Download file from server using Swift

问题

Hi I have a whole bunch of .mp3 files I want to use with NSFileManager and store in the documents folder. Is there a way I can download the .mp3 files online and then have it save to the documents folder? This is what I'm using for a local file.

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")
}

回答1:

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().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()
    }
}

回答2:

Xcode 10.1, Swift 4

I used the example above from @leo-dabus but broke up the code a bit into two functions. One flaw I found in that approach was that it did not handle the case where the file is already downloaded.

This example will remove any previous file that was already downloaded and write the latest version.

/// 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()
}

来源：https://stackoverflow.com/questions/27540068/download-file-from-server-using-swift