如何将Swift 4编码的JSON写入文件？

Question

如何将通过Swift 4 Codable协议编码的JSON对象写入文件？斯威夫特4以前我用过的JSONSerialization.writeJSONObject,但JSONSerialization.isValidJSONObject现在返回false所创建的数据(或字符串).一个例子:

import Foundation

class Shark : Codable
{
    var name:String = ""
    var carnivorous:Bool = true
    var numOfTeeth:Int = 0
    var hobbies:[String] = []
}

class JSON
{
    class func encode<T:Encodable>(_ obj:T) -> String?
    {
        if let encodedData = try? JSONEncoder().encode(obj)
        {
            return String(data: encodedData, encoding: .utf8)
        }
        return nil
    }

    class func writeToStream(data:Any, path:String) -> Bool
    {
        var success = false
        if JSONSerialization.isValidJSONObject(data)
        {
            if let stream = OutputStream(toFileAtPath: "\(path)", append: false)
            {
                stream.open()
                var error:NSError?
                JSONSerialization.writeJSONObject(data, to: stream, options: [], error: &error)
                stream.close()
                if let error = error
                {
                    print("Failed to write JSON data: \(error.localizedDescription)")
                    success = false
                }
            }
            else
            {
                print("Could not open JSON file stream at \(path).")
                success = false
            }
        }
        else
        {
            print("Data is not a valid format for JSON serialization: \(data)")
            success = false
        }
        return success
    }
}


let shark = Shark()
shark.name = "Nancy"
shark.carnivorous = true
shark.numOfTeeth = 48
shark.hobbies = ["Dancing", "Swiming", "Eating people"]

if let jsonString = JSON.encode(shark)
{
    let success = JSON.writeToStream(data: jsonString.data(using: .utf8), path: "\(NSHomeDirectory())/Documents")
}

这两种格式都无效JSONSerialization.isValidJSONObject():

JSON.writeToStream(data: jsonString, path: "\(NSHomeDirectory())/Documents")
JSON.writeToStream(data: jsonString.data(using: .utf8), path: "\(NSHomeDirectory())/Documents")

数据不是JSON序列化的有效格式:
{"numOfTeeth":48,"爱好":["跳舞","游泳","吃人"],"名称":"南希","食肉":真实}
数据不是JSON序列化的有效格式:可选(99字节)

如何将其传递给JSON验证然后将其写入文件？

Answer 1

JSONSerialization.你的JSONSerialization.isValidJSONObject用法是错误的.正如文件明确指出:

可以转换为JSON的Foundation对象必须具有以下属性:
•顶级对象是NSArray或NSDictionary.
•所有对象的实例NSString,NSNumber,NSArray,NSDictionary,或NSNull.
•所有字典键都是实例NSString.

因此,Data或String类型根本无效;)

编写编码数据.要实际编写生成的内容Data,请使用相应的Data.write(to: URL)方法.例如:

if let encodedData = try? JSONEncoder().encode(obj) {
    let path = "/path/to/obj.json"
    let pathAsURL = URL(fileURLWithPath: path)
    do {
        try encodedData!.write(to: pathAsURL)
    } 
    catch {
        print("Failed to write JSON data: \(error.localizedDescription)")
    }
}

只要标准生成JSON数据,就JSONEncoder不需要进行额外的验证;)