使用 Swift 5.1,您可以选择以下三种方式之一来解决您的问题。
#1。使用Decodable
init(from:)
初始化器
当您需要从 to 转换为单个结构、枚举或类时,请使用此String
策略Float
。
import Foundation
struct ExampleJson: Decodable {
var name: String
var age: Int
var taxRate: Float
enum CodingKeys: String, CodingKey {
case name, age, taxRate = "tax_rate"
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
name = try container.decode(String.self, forKey: CodingKeys.name)
age = try container.decode(Int.self, forKey: CodingKeys.age)
let taxRateString = try container.decode(String.self, forKey: CodingKeys.taxRate)
guard let taxRateFloat = Float(taxRateString) else {
let context = DecodingError.Context(codingPath: container.codingPath + [CodingKeys.taxRate], debugDescription: "Could not parse json key to a Float object")
throw DecodingError.dataCorrupted(context)
}
taxRate = taxRateFloat
}
}
用法:
import Foundation
let jsonString = """
{
"name": "Bob",
"age": 25,
"tax_rate": "4.25"
}
"""
let data = jsonString.data(using: String.Encoding.utf8)!
let decoder = JSONDecoder()
let exampleJson = try! decoder.decode(ExampleJson.self, from: data)
dump(exampleJson)
/*
prints:
▿ __lldb_expr_126.ExampleJson
- name: "Bob"
- age: 25
- taxRate: 4.25
*/
#2。使用中间模型
当您的 JSON 中有许多嵌套键或需要从 JSON 转换许多键(例如 fromString
到Float
)时,请使用此策略。
import Foundation
fileprivate struct PrivateExampleJson: Decodable {
var name: String
var age: Int
var taxRate: String
enum CodingKeys: String, CodingKey {
case name, age, taxRate = "tax_rate"
}
}
struct ExampleJson: Decodable {
var name: String
var age: Int
var taxRate: Float
init(from decoder: Decoder) throws {
let privateExampleJson = try PrivateExampleJson(from: decoder)
name = privateExampleJson.name
age = privateExampleJson.age
guard let convertedTaxRate = Float(privateExampleJson.taxRate) else {
let context = DecodingError.Context(codingPath: [], debugDescription: "Could not parse json key to a Float object")
throw DecodingError.dataCorrupted(context)
}
taxRate = convertedTaxRate
}
}
用法:
import Foundation
let jsonString = """
{
"name": "Bob",
"age": 25,
"tax_rate": "4.25"
}
"""
let data = jsonString.data(using: String.Encoding.utf8)!
let decoder = JSONDecoder()
let exampleJson = try! decoder.decode(ExampleJson.self, from: data)
dump(exampleJson)
/*
prints:
▿ __lldb_expr_126.ExampleJson
- name: "Bob"
- age: 25
- taxRate: 4.25
*/
#3。使用KeyedDecodingContainer
扩展方法
当从某些 JSON 键的类型转换为模型的属性类型(例如String
to Float
)时使用此策略是应用程序中的常见模式。
import Foundation
extension KeyedDecodingContainer {
func decode(_ type: Float.Type, forKey key: Key) throws -> Float {
if let stringValue = try? self.decode(String.self, forKey: key) {
guard let floatValue = Float(stringValue) else {
let context = DecodingError.Context(codingPath: codingPath, debugDescription: "Could not parse json key to a Float object")
throw DecodingError.dataCorrupted(context)
}
return floatValue
} else {
let doubleValue = try self.decode(Double.self, forKey: key)
return Float(doubleValue)
}
}
}
struct ExampleJson: Decodable {
var name: String
var age: Int
var taxRate: Float
enum CodingKeys: String, CodingKey {
case name, age, taxRate = "tax_rate"
}
}
用法:
import Foundation
let jsonString = """
{
"name": "Bob",
"age": 25,
"tax_rate": "4.25"
}
"""
let data = jsonString.data(using: String.Encoding.utf8)!
let decoder = JSONDecoder()
let exampleJson = try! decoder.decode(ExampleJson.self, from: data)
dump(exampleJson)
/*
prints:
▿ __lldb_expr_126.ExampleJson
- name: "Bob"
- age: 25
- taxRate: 4.25
*/