Swift3+URLSession+JSONSerializationで JSONなREST APIを叩いて表示まで

https://your-rest-api/items のレスポンスが以下の場合で。

サンプルJSON

{
      "Items": [
          {
              "title": "森田一義",
              "id": "big1",
          },
          {
              "title": "北野武",
              "id": "big2",
          },
          {
              "title": "明石家さんま",
              "id": "big3",
          }
      ]
  }

enum SerializationError: Error {
    case missing(String)
    case invalid(String, Any)
}

let url = URL(string: "https://your-rest-api/items")

let task = URLSession.shared.dataTask(with: url!) { data ,response ,error in

    if let data=data, let response=response{
        do{
            let json = try JSONSerialization.jsonObject(with: data, options: JSONSerialization.ReadingOptions.allowFragments) as! [String:Any]
             // すべてのitemにアクセスする
             for case let item in (json["Items"] as? [[String:Any]])!{
                    guard let title = item["title"] as? String else {
                        throw SerializationError.missing("title")
                    }
                    guard let id = item["id"] as? String else {
                        throw SerializationError.missing("id")
                    }
                    print(id + " : " + title)
                }
            } catch{
                print("Serialize Error.")
            }
        }else{
            print(error ?? " Error")
        }
    }