我刚开始学习苹果iOS的Swift编程，之前从安卓转过来。现在基本能读懂和操作Swift代码，并学习了一些iOS Swift编程中常用的类，但对于语法和其他方面仍有一些困惑。
我正在尝试下载文件，比如说从这个URL下载：
var url = "http://www.mywebsite.com/myfile.pdf"
在按钮点击时执行，可能还有可视化进度条
通过在stackoverflow上搜索，我偶然发现了Alamofire。我可能会尝试使用它，但我不确定这是否是我实现目标的最佳方法。
因此，我想问一下，在iOS7和iOS8中实现我的目标的选项是什么？还有，利弊分析将是非常好的！
没有使用 Alamofire 的示例下载器类：
class Downloader {
class func load(URL: NSURL) {
let sessionConfig = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: sessionConfig, delegate: nil, delegateQueue: nil)
let request = NSMutableURLRequest(URL: URL)
request.HTTPMethod = "GET"
let task = session.dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse!, error: NSError!) -> Void in
if (error == nil) {
// Success
let statusCode = (response as NSHTTPURLResponse).statusCode
println("Success: \(statusCode)")
// This is your file-variable:
// data
}
else {
// Failure
println("Failure: %@", error.localizedDescription);
}
})
task.resume()
}
}
以下是如何在您自己的代码中使用它：
class Foo {
func bar() {
if var URL = NSURL(string: "http://www.mywebsite.com/myfile.pdf") {
Downloader.load(URL)
}
}
}
Swift 3 版本
请注意，下载大文件时，请将其存储在磁盘上而非内存中。请参阅`downloadTask:
class Downloader {
class func load(url: URL, to localUrl: URL, completion: @escaping () -> ()) {
let sessionConfig = URLSessionConfiguration.default
let session = URLSession(configuration: sessionConfig)
let request = try! URLRequest(url: url, method: .get)
let task = session.downloadTask(with: request) { (tempLocalUrl, response, error) in
if let tempLocalUrl = tempLocalUrl, error == nil {
// Success
if let statusCode = (response as? HTTPURLResponse)?.statusCode {
print("Success: \(statusCode)")
}
do {
try FileManager.default.copyItem(at: tempLocalUrl, to: localUrl)
completion()
} catch (let writeError) {
print("error writing file \(localUrl) : \(writeError)")
}
} else {
print("Failure: %@", error?.localizedDescription);
}
}
task.resume()
}
}
如果有人仍然需要，这是Swift 4和Swift 5的版本
import Foundation
class FileDownloader {
static func loadFileSync(url: URL, completion: @escaping (String?, Error?) -> Void)
{
let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let destinationUrl = documentsUrl.appendingPathComponent(url.lastPathComponent)
if FileManager().fileExists(atPath: destinationUrl.path)
{
print("File already exists [\(destinationUrl.path)]")
completion(destinationUrl.path, nil)
}
else if let dataFromURL = NSData(contentsOf: url)
{
if dataFromURL.write(to: destinationUrl, atomically: true)
{
print("file saved [\(destinationUrl.path)]")
completion(destinationUrl.path, nil)
}
else
{
print("error saving file")
let error = NSError(domain:"Error saving file", code:1001, userInfo:nil)
completion(destinationUrl.path, error)
}
}
else
{
let error = NSError(domain:"Error downloading file", code:1002, userInfo:nil)
completion(destinationUrl.path, error)
}
}
static func loadFileAsync(url: URL, completion: @escaping (String?, Error?) -> Void)
{
let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let destinationUrl = documentsUrl.appendingPathComponent(url.lastPathComponent)
if FileManager().fileExists(atPath: destinationUrl.path)
{
print("File already exists [\(destinationUrl.path)]")
completion(destinationUrl.path, nil)
}
else
{
let session = URLSession(configuration: URLSessionConfiguration.default, delegate: nil, delegateQueue: nil)
var request = URLRequest(url: url)
request.httpMethod = "GET"
let task = session.dataTask(with: request, completionHandler:
{
data, response, error in
if error == nil
{
if let response = response as? HTTPURLResponse
{
if response.statusCode == 200
{
if let data = data
{
if let _ = try? data.write(to: destinationUrl, options: Data.WritingOptions.atomic)
{
completion(destinationUrl.path, error)
}
else
{
completion(destinationUrl.path, error)
}
}
else
{
completion(destinationUrl.path, error)
}
}
}
}
else
{
completion(destinationUrl.path, error)
}
})
task.resume()
}
}
}
这是如何调用此方法的步骤：
let url = URL(string: "http://www.filedownloader.com/mydemofile.pdf")
FileDownloader.loadFileAsync(url: url!) { (path, error) in
print("PDF File downloaded to : \(path!)")
}
这里有一个例子展示了如何进行同步和异步操作。
import Foundation
class HttpDownloader {
class func loadFileSync(url: NSURL, completion:(path:String, error:NSError!) -> Void) {
let documentsUrl = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as! NSURL
let destinationUrl = documentsUrl.URLByAppendingPathComponent(url.lastPathComponent!)
if NSFileManager().fileExistsAtPath(destinationUrl.path!) {
println("file already exists [\(destinationUrl.path!)]")
completion(path: destinationUrl.path!, error:nil)
} else if let dataFromURL = NSData(contentsOfURL: url){
if dataFromURL.writeToURL(destinationUrl, atomically: true) {
println("file saved [\(destinationUrl.path!)]")
completion(path: destinationUrl.path!, error:nil)
} else {
println("error saving file")
let error = NSError(domain:"Error saving file", code:1001, userInfo:nil)
completion(path: destinationUrl.path!, error:error)
}
} else {
let error = NSError(domain:"Error downloading file", code:1002, userInfo:nil)
completion(path: destinationUrl.path!, error:error)
}
}
class func loadFileAsync(url: NSURL, completion:(path:String, error:NSError!) -> Void) {
let documentsUrl = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as! NSURL
let destinationUrl = documentsUrl.URLByAppendingPathComponent(url.lastPathComponent!)
if NSFileManager().fileExistsAtPath(destinationUrl.path!) {
println("file already exists [\(destinationUrl.path!)]")
completion(path: destinationUrl.path!, error:nil)
} else {
let sessionConfig = NSURLSessionConfiguration.defaultSessionConfiguration()
let session = NSURLSession(configuration: sessionConfig, delegate: nil, delegateQueue: nil)
let request = NSMutableURLRequest(URL: url)
request.HTTPMethod = "GET"
let task = session.dataTaskWithRequest(request, completionHandler: { (data: NSData!, response: NSURLResponse!, error: NSError!) -> Void in
if (error == nil) {
if let response = response as? NSHTTPURLResponse {
println("response=\(response)")
if response.statusCode == 200 {
if data.writeToURL(destinationUrl, atomically: true) {
println("file saved [\(destinationUrl.path!)]")
completion(path: destinationUrl.path!, error:error)
} else {
println("error saving file")
let error = NSError(domain:"Error saving file", code:1001, userInfo:nil)
completion(path: destinationUrl.path!, error:error)
}
}
}
}
else {
println("Failure: \(error.localizedDescription)");
completion(path: destinationUrl.path!, error:error)
}
})
task.resume()
}
}
}
以下是如何在您的代码中使用它：
let url = NSURL(string: "http://www.mywebsite.com/myfile.pdf")
HttpDownloader.loadFileAsync(url, completion:{(path:String, error:NSError!) in
println("pdf downloaded to: \(path)")
})
如果您需要将纯文本文件下载到 String，您可以使用这种简单的方式，Swift 5：
如果你只需要将文本文件下载到String中，你可以使用这种简单方式，Swift 5：
let list = try? String(contentsOf: URL(string: "https://example.com/file.txt")!)
如果您需要非可选结果或错误处理：
do {
let list = try String(contentsOf: URL(string: "https://example.com/file.txt")!)
}
catch {
// Handle error here
}
您应该知道网络操作可能需要一些时间，为了防止它在主线程中运行并锁定您的用户界面，您可能希望异步执行代码，例如：
DispatchQueue.global().async {
let list = try? String(contentsOf: URL(string: "https://example.com/file.txt")!)
}
只要您的应用程序在前台，Devran和djunod的解决方案都可以正常工作。但是，如果您在下载期间切换到另一个应用程序，则会失败。我的文件大小约为10 MB，下载需要一些时间。因此，我需要我的下载功能即使应用程序进入后台也能正常工作。
请注意，我已经在“Capabilities”中打开了“Background Modes / Background Fetch”。
由于不支持completionhandler，所以该解决方案未封装。很抱歉。
--Swift 2.3--
import Foundation
class Downloader : NSObject, NSURLSessionDownloadDelegate
{
var url : NSURL?
// will be used to do whatever is needed once download is complete
var yourOwnObject : NSObject?
init(yourOwnObject : NSObject)
{
self.yourOwnObject = yourOwnObject
}
//is called once the download is complete
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didFinishDownloadingToURL location: NSURL)
{
//copy downloaded data to your documents directory with same names as source file
let documentsUrl = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first
let destinationUrl = documentsUrl!.URLByAppendingPathComponent(url!.lastPathComponent!)
let dataFromURL = NSData(contentsOfURL: location)
dataFromURL?.writeToURL(destinationUrl, atomically: true)
//now it is time to do what is needed to be done after the download
yourOwnObject!.callWhatIsNeeded()
}
//this is to track progress
func URLSession(session: NSURLSession, downloadTask: NSURLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64)
{
}
// if there is an error during download this will be called
func URLSession(session: NSURLSession, task: NSURLSessionTask, didCompleteWithError error: NSError?)
{
if(error != nil)
{
//handle the error
print("Download completed with error: \(error!.localizedDescription)");
}
}
//method to be called to download
func download(url: NSURL)
{
self.url = url
//download identifier can be customized. I used the "ulr.absoluteString"
let sessionConfig = NSURLSessionConfiguration.backgroundSessionConfigurationWithIdentifier(url.absoluteString)
let session = NSURLSession(configuration: sessionConfig, delegate: self, delegateQueue: nil)
let task = session.downloadTaskWithURL(url)
task.resume()
}
}
这里是如何调用 --Swift 2.3-- 的方法
let url = NSURL(string: "http://company.com/file.txt")
Downloader(yourOwnObject).download(url!)
--Swift 3--
class Downloader : NSObject, URLSessionDownloadDelegate {
var url : URL?
// will be used to do whatever is needed once download is complete
var yourOwnObject : NSObject?
init(_ yourOwnObject : NSObject)
{
self.yourOwnObject = yourOwnObject
}
//is called once the download is complete
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL)
{
//copy downloaded data to your documents directory with same names as source file
let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first
let destinationUrl = documentsUrl!.appendingPathComponent(url!.lastPathComponent)
let dataFromURL = NSData(contentsOf: location)
dataFromURL?.write(to: destinationUrl, atomically: true)
//now it is time to do what is needed to be done after the download
yourOwnObject!.callWhatIsNeeded()
}
//this is to track progress
private func URLSession(session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64)
{
}
// if there is an error during download this will be called
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?)
{
if(error != nil)
{
//handle the error
print("Download completed with error: \(error!.localizedDescription)");
}
}
//method to be called to download
func download(url: URL)
{
self.url = url
//download identifier can be customized. I used the "ulr.absoluteString"
let sessionConfig = URLSessionConfiguration.background(withIdentifier: url.absoluteString)
let session = Foundation.URLSession(configuration: sessionConfig, delegate: self, delegateQueue: nil)
let task = session.downloadTask(with: url)
task.resume()
}}
以下是如何在Swift 3中调用的方法：
let url = URL(string: "http://company.com/file.txt")
Downloader(yourOwnObject).download(url!)
这里是 Swift 4 版本：
static func loadFileAsync(url: URL, completion: @escaping (String?, Error?) -> Void)
{
let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let destinationUrl = documentsUrl.appendingPathComponent(url.lastPathComponent)
if FileManager().fileExists(atPath: destinationUrl.path)
{
completion(destinationUrl.path, nil)
}
else
{
let session = URLSession(configuration: URLSessionConfiguration.default, delegate: nil, delegateQueue: nil)
var request = URLRequest(url: url)
request.httpMethod = "GET"
let task = session.dataTask(with: request, completionHandler:
{
data, response, error in
if error == nil
{
if let response = response as? HTTPURLResponse
{
if response.statusCode == 200
{
if let data = data
{
if let _ = try? data.write(to: destinationUrl, options: Data.WritingOptions.atomic)
{
completion(destinationUrl.path, error)
}
else
{
completion(destinationUrl.path, error)
}
}
else
{
completion(destinationUrl.path, error)
}
}
}
}
else
{
completion(destinationUrl.path, error)
}
})
task.resume()
}
}
Swift 3
你想逐字节地下载文件并在进度视图中显示，因此你可以尝试这段代码。
import UIKit
class ViewController: UIViewController,URLSessionDownloadDelegate,UIDocumentInteractionControllerDelegate {
@IBOutlet weak var img: UIImageView!
@IBOutlet weak var btndown: UIButton!
var urlLink: URL!
var defaultSession: URLSession!
var downloadTask: URLSessionDownloadTask!
//var backgroundSession: URLSession!
@IBOutlet weak var progress: UIProgressView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
let backgroundSessionConfiguration = URLSessionConfiguration.background(withIdentifier: "backgroundSession")
defaultSession = Foundation.URLSession(configuration: backgroundSessionConfiguration, delegate: self, delegateQueue: OperationQueue.main)
progress.setProgress(0.0, animated: false)
}
func startDownloading () {
let url = URL(string: "http://publications.gbdirect.co.uk/c_book/thecbook.pdf")!
downloadTask = defaultSession.downloadTask(with: url)
downloadTask.resume()
}
@IBAction func btndown(_ sender: UIButton) {
startDownloading()
}
func showFileWithPath(path: String){
let isFileFound:Bool? = FileManager.default.fileExists(atPath: path)
if isFileFound == true{
let viewer = UIDocumentInteractionController(url: URL(fileURLWithPath: path))
viewer.delegate = self
viewer.presentPreview(animated: true)
}
}
// MARK:- URLSessionDownloadDelegate
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
print(downloadTask)
print("File download succesfully")
let path = NSSearchPathForDirectoriesInDomains(FileManager.SearchPathDirectory.documentDirectory, FileManager.SearchPathDomainMask.userDomainMask, true)
let documentDirectoryPath:String = path[0]
let fileManager = FileManager()
let destinationURLForFile = URL(fileURLWithPath: documentDirectoryPath.appendingFormat("/file.pdf"))
if fileManager.fileExists(atPath: destinationURLForFile.path){
showFileWithPath(path: destinationURLForFile.path)
print(destinationURLForFile.path)
}
else{
do {
try fileManager.moveItem(at: location, to: destinationURLForFile)
// show file
showFileWithPath(path: destinationURLForFile.path)
}catch{
print("An error occurred while moving file to destination url")
}
}
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
progress.setProgress(Float(totalBytesWritten)/Float(totalBytesExpectedToWrite), animated: true)
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
downloadTask = nil
progress.setProgress(0.0, animated: true)
if (error != nil) {
print("didCompleteWithError \(error?.localizedDescription ?? "no value")")
}
else {
print("The task finished successfully")
}
}
func documentInteractionControllerViewControllerForPreview(_ controller: UIDocumentInteractionController) -> UIViewController
{
return self
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}
使用此代码，您可以自动将下载的文件存储在应用程序的文档目录中
此代码百分之百有效
是的，你可以通过以下代码非常容易地从远程 URL 下载文件。 这段代码对我来说运行得很好。
func DownlondFromUrl(){
// Create destination URL
let documentsUrl:URL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first as URL!
let destinationFileUrl = documentsUrl.appendingPathComponent("downloadedFile.jpg")
//Create URL to the source file you want to download
let fileURL = URL(string: "https://s3.amazonaws.com/learn-swift/IMG_0001.JPG")
let sessionConfig = URLSessionConfiguration.default
let session = URLSession(configuration: sessionConfig)
let request = URLRequest(url:fileURL!)
let task = session.downloadTask(with: request) { (tempLocalUrl, response, error) in
if let tempLocalUrl = tempLocalUrl, error == nil {
// Success
if let statusCode = (response as? HTTPURLResponse)?.statusCode {
print("Successfully downloaded. Status code: \(statusCode)")
}
do {
try FileManager.default.copyItem(at: tempLocalUrl, to: destinationFileUrl)
} catch (let writeError) {
print("Error creating a file \(destinationFileUrl) : \(writeError)")
}
} else {
print("Error took place while downloading a file. Error description: %@", error?.localizedDescription);
}
}
task.resume()
}
在Swift 5中下载文件时，可以使用进度报告并封装到一个易于复制粘贴的协议访问类中：
protocol FileDownloadingDelegate: class {
func updateDownloadProgressWith(progress: Float)
func downloadFinished(localFilePath: URL)
func downloadFailed(withError error: Error)
}
class FilesDownloader: NSObject, URLSessionDownloadDelegate {
private weak var delegate: FileDownloadingDelegate?
func download(from url: URL, delegate: FileDownloadingDelegate) {
self.delegate = delegate
let sessionConfig = URLSessionConfiguration.background(withIdentifier: url.absoluteString) // use this identifier to resume download after app restart
let session = Foundation.URLSession(configuration: sessionConfig, delegate: self, delegateQueue: nil)
let task = session.downloadTask(with: url)
task.resume()
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
DispatchQueue.main.async { self.delegate?.downloadFinished(localFilePath: location) }
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
DispatchQueue.main.async { self.delegate?.updateDownloadProgressWith(progress: Float(totalBytesWritten)/Float(totalBytesExpectedToWrite)) }
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
guard let theError = error else { assertionFailure("something weird happened here"); return }
DispatchQueue.main.async { self.delegate?.downloadFailed(withError: theError) }
}
}
如何使用：
class MyViewController: UIViewController {
private lazy var downloader = FilesDownloader()
func downloadFile(from url: URL) {
downloader.download(from: url, delegate: self)
}
}
extension MyViewController: FileDownloadingDelegate {
func updateDownloadProgressWith(progress: Float) {
// self.downloadProgressView.setProgress(progress, animated: true)
}
func downloadFinished(tempFilePath: URL) {
print("downloaded to \(tempFilePath)")
// resave the file into your desired place using
// let dataFromURL = NSData(contentsOf: location)
// dataFromURL?.write(to: yourDesiredFileUrl, atomically: true)
}
func downloadFailed(withError error: Error) {
// handle the error
}
}
尝试了一些上述建议（包括Swift版本...），但都没有成功，最终我使用了官方文档：https://developer.apple.com/documentation/foundation/url_loading_system/downloading_files_from_websites
let downloadTask = URLSession.shared.downloadTask(with: url) {
urlOrNil, responseOrNil, errorOrNil in
// check for and handle errors:
// * errorOrNil should be nil
// * responseOrNil should be an HTTPURLResponse with statusCode in 200..<299
guard let fileURL = urlOrNil else { return }
do {
let documentsURL = try
FileManager.default.url(for: .documentDirectory,
in: .userDomainMask,
appropriateFor: nil,
create: false)
let savedURL = documentsURL.appendingPathComponent(fileURL.lastPathComponent)
try FileManager.default.moveItem(at: fileURL, to: savedURL)
} catch {
print ("file error: \(error)")
}
}
downloadTask.resume()
data包含整个二进制PDF文件。要返回data的内容，只需写入println(data)。如果想学习如何在iOS上保存文件，请看：https://github.com/sketchytech/FileSave （也有Swift版本）。 - Devran Cosmo Uenal