How to write Dictionary to a file? - swift3

Question

I have a FileHelper class where I've implemented 3 methods whose job is to write a Dictionary contents to a file. Those methods are:
func storeDictionary(_ dictionary: Dictionary<String, String>, inFile fileName: String, atDirectory directory: String) -> Bool {
let ext = "txt"
let filePath = createFile(fileName, withExtension: ext, atDirectory: directory)
/**** //If I use this method, file is created and dictionary is saved
guard (dictionary as NSDictionary).write(to: filePath!, atomically: true) else {
return false
}
*/
guard NSKeyedArchiver.archiveRootObject(dictionary, toFile: (filePath?.absoluteString)!) else {
return false
}
return true
}
func createFile(_ file: String, withExtension ext: String, atDirectory directory: String) -> URL? {
let directoryPath = createDirectory(directory)
let filePath = directoryPath?.appendingPathComponent(file).appendingPathExtension(ext)
if !FileManager.default.fileExists(atPath: (filePath?.absoluteString)!) {
let success = FileManager.default.createFile(atPath: (filePath?.absoluteString)!, contents: nil, attributes: nil)
print("\(success)") //** here is the issue I investigated. Always prints false.
}
return filePath
}
func createDirectory(_ directory: String) -> URL? {
let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
let directoryPath = documentsDirectory.appendingPathComponent(directory)
do {
try FileManager.default.createDirectory(at: directoryPath, withIntermediateDirectories: true, attributes: nil)
} catch let error as NSError {
fatalError("Error creating directory: \(error.localizedDescription)")
}
return directoryPath
}
When I call FileHelper().storeDictionary(aValidDictionary, inFile: "abc", atDirectory: "XYZ") to write the dictionary, it fails with this procedure. But if I use
guard (dictionary as NSDictionary).write(to: filePath!, atomically: true) else {
return false
}
it works.
What's wrong with NSKeyedArchiver.archiveRootObject(_:toFile:) method??
And why FileManager.default.createFile(atPath: (filePath?.absoluteString)!, contents: nil, attributes: nil) always returns false?

Answer 1

First of all filePath?.absoluteString returns the entire – even percent escaped – string including the file:// scheme and the method expects a path without the scheme (filePath?.path - the naming is a bit confusing ;-) ).
I recommend to save a [String:String] dictionary as property list file. It's not necessary to create the file explicitly.
I changed the signatures of the methods slightly in the Swift-3-way. Further there is no need to use any optional type.
func store(dictionary: Dictionary<String, String>, in fileName: String, at directory: String) -> Bool {
let fileExtension = "plist"
let directoryURL = create(directory:directory)
do {
let data = try PropertyListSerialization.data(fromPropertyList: dictionary, format: .xml, options: 0)
try data.write(to: directoryURL.appendingPathComponent(fileName).appendingPathExtension(fileExtension))
return true
} catch {
print(error)
return false
}
}
func create(directory: String) -> URL {
let documentsDirectory = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0]
let directoryURL = documentsDirectory.appendingPathComponent(directory)
do {
try FileManager.default.createDirectory(at: directoryURL, withIntermediateDirectories: true, attributes: nil)
} catch let error as NSError {
fatalError("Error creating directory: \(error.localizedDescription)")
}
return directoryURL
}
PS: Instead of returning a Bool you could make the store method can throw and handle the error in the calling method:
func store(dictionary: Dictionary<String, String>, in fileName: String, at directory: String) throws {
let fileExtension = "plist"
let directoryURL = create(directory:directory)
let data = try PropertyListSerialization.data(fromPropertyList: dictionary, format: .xml, options: 0)
try data.write(to: directoryURL.appendingPathComponent(fileName).appendingPathExtension(fileExtension))
}

Answer 2

Here's a swift 5 extension that should save any Dictionary where the Key and Value are Codable
extension Dictionary where Key: Codable, Value: Codable {
static func load(fromFileName fileName: String, using fileManager: FileManager = .default) -> [Key: Value]? {
let fileURL = Self.getDocumentsURL(on: .cachesDirectory, withName: fileName, using: fileManager)
guard let data = fileManager.contents(atPath: fileURL.path) else { return nil }
do {
return try JSONDecoder().decode([Key: Value].self, from: data)
} catch(let error) {
print(error)
return nil
}
}
func saveToDisk(on directory: FileManager.SearchPathDirectory,
withName name: String,
using fileManager: FileManager = .default) throws {
let fileURL = Self.getDocumentsURL(on: .cachesDirectory, withName: name, using: fileManager)
let data = try JSONEncoder().encode(self)
try data.write(to: fileURL)
}
private static func getDocumentsURL(on directory: FileManager.SearchPathDirectory,
withName name: String,
using fileManager: FileManager) -> URL {
let folderURLs = fileManager.urls(for: .cachesDirectory, in: .userDomainMask)
let fileURL = folderURLs[0].appendingPathComponent(name)
return fileURL
}
}
Usage:
let myDict = [MyKey: MyValue].load(from: diskDirectory, andFileName: diskFileName) // load
try myDict.saveToDisk(on: diskDirectory, withName: diskFileName) // save