在Swift 3中使用选项的JSONSerialization

Question

在Swift 3中,JSONSerialization具有可选值的数组失败.
这在Swift 2中起作用(产生null作为nil期望的可选项的JSON值).

编辑:它没有,但留在这里,因为这是我提出问题时的错误信念.

斯威夫特2:

let a: [String!] = ["a","b","c"]
let b: [String] = ["a","b","c"]

let s: String! = "a"
let c = ["a",s]

NSJSONSerialization.isValidJSONObject(a)    //true
NSJSONSerialization.isValidJSONObject(b)    //true
NSJSONSerialization.isValidJSONObject(c)    //true

斯威夫特3:

let a: [String?] = ["a","b","c"]
let b: [String] = ["a","b","c"]

let s: String! = "a"
let c = ["a",s]

JSONSerialization.isValidJSONObject(a)    //false
JSONSerialization.isValidJSONObject(b)    //true
JSONSerialization.isValidJSONObject(c)    //false

这是预期的变化吗？
它似乎非常容易出错,因为任何使用隐式类型构造的数组或字典现在可能对JSON无效(即使它们实际上不包含任何nil值).

另外,如何指定空值？

Answer 1

更新:从Swift 3.0.1/Xcode 8.1 beta 2开始,选项会NSNull自动桥接到实例,请参阅

• SE-0140 - 可选时转换为任意警告,并将可选作为其有效负载或NSNull桥接

和Xcode 8.1测试版发行说明.

例:

let array: [String?] = [ "a", nil, "c"]
let jsonData = try! JSONSerialization.data(withJSONObject: array)

print(String(data: jsonData, encoding: .utf8)!)
// ["a",null,"c"]

Swift 2和3.0的上一个答案:仅NSNull()序列化为JSON null,而不是选项(独立于Swift版本).

可以像这样转换一组选项:

let a: [String?] = ["a", nil, "c"]

let b = a.map { $0 as Any? ?? NSNull() }
print(b) // ["a", <null>, "c"]

let d = try! JSONSerialization.data(withJSONObject: b)
print(String(data: d, encoding: .utf8)!) // ["a",null,"c"]