json - 快速解析 JSON 并在数组中循环时出错

Question

我有一个返回 JSON 的 API，我想解析这个 JSON 并在我的应用程序中使用它。

我试过从这个获取方法:swift JSON login REST with post and get response example

代码:

func makeGetCall() {

    // Set up the URL request

    let todoEndpoint: String = "my link"

    guard let url = URL(string: todoEndpoint) else {

        print("Error: cannot create URL")

        return

    }

    let urlRequest = URLRequest(url: url)



    // set up the session

    let config = URLSessionConfiguration.default

    let session = URLSession(configuration: config)



    // make the request

    let task = session.dataTask(with: urlRequest) {

        (data, response, error) in

        // check for any errors

        guard error == nil else {

            print("error calling GET on /public/api/services")

            print(error!)

            return

        }

        // make sure we got data

        guard let responseData = data else {

            print("Error: did not receive data")

            return

        }

        // parse the result as JSON, since that's what the API provides

        do {

            guard let todo = try JSONSerialization.jsonObject(with: responseData, options: [])

                as? [String: Any] else {

                    print("error trying to convert data to JSON")

                    return

            }

            // now we have the todo

            // let's just print it to prove we can access it

            print("The todo is: " + todo.description)



            // the todo object is a dictionary

            // so we just access the title using the "title" key

            // so check for a title and print it if we have one

            guard let todoTitle = todo["name"] as? String else {

                print("Could not get todo title from JSON")

                return

            }

            print("The title is: " + todoTitle)

        } catch  {

            print("error trying to convert data to JSON")

            return

        }

    }

    task.resume()

}

我得到了一个输出:尝试将数据转换为 JSON 时出错。

我的 JSON 是:

[
  {
    "id": 1,
    "name": "Services 1",
    "description": "This is a description of Services 1. This is a description of Services 1 This is a description of Services 1. ",
    "created_at": null,
    "updated_at": null
  },
  {
    "id": 2,
    "name": "Services 2",
    "description": "This is a description of Services 2. This is a description of Services 2 This is a description of Services 2. ",
    "created_at": null,
    "updated_at": null
  }
]

为什么我在解析 JSON 时出错？

另外，如何循环数组并打印每一项？

例如:

service 1 description is: This is a description of Services 1. This is a description of Services 1 This is a description of Services 1.

service 2 description is: This is a description of Services 2. This is a description of Services 2 This is a description of Services 2.

Answer 1

请仔细阅读JSON。根对象显然是一个数组 ([])

guard let todos = try JSONSerialization.jsonObject(with: responseData) as? [[String: Any]] else {                    
       print("error trying to convert data to JSON")
       return
  }
  for todo in todos {
      print(todo["name"] as? String ?? "n/a")
  }

---

但是我建议使用Decodable 协议(protocol)。在类外声明这个结构

struct Service : Decodable {
    let id : Int
    let name, description : String
    let createdAt : String?
    let updatedAt : String?
}

并以这种方式解码 JSON

do {
   let decoder = JSONDecoder()
   decoder.keyDecodingStrategy = .convertFromSnakeCase
   let todos = try decoder.decode([Service].self, from: responseData)
   for todo in todos {
      print(todo.name)
   }

} catch { print(error) }

旁注:

行 guard let responseData = data else { 永远不会到达 else 子句。如果 error 是 nil——已经检查过了——那么可以保证 data 有一个值。