如何快速訪問一項結構

我來自 javascript，現在我正在為 swift 學習。我想列印我的 URLSession 回傳的一項，但我不知道該怎么做。

我的代碼：

import Foundation
import Dispatch

enum ServiceError: Error {
    case invalidURL
    case decodeFail(Error)
    case network(Error?)
}

struct Address: Codable {
    let zipcode: String
    let address: String
    let city: String
    let uf: String
    let complement: String?
    
    enum CodingKeys: String, CodingKey {
        case zipcode = "cep"
        case address = "logradouro"
        case city = "localidade"
        case uf
        case complement = "complemento"
    }
}

class Service {
    private let baseURL = "https://viacep.com.br/ws"
    
    func get(cep: String, callback: @escaping (Result<Any, ServiceError>) -> Void) {
     
        let path = "/\(cep)/json"
        guard let url = URL(string: baseURL   path) else {
            callback(.failure(.invalidURL))
            return
        }
        
        let task = URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data else {
                callback(.failure(.network(error)))
                return
            }

            guard let json: Address = try? JSONDecoder().decode(Address.self, from: data) else {
                return
            }
            callback(.success(json))
        }
        task.resume()
    }
}

do {
    let service = Service()
    service.get(cep: "1231234") { result in
        DispatchQueue.main.async {
            switch result {
            case let .failure(error):
                print(error)
            case let .success(data):
                print(data)
            }
        }
    }

}

這是我的回報：

地址（郵編：“12341231”，地址：“Teste”，城市：“Teste”，uf：“TE”，補碼：可選（“”））

我想要我的回報是這樣的：

print(data.zipcode)

Output: 12341231

uj5u.com熱心網友回復：

與 javascript 不同，Swift 是強型別的，所以Address從你的回傳型別func get(cep:...)，而不是Any.

請注意，在執行服務器請求時需要處理許多型別的錯誤。

錯誤可能意味著由于請求錯誤而無法解碼回應，例如 cep: "1231234" 的情況。如果您使用 cep:"01001000"，則不會出現錯誤，并且一切正常。

因此，我建議更新您的代碼（尤其是ServiceError），以應對您可能遇到的各種錯誤。

這是我用來測驗答案的代碼：

 let service = Service()
 // try also "01001000" for no errors
 service.get(cep: "1231234") { result in
     switch result {
     case let .failure(error):
         print("\n---> error: \(error)")
     case let .success(data):
         print("\n---> data: \(data)")
         print("---> zipcode: \(data.zipcode)")
     }
 }
 

和

class Service {
    private let baseURL = "https://viacep.com.br/ws"
    
    // here return Address, not Any
    func get(cep: String, callback: @escaping (Result<Address, ServiceError>) -> Void) {
     
        let path = "/\(cep)/json"
        guard let url = URL(string: baseURL   path) else {
            callback(.failure(.invalidURL))
            return
        }
        
        let task = URLSession.shared.dataTask(with: url) { data, response, error in
            guard let data = data else {
                callback(.failure(.network(error)))
                return
            }
            // this shows you what the server is really sending you
            print("\n---> data: \(String(data: data, encoding: .utf8)) \n")
            
            guard let httpResponse = response as? HTTPURLResponse else {
                callback(.failure(.apiError(reason: "Unknown")))
                return
            }
            
            switch httpResponse.statusCode {
            case 400: return callback(.failure(.apiError(reason: "Bad Request")))
            case 401: return callback(.failure(.apiError(reason: "Unauthorized")))
            case 403: return callback(.failure(.apiError(reason: "Resource forbidden")))
            case 404: return callback(.failure(.apiError(reason: "Resource not found")))
            case 405..<500: return callback(.failure(.apiError(reason: "client error")))
            case 500..<600: return callback(.failure(.apiError(reason: "server error")))
            default:
                callback(.failure(.apiError(reason: "Unknown")))
            }

            // here use a proper do/catch
            do {
                let address = try JSONDecoder().decode(Address.self, from: data)
                callback(.success(address))
            } catch {
                // could not be decoded as an Address.
                callback(.failure(.decodeFail(error)))
            }
        }
        task.resume()
    }
}

enum ServiceError: Error {
    case invalidURL
    case decodeFail(Error)
    case network(Error?)
    case apiError(reason: String) // <-- here
}

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