度的串行队列...让我们删除它

import Dispatch
PlaygroundPage.current.needsIndefiniteExecution = true


class S {
    let q = DispatchQueue(label: "sync", attributes: .concurrent)
    private var v: Int = 0
    func add(i: Int) {
        q.async(flags: .barrier) {
            self.v += i
        }
    }
    var i: Int {
        get {
            return q.sync {
                return v
            }
        }
    }
}

let s = S()

DispatchQueue.concurrentPerform(iterations: 10) {  i in
        s.add(i: 1)
        let k = s.i
        DispatchQueue.main.async {
            print(i, s.i, k)
        }
}

我们又回到了起点......

1 10 4
0 10 4
3 10 4
2 10 5
5 10 7
4 10 7
6 10 7
7 10 10
8 10 10
9 10 10

解决方案

import PlaygroundSupport
import Dispatch
PlaygroundPage.current.needsIndefiniteExecution = true

class S {
    let q = DispatchQueue(label: "sync", attributes: .concurrent)
    private var v: Int = 0
    func add(i: Int) {
        q.async(flags: .barrier) {
            self.v += i
            let k = self.v
            DispatchQueue.main.async {
                print("update progress", k)
            }
        }
    }
    var i: Int {
        get {
            return q.sync {
                return v
            }
        }
    }
}

let s = S()

DispatchQueue.concurrentPerform(iterations: 10) {  i in
    s.add(i: 1)
    print(i, s.i)
}

打印

0 3
1 5
2 5
3 5
4 7
5 9
8 9
7 9
6 9
9 10
update progress 1
update progress 2
update progress 3
update progress 4
update progress 5
update progress 6
update progress 7
update progress 8
update progress 9
update progress 10

无法保证并发任务的完成顺序，但会正确指示我们的进度。