将文件从音乐库导出到Documents目录(Swift 5)

Question

在我的应用程序中，我想从音乐库导出文件并将其保存到Documents目录。我已经从音乐库中获取了文件列表，并获得了每个文件的url。但我仍然有两个问题：

1. 我只能在"；m4a"；格式，但我想以音乐库中的文件格式导出(mp3、wav、aac或其他(

2. 如何使用url将音乐库中的文件保存到Documents目录？我的代码现在看起来是这样的：

   private func exportFile(with assetURL: URL, completionHandler: @escaping (_ fileURL: URL?, _ error: Error?) -> ()) {
   let asset = AVURLAsset(url: assetURL)
   guard let exporter = AVAssetExportSession(asset: asset, presetName: AVAssetExportPresetAppleM4A) else {
   completionHandler(nil, nil)
   return
   }
   let fileURL = URL(fileURLWithPath: NSTemporaryDirectory())
   .appendingPathComponent(NSUUID().uuidString)
   .appendingPathExtension("m4a")
   exporter.outputURL = fileURL
   exporter.outputFileType = AVFileType.m4a
   exporter.exportAsynchronously {
   if exporter.status == .completed {
   completionHandler(fileURL, nil)
   } else {
   completionHandler(nil, exporter.error)
   }
   }
   func downloadFile(file: MPMediaItem?, callback: @escaping () -> ()) {
   guard let file = file,
   let url = file.url
   else { return }
   exportFile(with: url) { fileURL, error in
   guard let fileURL = fileURL, error == nil else {
   print(error?.localizedDescription)
   return
   }
   //Here I'd like to save file to Documents dir
   print("(fileURL)")
   }
   callback()
   }
   

Answer 1

第二个问题的解决方案

我把代码放在一种方法中，并直接保存到Documents文件夹，而不是临时文件夹：

func downloadFile(file: MPMediaItem?, callback: @escaping () -> ()) {
guard let file = file,
let url = file.assetURL
else { return }
let exportSession = AVAssetExportSession(asset: AVAsset(url: url), presetName: AVAssetExportPresetAppleM4A)
exportSession?.shouldOptimizeForNetworkUse = true
exportSession?.outputFileType = AVFileType.m4a

let documentURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
let outputURL = documentURL.appendingPathComponent("(file.title!).m4a")
//        //Delete Existing file if needs
//        do {
//              try FileManager.default.removeItem(at: outputURL)
//        } catch let error as NSError {
//              print(error.debugDescription)
//        }
exportSession?.outputURL = outputURL
exportSession?.exportAsynchronously(completionHandler: { () -> () in

if exportSession!.status == AVAssetExportSession.Status.completed  {
print("Export Successful")
DispatchQueue.main.async {
//Update IU
callback()
}
} else {
print("Export failed")
}
})
}