如何在swift中下载文件？

Question

我刚刚开始学习来自android的iOS苹果swift编程.我现在基本上可以阅读和操作swift代码,还学习了一些在iOS swift编程中使用的常见类,但仍然对语法和一切都有些混淆.

我正在尝试下载文件.就像,让我们说来自这个URL

var url = "http://www.mywebsite.com/myfile.pdf"

在按钮单击中.也许还有视觉进步

通过在stackoverflow中搜索,我偶然发现了Alamofire.我可能会尝试但是我不确定这是否是我做这件事的最佳方式.

所以,我想问一下如何以及我的选择(iOS7和iOS8)实现我的目标.此外,利弊会很棒!

Answer 1

没有Alamofire的示例下载程序类:

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()
    }
}

这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

另请注意,要在磁盘上下载大文件,而不是在内存中.看`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()
    }
}

Answer 2

Swift 4和Swift 5版本，如果还有人需要的话

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()
        }
    }
}

以下是调用此方法的方法：-

let url = URL(string: "http://www.filedownloader.com/mydemofile.pdf")
FileDownloader.loadFileAsync(url: url!) { (path, error) in
    print("PDF File downloaded to : \(path!)")
}

Answer 3

这是一个显示如何进行同步和异步的示例.

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()
        }
    }
}

以下是在代码中使用它的方法:

let url = NSURL(string: "http://www.mywebsite.com/myfile.pdf") 
HttpDownloader.loadFileAsync(url, completion:{(path:String, error:NSError!) in
                println("pdf downloaded to: \(path)")
            })

Answer 4

只要您的应用程序处于前台,Devran和djunod的解决方案就可以正常运行.如果在下载过程中切换到其他应用程序,则会失败.我的文件大小约为10 MB,下载需要一些时间.因此,即使应用程序进入后台,我也需要我的下载功能.

请注意,我在"Capabilities"处打开了"Background Modes/Background Fetch".

由于不支持completionhandler,因此解决方案未封装.对于那个很抱歉.

--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()
    }
}

以下是如何打电话给--Swift 2.3--

    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()
}}

以下是如何打电话给--Swift 3--

    let url = URL(string: "http://company.com/file.txt")
    Downloader(yourOwnObject).download(url!)

Answer 5

如果你只需要下载文本文件String就可以使用这个简单的方法,Swift 3:

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,以防止它在主线程中运行并锁定您的UI,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")!)
}

Answer 6

这是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()
    }
}

Answer 7

迅捷3

您想一口气下载文件并在进度视图中显示，以便尝试此代码

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，您要在应用程序的文档目录中自动下载文件存储

此代码100％工作

Answer 8

是的，您可以使用此代码轻松地从远程URL下载文件。该代码对我来说很好。

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()
}

Answer 9

iOS 13 斯威夫特 5、5.1

@IBAction func btnDownload(_ sender: Any) {
    
    // file location to save download file
    let destination: DownloadRequest.DownloadFileDestination = { _, _ in
        var documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
        documentsURL.appendPathComponent(statementPDF)
        return (documentsURL, [.removePreviousFile])
    }
    
    // Alamofire to download file
    Alamofire.download("http://pdf_url", to: destination).responseData { response in
        hideLoader()
        switch response.result {
        case .success:
            // write something here
            if response.destinationURL != nil {
                showAlertMessage(titleStr: APPNAME, messageStr: "File Saved in Documents!")
                
            }
        case .failure:
            showAlertMessage(titleStr: APPNAME, messageStr: response.result.error.debugDescription)
        }
    }
}

请将这些权限添加到 info.plist，以便您可以在中检查下载文件Document Directory

<key>UIFileSharingEnabled</key>
<true/>
<key>LSSupportsOpeningDocumentsInPlace</key>
<true/>

Answer 10

在尝试了上述一些建议但没有成功（Swift版本...）之后，我最终使用了官方文档：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()

Answer 11

在 Swift 5 中下载带有进度报告的文件，封装到复制粘贴友好的协议访问类中：

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) }
    }

}

如何使用它：

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
    }
}