可编码继承
Codable with inheritance
我正在使用 Codable 协议序列化和反序列化继承的 classes。我成功地将整个模型序列化为 JSON,但我在反序列化 JSON 时遇到了问题。这是我的数据结构。我的应用程序的某些部分像下面的示例一样工作,此时更改整个数据结构对我们来说工作量太大。
class Base: Codable {
let baseValue: String
init(baseValue :String) {
self.baseValue = baseValue
}
enum SuperCodingKeys: String, CodingKey {
case baseValue
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: SuperCodingKeys.self)
try container.encode(baseValue, forKey: .baseValue)
}
}
class Child1: Base {
let child1Value: Int
init(child1Value: Int, baseValue: String) {
self.child1Value = child1Value
super.init(baseValue: baseValue)
}
private enum CodingKeys: String, CodingKey {
case child1Value
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.child1Value = try container.decode(Int.self, forKey: .child1Value)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(child1Value, forKey: .child1Value)
try super.encode(to: encoder)
}
}
class Child2: Base {
let child2Value: Int
init(child2Value: Int, baseValue: String) {
self.child2Value = child2Value
super.init(baseValue: baseValue)
}
private enum CodingKeys: String, CodingKey {
case child2Value
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.child2Value = try container.decode(Int.self, forKey: .child2Value)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(child2Value, forKey: .child2Value)
try super.encode(to: encoder)
}
}
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
}
这是我为 DataManger 增加价值的方式(顺便说一句,在我的应用程序中,这是一个单例 class,它保存应用程序的全部数据。我正在尝试在此 DataManager class 上实现 Codable 协议)
let child1 = Child1(child1Value: 1, baseValue: "Child1Value_Base")
let child2 = Child2(child2Value: 2, baseValue: "Child2Value_Base")
let dataManager = DataManager(bases: [])
dataManager.bases.append(child1 as Base)
dataManager.bases.append(child2 as Base)
我正在使用 JSONEncoder() 通过使用此代码将模型编码为数据。到目前为止一切正常。
let dataManagerData = try JSONEncoder().encode(dataManager)
print(String(data: dataManagerData, encoding: .utf8))
这是 json 编码后的样子
{
"bases":[{
"child1Value":1,
"baseValue":"Child1Value_Base"
},
{
"child2Value":2,
"baseValue":"Child2Value_Base"
}]
}
因此,当我尝试使用以下代码解码此 JSON 时,我只能将其解码到 Base(parent class) 级别,而不能解码到子级别。
let dataManager = try JSONDecoder().decode(DataManager.self, from: dataManagerData)
这就是我能从中得到的。
{
"bases":[{
"baseValue":"Child1Value_Base"
},
{
"baseValue":"Child2Value_Base"
}]
}
为了解决这个问题,我尝试使用这种方式手动解码,但 JSONDecoder 给了我 0 个 Bases。
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
private enum CodingKeys: String, CodingKey {
case bases
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
// I think decoder is trying to decode the bases object based on Child1 or Child2 class and it fail.
if let value = try? container.decode(Child1.self, forKey: .bases) {
bases.append(value as Base)
} else if let value = try? container.decode(Child2.self, forKey: .bases){
bases.append(value as Base)
}
} catch {
print(error)
}
}
}
所以我的问题是
- 如何根据各自的子 class 反序列化这个碱基数组并将它们添加到 DataManager?
- 在"init(from decoder: Decoder)"方法中有什么方法可以让我们获取键的值并一一遍历它们以解码到它们各自的class。
如果有人遇到同样的问题,我在下面找到了解决方案。
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
private enum CodingKeys: String, CodingKey {
case bases
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
var list = try container.nestedUnkeyedContainer(forKey: DataManager.CodingKeys.bases)
while !list.isAtEnd {
if let child1 = try? list.decode(Child1.self) {
bases.append(child1 as Base)
} else if let child2 = try? list.decode(Child2.self) {
bases.append(child2 as Base)
}
}
}
}
我正在使用 Codable 协议序列化和反序列化继承的 classes。我成功地将整个模型序列化为 JSON,但我在反序列化 JSON 时遇到了问题。这是我的数据结构。我的应用程序的某些部分像下面的示例一样工作,此时更改整个数据结构对我们来说工作量太大。
class Base: Codable {
let baseValue: String
init(baseValue :String) {
self.baseValue = baseValue
}
enum SuperCodingKeys: String, CodingKey {
case baseValue
}
func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: SuperCodingKeys.self)
try container.encode(baseValue, forKey: .baseValue)
}
}
class Child1: Base {
let child1Value: Int
init(child1Value: Int, baseValue: String) {
self.child1Value = child1Value
super.init(baseValue: baseValue)
}
private enum CodingKeys: String, CodingKey {
case child1Value
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.child1Value = try container.decode(Int.self, forKey: .child1Value)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(child1Value, forKey: .child1Value)
try super.encode(to: encoder)
}
}
class Child2: Base {
let child2Value: Int
init(child2Value: Int, baseValue: String) {
self.child2Value = child2Value
super.init(baseValue: baseValue)
}
private enum CodingKeys: String, CodingKey {
case child2Value
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.child2Value = try container.decode(Int.self, forKey: .child2Value)
try super.init(from: decoder)
}
override func encode(to encoder: Encoder) throws {
var container = encoder.container(keyedBy: CodingKeys.self)
try container.encode(child2Value, forKey: .child2Value)
try super.encode(to: encoder)
}
}
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
}
这是我为 DataManger 增加价值的方式(顺便说一句,在我的应用程序中,这是一个单例 class,它保存应用程序的全部数据。我正在尝试在此 DataManager class 上实现 Codable 协议)
let child1 = Child1(child1Value: 1, baseValue: "Child1Value_Base")
let child2 = Child2(child2Value: 2, baseValue: "Child2Value_Base")
let dataManager = DataManager(bases: [])
dataManager.bases.append(child1 as Base)
dataManager.bases.append(child2 as Base)
我正在使用 JSONEncoder() 通过使用此代码将模型编码为数据。到目前为止一切正常。
let dataManagerData = try JSONEncoder().encode(dataManager)
print(String(data: dataManagerData, encoding: .utf8))
这是 json 编码后的样子
{
"bases":[{
"child1Value":1,
"baseValue":"Child1Value_Base"
},
{
"child2Value":2,
"baseValue":"Child2Value_Base"
}]
}
因此,当我尝试使用以下代码解码此 JSON 时,我只能将其解码到 Base(parent class) 级别,而不能解码到子级别。
let dataManager = try JSONDecoder().decode(DataManager.self, from: dataManagerData)
这就是我能从中得到的。
{
"bases":[{
"baseValue":"Child1Value_Base"
},
{
"baseValue":"Child2Value_Base"
}]
}
为了解决这个问题,我尝试使用这种方式手动解码,但 JSONDecoder 给了我 0 个 Bases。
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
private enum CodingKeys: String, CodingKey {
case bases
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
// I think decoder is trying to decode the bases object based on Child1 or Child2 class and it fail.
if let value = try? container.decode(Child1.self, forKey: .bases) {
bases.append(value as Base)
} else if let value = try? container.decode(Child2.self, forKey: .bases){
bases.append(value as Base)
}
} catch {
print(error)
}
}
}
所以我的问题是
- 如何根据各自的子 class 反序列化这个碱基数组并将它们添加到 DataManager?
- 在"init(from decoder: Decoder)"方法中有什么方法可以让我们获取键的值并一一遍历它们以解码到它们各自的class。
如果有人遇到同样的问题,我在下面找到了解决方案。
class DataManager: Codable {
var bases: [Base] = []
init(bases: [Base]) {
self.bases = bases
}
private enum CodingKeys: String, CodingKey {
case bases
}
required init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
var list = try container.nestedUnkeyedContainer(forKey: DataManager.CodingKeys.bases)
while !list.isAtEnd {
if let child1 = try? list.decode(Child1.self) {
bases.append(child1 as Base)
} else if let child2 = try? list.decode(Child2.self) {
bases.append(child2 as Base)
}
}
}
}