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
当您需要将单个结构体、枚举或类从String
转换为Float
时,请使用此策略。
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)
#2. 使用中间模型
如果你的 JSON 中有许多嵌套键,或者需要将许多键(例如从 String
转换为 Float
)转换为其他类型,则可以使用此策略。
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
}
}
使用方法:
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)
#3. 使用 KeyedDecodingContainer
扩展方法
如果在应用程序中将一些 JSON 键的类型转换为您模型属性类型(例如,从String
到Float
)是一个常见模式,请使用此策略。
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"
}
}
使用方法:
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)