如何保存一个。如果使用filemanager连接,则在USB上使用Swift 3的txt文件?(macOS应用程序开发)

这可能是基于上述问题: Read and write data from text file

我想做的是,如果连接了某种类型的可移动卷,可以选择直接在驱动器上写入文件,如果可能的话,可以在该驱动器的某个子文件夹中写入文件。

let fileManager = FileManager.default
var Extension: String = "txt"
let FileName: String = "TestFileName"
var DocumentDirURL = try! FileManager.default.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: true)
let fileURL = DocumentDirURL.appendingPathComponent(FileName).appendingPathExtension(Extension)
print("FilePath: \(fileURL.path)")
let DocumentIntro = "This text will be on the text file\n"
do {
    // Write to the file
    try DocumentIntro.write(to: fileURL, atomically: true, encoding: String.Encoding.utf8)
} catch let error as NSError {
    print("Failed writing to URL: \(fileURL), Error: " + error.localizedDescription)
}
var FileContents = "" // Used to store the file contents
do {
    // Read the file contents
    FileContents = try String(contentsOf: fileURL)
} catch let error as NSError 
    print("Failed reading from URL: \(fileURL), Error: " + error.localizedDescription)
}