当键根据用户输入更改时,如何从 json 解码变量?
How to decode variable from json when key is changing according to user input?
我正在尝试使用 Swift 中的 JSONDecoder()
解析来自 CoinmarketCap 的一些 JSON 响应 4。但问题是来自 [=23 的响应=] 根据用户输入而变化。例如,如果用户想要欧元价格,输出如下:
[
{
"price_eur": "9022.9695444"
}
]
但如果用户想要以英镑为单位的价格:
[
{
"price_gbp": "7906.8032145"
}
]
所以问题是,如果变量(json 键)名称发生变化,我应该如何制作继承自 Decodable
的结构?
如果您有少量可能的键,您可以执行以下操作
struct Price: Decodable {
var value: String
enum CodingKeys: String, CodingKey {
case price_eur
case price_gbp
case price_usd
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
value = try container.decode(String.self, forKey: .price_eur)
} catch {
do {
value = try container.decode(String.self, forKey: .price_gbp)
} catch {
value = try container.decode(String.self, forKey: .price_usd)
}
}
}
}
let data = try! JSONSerialization.data(withJSONObject: ["price_gbp": "10.12"], options: [])
let price = try JSONDecoder().decode(Price.self, from: data)
否则,您将需要手动解析数据。
您可以通过为您的结构创建自定义 init(from:)
方法来解码动态密钥,然后使用两组编码密钥,一个 enum
包含编译时已知的所有密钥,另一个struct
您使用用户输入(包含货币名称)生成的动态密钥进行初始化。
在您的自定义 init(from:)
方法中,您只需使用各自的密钥对每个 属性 进行解码。
let chosenCurrency = "gbp"
struct CurrencyResponse: Decodable {
let name:String
let symbol:String
let price:String
private static var priceKey:String {
return "price_\(chosenCurrency)"
}
private enum SimpleCodingKeys: String, CodingKey {
case name, symbol
}
private struct PriceCodingKey : CodingKey {
var stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
}
var intValue: Int?
init?(intValue: Int) {
return nil
}
}
init(from decoder:Decoder) throws {
let values = try decoder.container(keyedBy: SimpleCodingKeys.self)
name = try values.decode(String.self, forKey: .name)
symbol = try values.decode(String.self, forKey: .symbol)
let priceValue = try decoder.container(keyedBy: PriceCodingKey.self)
price = try priceValue.decode(String.self, forKey: PriceCodingKey(stringValue:CurrencyResponse.priceKey)!)
}
}
do {
let cryptoCurrencies = try JSONDecoder().decode([CurrencyResponse].self, from: priceJSON.data(using: .utf8)!)
} catch {
print(error)
}
测试JSON:
let priceJSON = """
[
{
"id": "bitcoin",
"name": "Bitcoin",
"symbol": "BTC",
"rank": "1",
"price_\(chosenCurrency)": "573.137",
"price_btc": "1.0",
"24h_volume_\(chosenCurrency)": "72855700.0",
"market_cap_\(chosenCurrency)": "9080883500.0",
"available_supply": "15844176.0",
"total_supply": "15844176.0",
"percent_change_1h": "0.04",
"percent_change_24h": "-0.3",
"percent_change_7d": "-0.57",
"last_updated": "1472762067"
},
{
"id": "ethereum",
"name": "Ethereum",
"symbol": "ETH",
"rank": "2",
"price_\(chosenCurrency)": "12.1844",
"price_btc": "0.021262",
"24h_volume_\(chosenCurrency)": "24085900.0",
"market_cap_\(chosenCurrency)": "1018098455.0",
"available_supply": "83557537.0",
"total_supply": "83557537.0",
"percent_change_1h": "-0.58",
"percent_change_24h": "6.34",
"percent_change_7d": "8.59",
"last_updated": "1472762062"
}
]
"""
我正在尝试使用 Swift 中的 JSONDecoder()
解析来自 CoinmarketCap 的一些 JSON 响应 4。但问题是来自 [=23 的响应=] 根据用户输入而变化。例如,如果用户想要欧元价格,输出如下:
[
{
"price_eur": "9022.9695444"
}
]
但如果用户想要以英镑为单位的价格:
[
{
"price_gbp": "7906.8032145"
}
]
所以问题是,如果变量(json 键)名称发生变化,我应该如何制作继承自 Decodable
的结构?
如果您有少量可能的键,您可以执行以下操作
struct Price: Decodable {
var value: String
enum CodingKeys: String, CodingKey {
case price_eur
case price_gbp
case price_usd
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
do {
value = try container.decode(String.self, forKey: .price_eur)
} catch {
do {
value = try container.decode(String.self, forKey: .price_gbp)
} catch {
value = try container.decode(String.self, forKey: .price_usd)
}
}
}
}
let data = try! JSONSerialization.data(withJSONObject: ["price_gbp": "10.12"], options: [])
let price = try JSONDecoder().decode(Price.self, from: data)
否则,您将需要手动解析数据。
您可以通过为您的结构创建自定义 init(from:)
方法来解码动态密钥,然后使用两组编码密钥,一个 enum
包含编译时已知的所有密钥,另一个struct
您使用用户输入(包含货币名称)生成的动态密钥进行初始化。
在您的自定义 init(from:)
方法中,您只需使用各自的密钥对每个 属性 进行解码。
let chosenCurrency = "gbp"
struct CurrencyResponse: Decodable {
let name:String
let symbol:String
let price:String
private static var priceKey:String {
return "price_\(chosenCurrency)"
}
private enum SimpleCodingKeys: String, CodingKey {
case name, symbol
}
private struct PriceCodingKey : CodingKey {
var stringValue: String
init?(stringValue: String) {
self.stringValue = stringValue
}
var intValue: Int?
init?(intValue: Int) {
return nil
}
}
init(from decoder:Decoder) throws {
let values = try decoder.container(keyedBy: SimpleCodingKeys.self)
name = try values.decode(String.self, forKey: .name)
symbol = try values.decode(String.self, forKey: .symbol)
let priceValue = try decoder.container(keyedBy: PriceCodingKey.self)
price = try priceValue.decode(String.self, forKey: PriceCodingKey(stringValue:CurrencyResponse.priceKey)!)
}
}
do {
let cryptoCurrencies = try JSONDecoder().decode([CurrencyResponse].self, from: priceJSON.data(using: .utf8)!)
} catch {
print(error)
}
测试JSON:
let priceJSON = """
[
{
"id": "bitcoin",
"name": "Bitcoin",
"symbol": "BTC",
"rank": "1",
"price_\(chosenCurrency)": "573.137",
"price_btc": "1.0",
"24h_volume_\(chosenCurrency)": "72855700.0",
"market_cap_\(chosenCurrency)": "9080883500.0",
"available_supply": "15844176.0",
"total_supply": "15844176.0",
"percent_change_1h": "0.04",
"percent_change_24h": "-0.3",
"percent_change_7d": "-0.57",
"last_updated": "1472762067"
},
{
"id": "ethereum",
"name": "Ethereum",
"symbol": "ETH",
"rank": "2",
"price_\(chosenCurrency)": "12.1844",
"price_btc": "0.021262",
"24h_volume_\(chosenCurrency)": "24085900.0",
"market_cap_\(chosenCurrency)": "1018098455.0",
"available_supply": "83557537.0",
"total_supply": "83557537.0",
"percent_change_1h": "-0.58",
"percent_change_24h": "6.34",
"percent_change_7d": "8.59",
"last_updated": "1472762062"
}
]
"""