[英]How to decode a dictionary into struct with key as a value in Swift
I need to decode a dictionary like:我需要解码一个字典,如:
{
"Bob": "London",
"Alice": "Berlin"
...
}
Into an array of Person
structs:进入Person
结构数组:
struct Person {
let name: String
let city: String
}
I would like to implement this mapping using Coding
protocol, but struggling to use each key as a value for the struct.我想使用Coding
协议来实现这个映射,但很难将每个键用作结构的值。
Q: What about
NSJsonSerialization
?问:NSJsonSerialization
怎么样?A: I know it's quite trivial with
NSJsonSerialization
, but implementing it withDecodable
protocol was bugging me a bit :)答:我知道NSJsonSerialization
很简单,但是用Decodable
协议实现它让我有点Decodable
:)
Some more thought reminded me I don't need AnyCodingKey in this case because this is such a simple structure.更多的想法提醒我在这种情况下我不需要 AnyCodingKey 因为这是一个如此简单的结构。 Decode as a [String: String]
, and then make the mapping:解码为[String: String]
,然后进行映射:
struct PersonList: Decodable {
let persons: [Person]
init(from decoder: Decoder) throws {
self.persons = try decoder.singleValueContainer()
.decode([String: String].self)
.map(Person.init)
}
}
let list = try JSONDecoder().decode(PersonList.self, from: json).persons
// [Person(name: "Bob", city: "London"), Person(name: "Alice", city: "Berlin")]
Old answer, because sometimes this technique is handy.旧答案,因为有时这种技术很方便。
The key tool for this is the oft-needed CodingKey (that really should be in stdlib), AnyCodingKey:对此的关键工具是经常需要的 CodingKey(它确实应该在 stdlib 中),AnyCodingKey:
struct AnyCodingKey: CodingKey {
var stringValue: String = ""
init?(stringValue: String) { self.stringValue = stringValue }
var intValue: Int?
init?(intValue: Int) { self.intValue = intValue }
}
With that, you just need a container to hang the decoder on.有了这个,你只需要一个容器来挂解码器。 Call it PersonList:称之为 PersonList:
struct PersonList: Decodable {
let persons: [Person]
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: AnyCodingKey.self)
self.persons = try container.allKeys.map { key in
Person(name: key.stringValue,
city: try container.decode(String.self, forKey: key))
}
}
}
let list = try JSONDecoder().decode(PersonList.self, from: json).persons
// [Person(name: "Bob", city: "London"), Person(name: "Alice", city: "Berlin")]
This just maps each key/value to a Person.这只是将每个键/值映射到一个人。
Keep in mind that JSON objects are not ordered, so the resulting array may be in a different order than the JSON, as they are in this example.请记住,JSON 对象没有排序,因此结果数组的顺序可能与 JSON 不同,如本示例中所示。 This is not fixable with Foundation (JSONSerialization or JSONDecoder);这无法通过 Foundation(JSONSerialization 或 JSONDecoder)修复; you'd have to use a different JSON parser if you needed that.如果需要,您必须使用不同的 JSON 解析器。
In this case I'd prefer traditional JSONSerialization
, the returned dictionary can be easily mapped to an array of Person
在这种情况下,我希望使用传统的JSONSerialization
,返回的字典可以轻松地映射到Person
数组
let json = """
{
"Bob": "London",
"Alice": "Berlin"
}
"""
struct Person {
let name: String
let city: String
}
do {
if let dataDictionary = try JSONSerialization.jsonObject(with: Data(json.utf8)) as? [String:String] {
let people = dataDictionary.map{Person(name: $0.key, city: $0.value)}
print(people)
}
} catch {
print(error)
}
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