在下载数据时，有没有办法在swift中从dataTaskWithURL获得进展？
NSURLSession.sharedSession().dataTaskWithURL(...)
我需要在下载数据时显示进度条。
答案 0 :(得分：31)
您可以使用此代码显示带有代理功能的进度条的下载过程。
import UIKit
class ViewController: UIViewController,NSURLSessionDelegate,NSURLSessionDataDelegate{
@IBOutlet weak var progress: UIProgressView!
var buffer:NSMutableData = NSMutableData()
var session:NSURLSession?
var dataTask:NSURLSessionDataTask?
let url = NSURL(string:"http://i.stack.imgur.com/b8zkg.png" )!
var expectedContentLength = 0
override func viewDidLoad() {
super.viewDidLoad()
progress.progress = 0.0
let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
let manqueue = NSOperationQueue.mainQueue()
session = NSURLSession(configuration: configuration, delegate:self, delegateQueue: manqueue)
dataTask = session?.dataTaskWithRequest(NSURLRequest(URL: url))
dataTask?.resume()
// Do any additional setup after loading the view, typically from a nib.
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveResponse response: NSURLResponse, completionHandler: (NSURLSessionResponseDisposition) -> Void) {
//here you can get full lenth of your content
expectedContentLength = Int(response.expectedContentLength)
println(expectedContentLength)
completionHandler(NSURLSessionResponseDisposition.Allow)
}
func URLSession(session: NSURLSession, dataTask: NSURLSessionDataTask, didReceiveData data: NSData) {
buffer.appendData(data)
let percentageDownloaded = Float(buffer.length) / Float(expectedContentLength)
progress.progress = percentageDownloaded
}
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?) {
//use buffer here.Download is done
progress.progress = 1.0 // download 100% complete
}
}
答案 1 :(得分：16)
更新 Swift4 ：
支持执行多个同时操作。
档案：DownloadService.swift。继续引用URLSession并跟踪执行任务。
final class DownloadService: NSObject {
private var session: URLSession!
private var downloadTasks = [GenericDownloadTask]()
public static let shared = DownloadService()
private override init() {
super.init()
let configuration = URLSessionConfiguration.default
session = URLSession(configuration: configuration,
delegate: self, delegateQueue: nil)
}
func download(request: URLRequest) -> DownloadTask {
let task = session.dataTask(with: request)
let downloadTask = GenericDownloadTask(task: task)
downloadTasks.append(downloadTask)
return downloadTask
}
}
extension DownloadService: URLSessionDataDelegate {
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse,
completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
guard let task = downloadTasks.first(where: { $0.task == dataTask }) else {
completionHandler(.cancel)
return
}
task.expectedContentLength = response.expectedContentLength
completionHandler(.allow)
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
guard let task = downloadTasks.first(where: { $0.task == dataTask }) else {
return
}
task.buffer.append(data)
let percentageDownloaded = Double(task.buffer.count) / Double(task.expectedContentLength)
DispatchQueue.main.async {
task.progressHandler?(percentageDownloaded)
}
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
guard let index = downloadTasks.index(where: { $0.task == task }) else {
return
}
let task = downloadTasks.remove(at: index)
DispatchQueue.main.async {
if let e = error {
task.completionHandler?(.failure(e))
} else {
task.completionHandler?(.success(task.buffer))
}
}
}
}
档案：DownloadTask.swift。轻量级界面只是为了隐藏具体的实现。
protocol DownloadTask {
var completionHandler: ResultType<Data>.Completion? { get set }
var progressHandler: ((Double) -> Void)? { get set }
func resume()
func suspend()
func cancel()
}
档案：GenericDownloadTask.swift。 DownloadTask接口的具体实现。
class GenericDownloadTask {
var completionHandler: ResultType<Data>.Completion?
var progressHandler: ((Double) -> Void)?
private(set) var task: URLSessionDataTask
var expectedContentLength: Int64 = 0
var buffer = Data()
init(task: URLSessionDataTask) {
self.task = task
}
deinit {
print("Deinit: \(task.originalRequest?.url?.absoluteString ?? "")")
}
}
extension GenericDownloadTask: DownloadTask {
func resume() {
task.resume()
}
func suspend() {
task.suspend()
}
func cancel() {
task.cancel()
}
}
档案：ResultType.swift。可重复使用的类型以保持结果或错误。
public enum ResultType<T> {
public typealias Completion = (ResultType<T>) -> Void
case success(T)
case failure(Swift.Error)
}
用法：示例如何运行two download tasks in parallel（macOS App）：
class ViewController: NSViewController {
@IBOutlet fileprivate weak var loadImageButton1: NSButton!
@IBOutlet fileprivate weak var loadProgressIndicator1: NSProgressIndicator!
@IBOutlet fileprivate weak var imageView1: NSImageView!
@IBOutlet fileprivate weak var loadImageButton2: NSButton!
@IBOutlet fileprivate weak var loadProgressIndicator2: NSProgressIndicator!
@IBOutlet fileprivate weak var imageView2: NSImageView!
fileprivate var downloadTask1: DownloadTask?
fileprivate var downloadTask2: DownloadTask?
override func viewDidLoad() {
super.viewDidLoad()
loadImageButton1.target = self
loadImageButton1.action = #selector(startDownload1(_:))
loadImageButton2.target = self
loadImageButton2.action = #selector(startDownload2(_:))
}
}
extension ViewController {
@objc fileprivate func startDownload1(_ button: NSButton) {
let url = URL(string: "http://localhost:8001/?imageID=01&tilestamp=\(Date.timeIntervalSinceReferenceDate)")!
let request = URLRequest(url: url, cachePolicy: .reloadIgnoringLocalCacheData, timeoutInterval: 30)
downloadTask1 = DownloadService.shared.download(request: request)
downloadTask1?.completionHandler = { [weak self] in
switch $0 {
case .failure(let error):
print(error)
case .success(let data):
print("Number of bytes: \(data.count)")
self?.imageView1.image = NSImage(data: data)
}
self?.downloadTask1 = nil
self?.loadImageButton1.isEnabled = true
}
downloadTask1?.progressHandler = { [weak self] in
print("Task1: \($0)")
self?.loadProgressIndicator1.doubleValue = $0
}
loadImageButton1.isEnabled = false
imageView1.image = nil
loadProgressIndicator1.doubleValue = 0
downloadTask1?.resume()
}
@objc fileprivate func startDownload2(_ button: NSButton) {
let url = URL(string: "http://localhost:8002/?imageID=02&tilestamp=\(Date.timeIntervalSinceReferenceDate)")!
let request = URLRequest(url: url, cachePolicy: .reloadIgnoringLocalCacheData, timeoutInterval: 30)
downloadTask2 = DownloadService.shared.download(request: request)
downloadTask2?.completionHandler = { [weak self] in
switch $0 {
case .failure(let error):
print(error)
case .success(let data):
print("Number of bytes: \(data.count)")
self?.imageView2.image = NSImage(data: data)
}
self?.downloadTask2 = nil
self?.loadImageButton2.isEnabled = true
}
downloadTask2?.progressHandler = { [weak self] in
print("Task2: \($0)")
self?.loadProgressIndicator2.doubleValue = $0
}
loadImageButton2.isEnabled = false
imageView2.image = nil
loadProgressIndicator2.doubleValue = 0
downloadTask2?.resume()
}
}
奖金1 。档案StartPHPWebServer.command。运行2内置PHP服务器以模拟同时下载的示例脚本。
#!/bin/bash
AWLScriptDirPath=$(cd "$(dirname "$0")"; pwd)
cd "$AWLScriptDirPath"
php -S localhost:8001 &
php -S localhost:8002 &
ps -afx | grep php
echo "Press ENTER to exit."
read
killall php
奖金2 。档案index.php。用于实现慢速下载的示例PHP脚本。
<?php
$imageID = $_REQUEST["imageID"];
$local_file = "Image-$imageID.jpg";
$download_rate = 20.5; // set the download rate limit (=> 20,5 kb/s)
if (file_exists($local_file) && is_file($local_file)) {
header('Cache-control: private');
header('Content-Type: image/jpeg');
header('Content-Length: '.filesize($local_file));
flush();
$file = fopen($local_file, "r");
while(!feof($file)) {
// send the current file part to the browser
print fread($file, round($download_rate * 1024));
flush(); // flush the content to the browser
usleep(0.25 * 1000000);
}
fclose($file);}
else {
die('Error: The file '.$local_file.' does not exist!');
}
?>
Misc：模拟2台PHP服务器的目录内容。
Image-01.jpg
Image-02.jpg
StartPHPWebServer.command
index.php
答案 2 :(得分：8)
您可以简单地观察progress对象的URLSessionDataTask属性。
import Foundation
import PlaygroundSupport
let page = PlaygroundPage.current
page.needsIndefiniteExecution = true
let url = URL(string: "https://source.unsplash.com/random/4000x4000")!
let task = URLSession.shared.dataTask(with: url) { _, _, _ in
page.finishExecution()
}
// Don't forget to invalidate the observation when you don't need it anymore.
let observation = task.progress.observe(\.fractionCompleted) { progress, _ in
print(progress.fractionCompleted)
}
task.resume()
答案 3 :(得分：2)
在类声明中
class AudioPlayerViewController: UIViewController, URLSessionDelegate, URLSessionDataDelegate, URLSessionDownloadDelegate{
var defaultSession: URLSession!
var downloadTask: URLSessionDownloadTask!
下载方法
defaultSession = Foundation.URLSession(configuration: .default, delegate: self, delegateQueue: nil)
downloadProgress.setProgress(0.0, animated: false)
downloadTask = defaultSession.downloadTask(with: audioUrl)
downloadTask.Resume()
并添加以下代表：
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
DispatchQueue.main.async {
self.downloadProgressBar.setProgress(Float(totalBytesWritten)/Float(totalBytesExpectedToWrite), animated: true)
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
DispatchQueue.main.async {
//DOWNLOAD SUCCESSFUL AND FILE PATH WILL BE IN URL.
}
}
答案 4 :(得分：0)
要下载数据，您需要设置NSURLSessionDownloadDelegate并实施URLSession(_:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:)
有一个很好的教程here但是在object-c。
答案 5 :(得分：0)
关于Dharmesh的工作，URLSessionDelegate和URLSessionDataDelegate委托方法进行了许多次要更改。以下是实现 Swift 4.2 兼容性的代码。
import UIKit
class ViewController: UIViewController, URLSessionDelegate, URLSessionDataDelegate {
// MARK: - Variables
// MARK: - IBOutlet
@IBOutlet weak var progress: UIProgressView!
// MARK: - IBAction
@IBAction func goTapped(_ sender: UIButton) {
let url = URL(string: "http://www.example.com/file.zip")!
fetchFile(url: url)
}
// MARK: - Life cycle
override func viewDidLoad() {
super.viewDidLoad()
}
func fetchFile(url: URL) {
progress.progress = 0.0
let configuration = URLSessionConfiguration.default
let mainQueue = OperationQueue.main
session = URLSession(configuration: configuration, delegate: self, delegateQueue: mainQueue)
dataTask = session?.dataTask(with: URLRequest(url: url))
dataTask?.resume()
}
var buffer: NSMutableData = NSMutableData()
var session: URLSession?
var dataTask: URLSessionDataTask?
var expectedContentLength = 0
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
buffer.append(data)
let percentageDownloaded = Float(buffer.length) / Float(expectedContentLength)
progress.progress = percentageDownloaded
}
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: (URLSession.ResponseDisposition) -> Void) {
expectedContentLength = Int(response.expectedContentLength)
completionHandler(URLSession.ResponseDisposition.allow)
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
progress.progress = 1.0
}
}