无法解析 codable 中的数据。我能够获取数据，但是一旦我使用解码功能，我就会出错

Question

我无法使用 decodable 解析数据。我能够获取数据但无法使用可解码函数对其进行解析。它说

unresolved identifier 'data' in that function.

试了各种方法还是不行

import UIKit    
import PlaygroundSupport    

PlaygroundPage.current.needsIndefiniteExecution = true

var str = "Hello, playground"

struct category : Codable {
    let success: Bool
    let list: [List]
    let slide: [String]
}

// MARK: - List
struct List: Codable {
    let id, categoryName: String
    let subcategory: [Subcategory]
}

// MARK: - Subcategory
struct Subcategory: Codable {
    let subCategoryID: SubCategoryID
    let subCategoryName, categoryID: String
    let banner: String

    enum CodingKeys: String, CodingKey {
        case subCategoryID = "sub_category_id"
        case subCategoryName = "sub_category_name"
        case categoryID = "category_id"
        case banner
    }
}

enum SubCategoryID: Codable {
case integer(Int)
case string(String)

init(from decoder: Decoder) throws {
    let container = try decoder.singleValueContainer()
    if let x = try? container.decode(Int.self) {
        self = .integer(x)
        return
    }
    if let x = try? container.decode(String.self) {
        self = .string(x)
        return
    }
    throw DecodingError.typeMismatch(SubCategoryID.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for SubCategoryID"))
}

func encode(to encoder: Encoder) throws {
    var container = encoder.singleValueContainer()
    switch self {
    case .integer(let x):
        try container.encode(x)
    case .string(let x):
        try container.encode(x)
    }

    let session = URLSession(configuration: .default)
    var datatask : URLSessionDataTask?
    let url = "http://comus.in/co/webservice/getCategoryList.php"
    var items = [URLQueryItem]()
    var myURL = URLComponents(string: url)
    let param = ["vendorId":"32"]
    for (key,value) in param {
        items.append(URLQueryItem(name: key, value: value))
    }
    myURL?.queryItems = items
    let request =  URLRequest(url: (myURL?.url)!)

    datatask = session.dataTask(with: request, completionHandler: {data, response, error in
        if error == nil {
            let receivedData = try? JSONSerialization.jsonObject(with: data!, options: []) as! [String: Any]
            print(receivedData!)
            let listings = try? JSONDecoder().decode(List.self , from: data)
            if let listings = listings{

            }
        }

    })
    datatask?.resume()
}

}

Answer 1

这是一个简单的语法错误。因为您在 decode 函数中的 data 之后错过了 !。另外正如@Joakim Danielson 在评论中建议的那样，当您不知道发生了什么时，不要 try? 。所以改变这个：

let listings = try? JSONDecoder().decode(List.self , from: data)
if let listings = listings{

}

对此：

do {
    let listings = try JSONDecoder().decode(List.self , from: data!)
    print(listings)
} catch {
    print(error)
}

无法解析 codable 中的数据。我能够获取数据，但是一旦我使用解码功能，我就会出错

Not able to parse data in codable. I am able to fetch data but some how once I use decode function I get error

swift

codable