如何将字典写入文件？

Question

我有一个 FileHelper 类，我在其中实现了 3 个方法，它们的工作是将字典内容写入文件。这些方法是：

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
}

当我调用FileHelper().storeDictionary(aValidDictionary, inFile: "abc", atDirectory: "XYZ") 编写字典时，此过程失败。但是如果我使用

guard (dictionary as NSDictionary).write(to: filePath!, atomically: true) else {
    return false
}

它有效。

NSKeyedArchiver.archiveRootObject(_:toFile:) 方法有什么问题？？

为什么FileManager.default.createFile(atPath: (filePath?.absoluteString)!, contents: nil, attributes: nil)总是返回false？

Answer 1

首先filePath?.absoluteString 返回包括file:// 方案在内的整个字符串（甚至转义百分比），并且该方法需要一个没有该方案的路径（filePath?.path - 命名有点混乱;-)）。

我建议将[String:String] 字典保存为属性列表文件。无需显式创建文件。

我在 Swift-3-way 中稍微更改了方法的签名。此外，无需使用任何可选类型。

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：您可以让 store 方法可以抛出并在调用方法中处理错误，而不是返回 Bool：

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

这是一个 swift 5 扩展，它应该保存 Key 和 Value 为 Codable 的任何字典

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
    }
}

用法：

let myDict = [MyKey: MyValue].load(from: diskDirectory, andFileName: diskFileName) // load
try myDict.saveToDisk(on: diskDirectory, withName: diskFileName) // save