[英]Downloading & Uploading Data From URL Swift Asynchronously
I have an array of 5 links which contain either jpg
or mov
files. 我有5个链接数组,其中包含
jpg
或mov
文件。 I want to download them into my iOS Swift app. 我想将它们下载到我的iOS Swift应用中。 I use the following code.
我使用以下代码。
var index = 0
while (index < myLinks.count) {
if (myLinks[index].resource_type == "image") {
let stringURL = "http://www.blablabla" + ".jpg"
let url = NSURL(string : stringURL)
getDataFromUrl(url!) { (data, response, error) in
guard let data = data where error == nil else { return }
print(response?.suggestedFilename ?? url!.lastPathComponent ?? "")
print("Download Finished")
myLinks[index].image = UIImage(data: data)
}
}
else if (myLinks[index].resource_type == "video") {
let stringURL = "http://www.blablabla" + ".mov"
let url = NSURL(string : stringURL)
getDataFromUrl(url!) { (data, response, error) in
guard let data = data where error == nil else { return }
print(response?.suggestedFilename ?? url!.lastPathComponent ?? "")
print("Download Finished")
dispatch_async(dispatch_get_main_queue(), {
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
let documentsDirectory : NSString = paths[0]
let appFile = documentsDirectory.stringByAppendingPathComponent(myLinks[index].id! + ".m4v")
do {
try data.writeToFile(appFile, options: .AtomicWrite)
myLinks[index].videoURL = NSURL(fileURLWithPath: appFile)
}
catch _ {
print("error saving video")
}
})
}
}
index = index + 1
}
func getDataFromUrl(url: NSURL, completion: ((data: NSData?, response: NSURLResponse?, error: NSError? ) -> Void)) {
NSURLSession.sharedSession().dataTaskWithURL(url) {
(data, response, error) in
completion(data: data, response: response, error: error)
}.resume()
}
Now the only problem is that, after downloading these resources, I want to display them to the user in a form of slideshow, hence I can only proceed knowing that all 5 downloads have been completed. 现在唯一的问题是,在下载这些资源之后,我想以幻灯片形式向用户显示它们,因此,只有知道所有5个下载都已完成,我才能继续进行。 The problem with the code above is that since the
getDataFromUrl
function is executed asynchronously, this while loop will finish executing before all of the content has actually been downloaded. 上面的代码的问题在于,由于
getDataFromUrl
函数是异步执行的,因此while循环将在所有内容实际下载之前完成执行。
EDIT 编辑
Here is a code adapting the accepted answer to uploading as well. 这也是使接受的答案也适合上传的代码。 The problem is that when more than one value is in the queue, only the first task gets executed and then nothing happens.
问题在于,当队列中有多个值时,只有第一个任务被执行,然后什么也没有发生。
var uploadQueue:[UploadMessage]?
let session = NSURLSession.sharedSession()
let lockQueue = dispatch_queue_create("com.dsdevelop.lockQueue", nil)
func getRemainingActiveUploads() -> Int {
return (self.uploadQueue != nil) ? self.uploadQueue!.count : 0
}
func removeMessageFromUploadQueue(messageToBeRemoved : UploadMessage) {
if (uploadQueue != nil) {
dispatch_sync(lockQueue) {
self.uploadQueue = self.uploadQueue?.filter({$0.date!.compare(messageToBeRemoved.date!) == NSComparisonResult.OrderedSame})
}
}
}
var uploadTimer : NSTimer?
func finishedUploading() {
uploadTimer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: #selector(uploadAllLinks), userInfo: nil, repeats: false)
if (needToRefetch) {
needToRefetch = false
newMessageReceived()
}
}
func uploadAllLinks()
{
print("uploading test")
uploadTimer?.invalidate()
uploadTimer = nil
// suspending queue so they don't all finish before we can show it
session.delegateQueue.suspended = true
session.delegateQueue.maxConcurrentOperationCount = 1
let myUrl = NSURL(string: "http://****")
// create tasks
if (uploadQueue != nil) {
if (uploadQueue?.count > 0) {
for message in uploadQueue!
{
let request = NSMutableURLRequest(URL:myUrl!)
request.HTTPMethod = "POST"
request.timeoutInterval = 10
request.HTTPShouldHandleCookies=false
var postString = "sender=" + message.sender!
request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding);
let dltask = session.dataTaskWithRequest(request, completionHandler: { (data, response, error) in
if data != nil
{
do {
let jsonArray = try NSJSONSerialization.JSONObjectWithData(data_fixed!, options:[])
dispatch_async(dispatch_get_main_queue(), {
if let errorToken = jsonArray["error"] as! Bool? {
if !errorToken {
self.uploadQueue = self.uploadQueue!.filter({$0.date!.compare(message.date!) != NSComparisonResult.OrderedSame})
let remaining = self.getRemainingActiveUploads()
print("Downloaded. Remaining: \(remaining)")
if (remaining == 0) {
self.finishedUploading()
}
}
else {
let remaining = self.getRemainingActiveUploads()
print("Downloaded. Remaining: \(remaining)")
if (remaining == 0) {
self.finishedUploading()
}
}
}
else {
let remaining = self.getRemainingActiveUploads()
print("Downloaded. Remaining: \(remaining)")
if (remaining == 0) {
self.finishedUploading()
}
}
})
}
catch {
print("Error: \(error)")
}
}
})
print("Queuing task \(dltask)")
dltask.resume()
}
session.delegateQueue.suspended = false
}
else {
finishedUploading()
}
// resuming queue so all tasks run
}
}
Using the built in abilities of NSURLSession
and its underlying NSOperationQueue
you can do this easily enough. 使用
NSURLSession
及其基础的NSOperationQueue
的内置功能,您可以很容易地做到这一点。
import UIKit
class ViewController: UIViewController {
let MyDownloadsCompleteNotification:String = "MyDownloadsCompleteNotification"
var myLinks:[NSURL]?
var downloadQueue:[NSURL]?
let session = NSURLSession.sharedSession()
let lockQueue = dispatch_queue_create("com.dsdevelop.lockQueue", nil)
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
myLinks = [ NSURL(string: "https://pbs.twimg.com/profile_images/447374371917922304/P4BzupWu.jpeg")!,
NSURL(string: "http://www.telegraph.co.uk/content/dam/pets/2016/03/18/bunny-large_trans++qVzuuqpFlyLIwiB6NTmJwfSVWeZ_vEN7c6bHu2jJnT8.jpg")!,
NSURL(string: "http://4.bp.blogspot.com/-HTvSYzA-pO4/UgQb4Zh_u0I/AAAAAAAAEuI/XwhtogT_1tA/s1600/3+cute2.jpg")!,
NSURL(string: "http://cdn.shopify.com/s/files/1/0224/1915/files/bunny.jpg?22110")!,
NSURL(string: "http://vignette1.wikia.nocookie.net/hare/images/1/1f/Bunnies-bunny-rabbits-16437969-1280-800.jpg/revision/latest?cb=20130831183111")!
]
// Register to know when all downloads are done
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(allDownloadsComplete), name: MyDownloadsCompleteNotification, object: nil)
downloadAllLinks(myLinks!)
}
func allDownloadsComplete(n:NSNotification)
{
print("Awesome all downloads are done!")
}
func getRemainingActiveDownloads() -> Int
{
return (self.downloadQueue != nil) ? self.downloadQueue!.count : 0
}
func removeUrlFromDownloadQueue(url:NSURL)
{
if self.downloadQueue != nil
{
dispatch_sync(lockQueue) {
self.downloadQueue = self.downloadQueue!.filter({$0.absoluteString == url.absoluteString})
}
}
}
func downloadAllLinks(links:[NSURL])
{
// suspending queue so they don't all finish before we can show it
session.delegateQueue.suspended = true
session.delegateQueue.maxConcurrentOperationCount = 1
downloadQueue = links
// create tasks
for link in links
{
let dltask = session.downloadTaskWithURL(link, completionHandler: { (url, response, error) in
if let urlString = response?.URL?.absoluteString
{
self.downloadQueue = self.downloadQueue!.filter({$0.absoluteString != urlString})
let remaining = self.getRemainingActiveDownloads()
print("Downloaded. Remaining: \(remaining)")
if (remaining == 0)
{
NSNotificationCenter.defaultCenter().postNotificationName(self.MyDownloadsCompleteNotification, object: nil)
}
}
})
print("Queuing task \(dltask)")
dltask.resume()
}
// resuming queue so all tasks run
session.delegateQueue.suspended = false
}
}
You could create a timer to check whether all 5 resources have been completely downloaded. 您可以创建一个计时器来检查所有5个资源是否都已完全下载。 Set the interval to 1ms and you will know immediately once all 5 are done.
将间隔设置为1ms,一旦完成所有5个操作,您将立即知道。
You should add a var downloadsCompletedCounter = 0
and in your completion handler you should increment this counter: 您应该添加一个
var downloadsCompletedCounter = 0
并在完成处理程序中增加此计数器:
self.downloadsCompletedCounter =+ 1
Use this in the block of dispatch_async(dispatch_get_main_queue()
to avoid multithreading issues. 在
dispatch_async(dispatch_get_main_queue()
的块中使用此函数,以避免多线程问题。
You can also implement a property observer for downloadsCompletedCounter so that you know exactly when the downloads complete: 您还可以为downloadsCompletedCounter实现一个属性观察器,以便确切知道下载何时完成:
var downloadsCompletedCounter = 0 {
didSet{
if downloadsCompletedCounter == 4 {
print("Downloads completed")
// call the function you want to execute after downloads complete
}
}
}
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