斯威夫特编码如何使用任何类型?

Question

当我尝试访问"value"的值时，例如在label.text中使用它时，我收到一个错误

无法将类型"MyValue？"的值分配给类型"字符串？">

？

当我将值打印到终端时，它说...

0x109d06188(的未知上下文(。MyValue.string...

如何解决这个问题？

struct Root: Codable {
let description,id: String
let group,groupDescription: String?
let name: String
let value: MyValue
enum CodingKeys: String, CodingKey {
case description = "Description"
case group = "Group"
case groupDescription = "GroupDescription"
case id = "Id"
case name = "Name"
case value = "Value"
}
}
enum MyValue: Codable {
case string(String)
case innerItem(InnerItem)
init(from decoder: Decoder) throws {
let container = try decoder.singleValueContainer()
if let x = try? container.decode(String.self) {
self = .string(x)
return
}
if let x = try? container.decode(InnerItem.self) {
self = .innerItem(x)
return
}
throw DecodingError.typeMismatch(MyValue.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for MyValue"))
}
func encode(to encoder: Encoder) throws {
var container = encoder.singleValueContainer()
switch self {
case .string(let x):
try container.encode(x)
case .innerItem(let x):
try container.encode(x)
}
}
}

Answer 1

您可以通过符合 rawRepresentable 协议来获取标签的字符串值：

enum MyValue: Codable, RawRepresentable {

var rawValue: String {
switch self {
case .string(let stringVal):
return stringVal
case .innerItem(let myVal):
return String(describing: myVal)
}
}
typealias RawValue = String
init?(rawValue: String) {
return nil
}

case string(String)
case innerItem(InnerItem)
}
let myVal = MyValue.string("testString")
var strVal: String = myVal.rawValue // testString

Answer 2

要在枚举中获取关联的值，您可以在MyValue中添加两个计算属性

var stringValue : String? {
guard case .string(let string) = self else { return nil }
return string
}
var innerItemValue : InnerItem? {
guard case .innerItem(let innerItem) = self else { return nil }
return innerItem
}

或者像encode方法一样打开value

switch root.value {
case .string(let string): // do something with `string`
case .innerItem(let innerItem):  // do something with `innerItem`
}

或者干脆使用if case

if case .string(let string) = root.value { someLabel.text = string }