将未知的可枚举枚举值解码为默认值 [英] Decoding unknown Encodable enum values to a default
问题描述
我必须反序列化这样的JSON字符串:
I have to deserialize a JSON string like this:
{ "name" : "John Smith", "value" : "someValue" }
在Swift 4中,其中值"应该是一个枚举,整个对象是一个像这样的结构:
in Swift 4, where "value" should be a enum and the whole object is a struct like:
struct MyType {
name: String?
value: Value?
}
在将来的某个时刻,后端可能会添加新的枚举值,因此我认为进行一些回退是很明智的.
At some point in the future, there might be new enum values added in the backend so I thought it would be smart to have some fallback.
我以为我可以创建像这样的枚举
I thought I could create a enum like
enum Value {
case someValue
case someOtherValue
case unknown(value: String)
}
但是我只是无法解决如何反序列化该枚举并使它正常工作的问题.以前,我只是使用String
枚举,但是反序列化未知值会引发错误.
but I just can't wrap my head around how to deserialize that enum and make it work. Previously I simply used a String
enum, but deserializing unknown values throws errors.
是否有一种简单的方法可以完成该工作,还是应该将值反序列化为String
并使用switch语句在结构中创建自定义getter以返回其中一种情况(可能甚至不在结构本身中,在我看来模型)?
Is there a simple way to make that work or should I deserialize the value as a String
and create a custom getter in the struct with a switch statement to return one of the cases (probably not even in the struct itself but in my view model)?
推荐答案
您可以实现init(from decoder: Decoder)
和encode(to encoder: Encoder)
并显式处理每种情况,即
You can implement init(from decoder: Decoder)
and encode(to encoder: Encoder)
and handle every case explicitly, i.e.
struct MyType: Codable
{
var name: String?
var value: Value?
enum CodingKeys: String, CodingKey
{
case name
case value
}
init(from decoder: Decoder) throws
{
let values = try decoder.container(keyedBy: CodingKeys.self)
name = try values.decode(String.self, forKey: .name)
let strValue = try values.decode(String.self, forKey: .value)
//You need to handle every case explicitly
switch strValue
{
case "someValue":
value = Value.someValue
case "someOtherValue":
value = Value.someOtherValue
default:
value = Value.unknown(value: strValue)
}
}
func encode(to encoder: Encoder) throws
{
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(name, forKey: .name)
if let val = value
{
//You need to handle every case explicitly
switch val
{
case .someValue, .someOtherValue:
try container.encode(String(describing: val), forKey: .value)
case .unknown(let strValue):
try container.encode(strValue, forKey: .value)
}
}
}
}
enum Value
{
case someValue
case someOtherValue
case unknown(value: String)
}
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