使用 Swift 从服务器下载文件

Question

您好，我有一大堆 .mp3 文件，我想与 NSFileManager 一起使用并存储在文档文件夹中。有没有办法可以在线下载 .mp3 文件，然后将其保存到文档文件夹中？这是我用于本地文件的内容。

let filemanager = NSFileManager.defaultManager()
let documentsPath : AnyObject = NSSearchPathForDirectoriesInDomains(.DocumentDirectory,.UserDomainMask,true)[0]
let destinationPath:NSString = documentsPath.stringByAppendingString("/Attention.mp3")

if (!filemanager.fileExistsAtPath(destinationPath)) {
  var theError: NSError?
  let fileForCopy = NSBundle.mainBundle().pathForResource("Attention",ofType:"mp3")
  filemanager.copyItemAtPath(fileForCopy!,toPath:destinationPath, error: &theError)

  if (theError == nil) {
    println("The music files has been saved.")
  } else {
    println("Error")
  }
} else {
  println("The files already exist")
}

Answer 1

我发现@leo-dabus 可以立即使用，但必须根据我的需要进行两个小改动。这可能对其他人有帮助。

更改 #1：处理包含在路径扩展中的文件名

    if let fileName = fileName {
        if fileName.hasSuffix(self.pathExtension) {
            destination = directory
                .appendingPathComponent(fileName)
        } else {
            destination = directory
                .appendingPathComponent(fileName)
                .appendingPathExtension(self.pathExtension)
        }
    } else {
        destination = directory
            .appendingPathComponent(lastPathComponent)
    }

更改 #2：如果目标文件存在，则生成唯一名称

例如生成File (2).txt 以避免覆盖File.txt，就像网络浏览器一样。

    if !overwrite {
        let pathExtension = destination.pathExtension
        let lastComponent = destination.deletingPathExtension().lastPathComponent
        var copyNumber = 2
        var attemptedURL = destination
        while FileManager.default.fileExists(atPath: attemptedURL.path) {
            attemptedURL = destination
                .deletingPathExtension()
                .deletingLastPathComponent()
                .appendingPathComponent("\(lastComponent) (\(copyNumber))")
                .appendingPathExtension(pathExtension)
            copyNumber += 1
        }
        destination = attemptedURL
    }

Answer 2

编辑/更新：Xcode 11.5 • Swift 5.2

import UIKit
import AVFoundation

class ViewController: UIViewController {
    var player: AVPlayer!
    override func viewDidLoad() {
        super.viewDidLoad()
        let alarm = URL(string: "https://www.ringtonemobi.com/storage/upload/user_id_1/iphone-5-alarm-2016-08-21-01-49-25.mp3")!
        do {
            try alarm.download(to: .documentDirectory) { url, error in
                guard let url = url else { return }
                self.player = AVPlayer(url: url)
                self.player.play()
            }
        } catch {
            print(error)
        }
    }
}

---

import Foundation
extension URL {
    func download(to directory: FileManager.SearchPathDirectory, using fileName: String? = nil, overwrite: Bool = false, completion: @escaping (URL?, Error?) -> Void) throws {
        let directory = try FileManager.default.url(for: directory, in: .userDomainMask, appropriateFor: nil, create: true)
        let destination: URL
        if let fileName = fileName {
            destination = directory
                .appendingPathComponent(fileName)
                .appendingPathExtension(self.pathExtension)
        } else {
            destination = directory
            .appendingPathComponent(lastPathComponent)
        }
        if !overwrite, FileManager.default.fileExists(atPath: destination.path) {
            completion(destination, nil)
            return
        }
        URLSession.shared.downloadTask(with: self) { location, _, error in
            guard let location = location else {
                completion(nil, error)
                return
            }
            do {
                if overwrite, FileManager.default.fileExists(atPath: destination.path) {
                    try FileManager.default.removeItem(at: destination)
                }
                try FileManager.default.moveItem(at: location, to: destination)
                completion(destination, nil)
            } catch {
                print(error)
            }
        }.resume()
    }
}

---

---

原答案

Xcode 8.3.2 • Swift 3.1

if let audioUrl = URL(string: "http://freetone.org/ring/stan/iPhone_5-Alarm.mp3") {
    // create your document folder url
    let documentsUrl = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
    // your destination file url
    let destination = documentsUrl.appendingPathComponent(audioUrl.lastPathComponent)
    print(destination)
    // check if it exists before downloading it
    if FileManager.default.fileExists(atPath: destination.path) {
        print("The file already exists at path")
    } else {
        //  if the file doesn't exist
        //  just download the data from your url
        URLSession.shared.downloadTask(with: audioUrl, completionHandler: { (location, response, error) in
            // after downloading your data you need to save it to your destination url
            guard
                let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
                let mimeType = response?.mimeType, mimeType.hasPrefix("audio"),
                let location = location, error == nil
                else { return }
            do {
                try FileManager.default.moveItem(at: location, to: destination)
                print("file saved")
            } catch {
                print(error)
            }
        }).resume()
    }
}

Answer 3

Xcode 10.1、Swift 4

我使用了上面来自@leo-dabus 的示例，但将代码分成了两个函数。我在这种方法中发现的一个缺陷是它没有处理文件已经下载的情况。

此示例将删除任何先前已下载的文件并写入最新版本。

/// Downloads a file asynchronously
func loadFileAsync(url: URL, completion: @escaping (Bool) -> Void) {

    // create your document folder url
    let documentsUrl = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)

    // your destination file url
    let destination = documentsUrl.appendingPathComponent(url.lastPathComponent)

    log.info(m: "downloading file from URL: \(url.absoluteString)")
    if FileManager().fileExists(atPath: destination.path) {
        print("The file already exists at path, deleting and replacing with latest")

        if FileManager().isDeletableFile(atPath: destination.path){
            do{
                try FileManager().removeItem(at: destination)
                print("previous file deleted")
                self.saveFile(url: url, destination: destination) { (complete) in
                    if complete{
                        completion(true)
                    }else{
                        completion(false)
                    }
                }
            }catch{
                print("current file could not be deleted")
            }
        }
    // download the data from your url
    }else{
        self.saveFile(url: url, destination: destination) { (complete) in
            if complete{
                completion(true)
            }else{
                completion(false)
            }
        }
    }
}


func saveFile(url: URL, destination: URL, completion: @escaping (Bool) -> Void){
    URLSession.shared.downloadTask(with: url, completionHandler: { (location, response, error) in
        // after downloading your data you need to save it to your destination url
        guard
            let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
            let location = location, error == nil
            else { print("error with the url response"); completion(false); return}
        do {
            try FileManager.default.moveItem(at: location, to: destination)
            print("new file saved")
            completion(true)
        } catch {
            print("file could not be saved: \(error)")
            completion(false)
        }
    }).resume()
}