问题
I'm currently working with Codable types in my project and facing an issue.
struct Person: Codable
{
var id: Any
}
id in the above code could be either a String or an Int. This is the reason id is of type Any.
I know that Any is not Codable.
What I need to know is how can I make it work.
回答1:
Codable needs to know the type to cast to.
Firstly I would try to address the issue of not knowing the type, see if you can fix that and make it simpler.
Otherwise the only way I can think of solving your issue currently is to use generics like below.
struct Person<T> {
var id: T
var name: String
}
let person1 = Person<Int>(id: 1, name: "John")
let person2 = Person<String>(id: "two", name: "Steve")
回答2:
Quantum Value
First of all you can define a type that can be decoded both from a String and Int value.
Here it is.
enum QuantumValue: Decodable {
case int(Int), string(String)
init(from decoder: Decoder) throws {
if let int = try? decoder.singleValueContainer().decode(Int.self) {
self = .int(int)
return
}
if let string = try? decoder.singleValueContainer().decode(String.self) {
self = .string(string)
return
}
throw QuantumError.missingValue
}
enum QuantumError:Error {
case missingValue
}
}
Person
Now you can define your struct like this
struct Person: Decodable {
let id: QuantumValue
}
That's it. Let's test it!
JSON 1: id is String
let data = """
{
"id": "123"
}
""".data(using: String.Encoding.utf8)!
if let person = try? JSONDecoder().decode(Person.self, from: data) {
print(person)
}
JSON 2: id is Int
let data = """
{
"id": 123
}
""".data(using: String.Encoding.utf8)!
if let person = try? JSONDecoder().decode(Person.self, from: data) {
print(person)
}
[UPDATE] Comparing values
This new paragraph should answer the questions from the comments.
If you want to compare a quantum value to an Int you must keep in mind that a quantum value could contain an Int or a String.
So the question is: what does it mean comparing a String and an Int?
If you are just looking for a way of converting a quantum value into an Int then you can simply add this extension
extension QuantumValue {
var intValue: Int? {
switch self {
case .int(let value): return value
case .string(let value): return Int(value)
}
}
}
Now you can write
let quantumValue: QuantumValue: ...
quantumValue.intValue == 123
回答3:
I solved this issue defining a new Decodable Struct called AnyDecodable, so instead of Any I use AnyDecodable. It works perfectly also with nested types.
Try this in a playground:
var json = """
{
"id": 12345,
"name": "Giuseppe",
"last_name": "Lanza",
"age": 31,
"happy": true,
"rate": 1.5,
"classes": ["maths", "phisics"],
"dogs": [
{
"name": "Gala",
"age": 1
}, {
"name": "Aria",
"age": 3
}
]
}
"""
public struct AnyDecodable: Decodable {
public var value: Any
private struct CodingKeys: CodingKey {
var stringValue: String
var intValue: Int?
init?(intValue: Int) {
self.stringValue = "\(intValue)"
self.intValue = intValue
}
init?(stringValue: String) { self.stringValue = stringValue }
}
public init(from decoder: Decoder) throws {
if let container = try? decoder.container(keyedBy: CodingKeys.self) {
var result = [String: Any]()
try container.allKeys.forEach { (key) throws in
result[key.stringValue] = try container.decode(AnyDecodable.self, forKey: key).value
}
value = result
} else if var container = try? decoder.unkeyedContainer() {
var result = [Any]()
while !container.isAtEnd {
result.append(try container.decode(AnyDecodable.self).value)
}
value = result
} else if let container = try? decoder.singleValueContainer() {
if let intVal = try? container.decode(Int.self) {
value = intVal
} else if let doubleVal = try? container.decode(Double.self) {
value = doubleVal
} else if let boolVal = try? container.decode(Bool.self) {
value = boolVal
} else if let stringVal = try? container.decode(String.self) {
value = stringVal
} else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "the container contains nothing serialisable")
}
} else {
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Could not serialise"))
}
}
}
let stud = try! JSONDecoder().decode(AnyDecodable.self, from: jsonData).value as! [String: Any]
print(stud)
You could extend my struct to be AnyCodable if you are interested also in the Encoding part.
Edit: I actually did it.
Here is AnyCodable
struct AnyCodable: Decodable {
var value: Any
struct CodingKeys: CodingKey {
var stringValue: String
var intValue: Int?
init?(intValue: Int) {
self.stringValue = "\(intValue)"
self.intValue = intValue
}
init?(stringValue: String) { self.stringValue = stringValue }
}
init(value: Any) {
self.value = value
}
init(from decoder: Decoder) throws {
if let container = try? decoder.container(keyedBy: CodingKeys.self) {
var result = [String: Any]()
try container.allKeys.forEach { (key) throws in
result[key.stringValue] = try container.decode(AnyCodable.self, forKey: key).value
}
value = result
} else if var container = try? decoder.unkeyedContainer() {
var result = [Any]()
while !container.isAtEnd {
result.append(try container.decode(AnyCodable.self).value)
}
value = result
} else if let container = try? decoder.singleValueContainer() {
if let intVal = try? container.decode(Int.self) {
value = intVal
} else if let doubleVal = try? container.decode(Double.self) {
value = doubleVal
} else if let boolVal = try? container.decode(Bool.self) {
value = boolVal
} else if let stringVal = try? container.decode(String.self) {
value = stringVal
} else {
throw DecodingError.dataCorruptedError(in: container, debugDescription: "the container contains nothing serialisable")
}
} else {
throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Could not serialise"))
}
}
}
extension AnyCodable: Encodable {
func encode(to encoder: Encoder) throws {
if let array = value as? [Any] {
var container = encoder.unkeyedContainer()
for value in array {
let decodable = AnyCodable(value: value)
try container.encode(decodable)
}
} else if let dictionary = value as? [String: Any] {
var container = encoder.container(keyedBy: CodingKeys.self)
for (key, value) in dictionary {
let codingKey = CodingKeys(stringValue: key)!
let decodable = AnyCodable(value: value)
try container.encode(decodable, forKey: codingKey)
}
} else {
var container = encoder.singleValueContainer()
if let intVal = value as? Int {
try container.encode(intVal)
} else if let doubleVal = value as? Double {
try container.encode(doubleVal)
} else if let boolVal = value as? Bool {
try container.encode(boolVal)
} else if let stringVal = value as? String {
try container.encode(stringVal)
} else {
throw EncodingError.invalidValue(value, EncodingError.Context.init(codingPath: [], debugDescription: "The value is not encodable"))
}
}
}
}
You can test it With the previous json in this way in a playground:
let stud = try! JSONDecoder().decode(AnyCodable.self, from: jsonData)
print(stud.value as! [String: Any])
let backToJson = try! JSONEncoder().encode(stud)
let jsonString = String(bytes: backToJson, encoding: .utf8)!
print(jsonString)
回答4:
If your problem is that it's uncertain the type of id as it might be either a string or an integer value, I can suggest you this blog post: http://agostini.tech/2017/11/12/swift-4-codable-in-real-life-part-2/
Basically I defined a new Decodable type
public struct UncertainValue<T: Decodable, U: Decodable>: Decodable {
public var tValue: T?
public var uValue: U?
public var value: Any? {
return tValue ?? uValue
}
public init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
tValue = try? container.decode(T.self)
uValue = try? container.decode(U.self)
if tValue == nil && uValue == nil {
//Type mismatch
throw DecodingError.typeMismatch(type(of: self), DecodingError.Context(codingPath: [], debugDescription: "The value is not of type \(T.self) and not even \(U.self)"))
}
}
}
From now on, your Person object would be
struct Person: Decodable {
var id: UncertainValue<Int, String>
}
you will be able to access your id using id.value
回答5:
You can replace Any with an enum accepting an Int or a String:
enum Id: Codable {
case numeric(value: Int)
case named(name: String)
}
struct Person: Codable
{
var id: Id
}
Then the compiler will complain about the fact that Id does not conform to Decodable. Because Id has associated values you need to implement this yourself. Read https://littlebitesofcocoa.com/318-codable-enums for an example of how to do this.
回答6:
To make key as Any, I like all above answers. But when you are not sure which data type your server guy will send then you use Quantum class (as above), But Quantum type is little difficult to use or manage. So here is my solution to make your decodable class key as a Any data type (or "id" for obj-c lovers)
class StatusResp:Decodable{
var success:Id? // Here i am not sure which datatype my server guy will send
}
enum Id: Decodable {
case int(Int), double(Double), string(String) // Add more cases if you want
init(from decoder: Decoder) throws {
//Check each case
if let dbl = try? decoder.singleValueContainer().decode(Double.self),dbl.truncatingRemainder(dividingBy: 1) != 0 { // It is double not a int value
self = .double(dbl)
return
}
if let int = try? decoder.singleValueContainer().decode(Int.self) {
self = .int(int)
return
}
if let string = try? decoder.singleValueContainer().decode(String.self) {
self = .string(string)
return
}
throw IdError.missingValue
}
enum IdError:Error { // If no case matched
case missingValue
}
var any:Any{
get{
switch self {
case .double(let value):
return value
case .int(let value):
return value
case .string(let value):
return value
}
}
}
}
Usage :
let json = "{\"success\":\"hii\"}".data(using: .utf8) // response will be String
//let json = "{\"success\":50.55}".data(using: .utf8) //response will be Double
//let json = "{\"success\":50}".data(using: .utf8) //response will be Int
let decoded = try? JSONDecoder().decode(StatusResp.self, from: json!)
print(decoded?.success) // It will print Any
if let doubleValue = decoded?.success as? Double {
}else if let doubleValue = decoded?.success as? Int {
}else if let doubleValue = decoded?.success as? String {
}
回答7:
Here your id can be any Codable type:
Swift 4.2
struct Person<T: Codable>: Codable {
var id: T
var name: String?
}
let p1 = Person(id: 1, name: "Bill")
let p2 = Person(id: "one", name: "John")
回答8:
First of all, as you can read in other answers and comments, using Any for this is not good design. If possible, give it a second thought.
That said, if you want to stick to it for your own reasons, you should write your own encoding/decoding and adopt some kind of convention in the serialized JSON.
The code below implements it by encoding id always as string and decoding to Int or String depending on the found value.
import Foundation
struct Person: Codable {
var id: Any
init(id: Any) {
self.id = id
}
public init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: Keys.self)
if let idstr = try container.decodeIfPresent(String.self, forKey: .id) {
if let idnum = Int(idstr) {
id = idnum
}
else {
id = idstr
}
return
}
fatalError()
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: Keys.self)
try container.encode(String(describing: id), forKey: .id)
}
enum Keys: String, CodingKey {
case id
}
}
extension Person: CustomStringConvertible {
var description: String { return "<Person id:\(id)>" }
}
Examples
Encode object with numeric id:
var p1 = Person(id: 1)
print(String(data: try JSONEncoder().encode(p1),
encoding: String.Encoding.utf8) ?? "/* ERROR */")
// {"id":"1"}
Encode object with string id:
var p2 = Person(id: "root")
print(String(data: try JSONEncoder().encode(p2),
encoding: String.Encoding.utf8) ?? "/* ERROR */")
// {"id":"root"}
Decode to numeric id:
print(try JSONDecoder().decode(Person.self,
from: "{\"id\": \"2\"}".data(using: String.Encoding.utf8)!))
// <Person id:2>
Decode to string id:
print(try JSONDecoder().decode(Person.self,
from: "{\"id\": \"admin\"}".data(using: String.Encoding.utf8)!))
// <Person id:admin>
An alternative implementation would be encoding to Int or String and wrap the decoding attempts in a do...catch.
In the encoding part:
if let idstr = id as? String {
try container.encode(idstr, forKey: .id)
}
else if let idnum = id as? Int {
try container.encode(idnum, forKey: .id)
}
And then decode to the right type in multiple attempts:
do {
if let idstr = try container.decodeIfPresent(String.self, forKey: .id) {
id = idstr
id_decoded = true
}
}
catch {
/* pass */
}
if !id_decoded {
do {
if let idnum = try container.decodeIfPresent(Int.self, forKey: .id) {
id = idnum
}
}
catch {
/* pass */
}
}
It's uglier in my opinion.
Depending on the control you have over the server serialization you can use either of them or write something else adapted to the actual serialization.
回答9:
Simply you can use AnyCodable type from Matt Thompson's cool library AnyCodable.
Eg:
import AnyCodable
struct Person: Codable
{
var id: AnyCodable
}
回答10:
There is a corner case which is not covered by Luca Angeletti's solution.
For instance, if Cordinate's type is Double or [Double], Angeletti's solution will cause an error: "Expected to decode Double but found an array instead"
In this case, you have to use nested enum instead in Cordinate.
enum Cordinate: Decodable {
case double(Double), array([Cordinate])
init(from decoder: Decoder) throws {
if let double = try? decoder.singleValueContainer().decode(Double.self) {
self = .double(double)
return
}
if let array = try? decoder.singleValueContainer().decode([Cordinate].self) {
self = .array(array)
return
}
throw CordinateError.missingValue
}
enum CordinateError: Error {
case missingValue
}
}
struct Geometry : Decodable {
let date : String?
let type : String?
let coordinates : [Cordinate]?
enum CodingKeys: String, CodingKey {
case date = "date"
case type = "type"
case coordinates = "coordinates"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
date = try values.decodeIfPresent(String.self, forKey: .date)
type = try values.decodeIfPresent(String.self, forKey: .type)
coordinates = try values.decodeIfPresent([Cordinate].self, forKey: .coordinates)
}
}
来源：https://stackoverflow.com/questions/48297263/how-to-use-any-in-codable-type