如何在Swift中将数组保存为json文件？

Question

我是新手,我很难解决这个问题.所以我需要做的是将此数组保存为iphone文档文件夹中的json文件.

var levels = ["unlocked", "locked", "locked"]

然后才能将它读回另一个数组.有人可以告诉我该怎么做？或提供完成此操作的确切代码.

编辑:我找到了一个例子.这是他们设置数据的方式:

 "[ {"person": {"name":"Dani","age":"24"}}, {"person": {"name":"ray","age":"70"}} ]" 

你可以这样访问它:

 if let item = json[0] 
   { if let person = item["person"] 
     { if let age = person["age"] 
      { println(age) } } }

但我需要能够从保存在文档文件夹中的文件中执行相同的操作.

Answer 1

如果你像我一样不喜欢使用全新的第三方框架只是为了这样一件小事,那么这就是我在vanilla Swift中的解决方案.从在Documents文件夹中创建.json文件到将JSON写入其中.

let documentsDirectoryPathString = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true).first!
let documentsDirectoryPath = NSURL(string: documentsDirectoryPathString)!

let jsonFilePath = documentsDirectoryPath.URLByAppendingPathComponent("test.json")
let fileManager = NSFileManager.defaultManager()
var isDirectory: ObjCBool = false

// creating a .json file in the Documents folder
if !fileManager.fileExistsAtPath(jsonFilePath.absoluteString, isDirectory: &isDirectory) {
    let created = fileManager.createFileAtPath(jsonFilePath.absoluteString, contents: nil, attributes: nil)
    if created {
        print("File created ")
    } else {
        print("Couldn't create file for some reason")
    }
} else {
    print("File already exists")
}

// creating an array of test data
var numbers = [String]()
for var i = 0; i < 100; i++ {
    numbers.append("Test\(i)")
}

// creating JSON out of the above array
var jsonData: NSData!
do {
    jsonData = try NSJSONSerialization.dataWithJSONObject(numbers, options: NSJSONWritingOptions())
    let jsonString = String(data: jsonData, encoding: NSUTF8StringEncoding)
    print(jsonString)
} catch let error as NSError {
    print("Array to JSON conversion failed: \(error.localizedDescription)")
}

// Write that JSON to the file created earlier
let jsonFilePath = documentsDirectoryPath.URLByAppendingPathComponent("test.json")
do {
    let file = try NSFileHandle(forWritingToURL: jsonFilePath)
    file.writeData(jsonData)
    print("JSON data was written to teh file successfully!")
} catch let error as NSError {
    print("Couldn't write to file: \(error.localizedDescription)")
}

Answer 2

#1.将Swift保存Array为json文件

下面的斯威夫特3/iOS的10码演示了如何变换一个Array实例为JSON数据并将其保存到位于使用iPhone的文档目录中的一个JSON文件FileManager和JSONSerialization:

func saveToJsonFile() {
    // Get the url of Persons.json in document directory
    guard let documentDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
    let fileUrl = documentDirectoryUrl.appendingPathComponent("Persons.json")

    let personArray =  [["person": ["name": "Dani", "age": "24"]], ["person": ["name": "ray", "age": "70"]]]

    // Transform array into data and save it into file
    do {
        let data = try JSONSerialization.data(withJSONObject: personArray, options: [])
        try data.write(to: fileUrl, options: [])
    } catch {
        print(error)
    }
}

/*
 Content of Persons.json file after operation:
 [{"person":{"name":"Dani","age":"24"}},{"person":{"name":"ray","age":"70"}}]
*/

作为替代方案,您可以实现以下使用流的代码:

func saveToJsonFile() {
    // Get the url of Persons.json in document directory
    guard let documentDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
    let fileUrl = documentDirectoryUrl.appendingPathComponent("Persons.json")

    let personArray =  [["person": ["name": "Dani", "age": "24"]], ["person": ["name": "ray", "age": "70"]]]

    // Create a write-only stream
    guard let stream = OutputStream(toFileAtPath: fileUrl.path, append: false) else { return }
    stream.open()
    defer {
        stream.close()
    }

    // Transform array into data and save it into file
    var error: NSError?
    JSONSerialization.writeJSONObject(personArray, to: stream, options: [], error: &error)

    // Handle error
    if let error = error {
        print(error)
    }
}

/*
 Content of Persons.json file after operation:
 [{"person":{"name":"Dani","age":"24"}},{"person":{"name":"ray","age":"70"}}]
*/

#2.Array从json文件中获取Swift

以下Swift 3/iOS 10代码显示了如何从位于iPhone文档目录中的json文件获取数据,并Array使用FileManager和将其转换为实例JSONSerialization:

/*
 Content of Persons.json file:
 [{"person":{"name":"Dani","age":"24"}},{"person":{"name":"ray","age":"70"}}]
*/

func retrieveFromJsonFile() {
    // Get the url of Persons.json in document directory
    guard let documentsDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
    let fileUrl = documentsDirectoryUrl.appendingPathComponent("Persons.json")

    // Read data from .json file and transform data into an array
    do {
        let data = try Data(contentsOf: fileUrl, options: [])
        guard let personArray = try JSONSerialization.jsonObject(with: data, options: []) as? [[String: [String: String]]] else { return }
        print(personArray) // prints [["person": ["name": "Dani", "age": "24"]], ["person": ["name": "ray", "age": "70"]]]
    } catch {
        print(error)
    }
}

作为替代方案,您可以实现以下使用流的代码:

/*
 Content of Persons.json file:
 [{"person":{"name":"Dani","age":"24"}},{"person":{"name":"ray","age":"70"}}]
*/

func retrieveFromJsonFile() {
    // Get the url of Persons.json in document directory
    guard let documentsDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
    let fileUrl = documentsDirectoryUrl.appendingPathComponent("Persons.json")

    // Create a read-only stream
    guard let stream = InputStream(url: fileUrl) else { return }
    stream.open()
    defer {
        stream.close()
    }

    // Read data from .json file and transform data into an array
    do {
        guard let personArray = try JSONSerialization.jsonObject(with: stream, options: []) as? [[String: [String: String]]] else { return }
        print(personArray) // prints [["person": ["name": "Dani", "age": "24"]], ["person": ["name": "ray", "age": "70"]]]
    } catch {
        print(error)
    }
}

位于Github的Save-and-read-JSON-from-Playground repo中的Playground显示了如何将Swift保存Array到json文件以及如何读取json文件并从中获取Swift Array.

Answer 3

我建议你使用SwiftyJSON框架.究其文档和除学习如何将字符串写入到文件(提示:NSFileHandle)

类似下面的代码,但你真的需要学习SwiftyJSON和NSFileHandle来学习如何将JSON数据序列化到文件并解析文件中的JSON数据

let levels = ["unlocked", "locked", "locked"]
let json = JSON(levels)
let str = json.description
let data = str.dataUsingEncoding(NSUTF8StringEncoding)!
if let file = NSFileHandle(forWritingAtPath:path) {
    file.writeData(data)
} 

Answer 4

在Swift 4中，它已经内置了JSONEncoder。

let pathDirectory = getDocumentsDirectory()
try? FileManager().createDirectory(at: pathDirectory, withIntermediateDirectories: true)
let filePath = pathDirectory.appendingPathComponent("levels.json")

let levels = ["unlocked", "locked", "locked"]
let json = try? JSONEncoder().encode(levels)

do {
     try json!.write(to: filePath)
} catch {
    print("Failed to write JSON data: \(error.localizedDescription)")
}

func getDocumentsDirectory() -> URL {
    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    return paths[0]
}

您要编码的对象必须符合Encodable协议。

阅读有关如何扩展现有对象以使其可编码的苹果官方指南。