swift3 - 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") 来编写字典时，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 - 命名有点困惑 ;-) ).

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:你可以让 store 方法 can throw 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))
}