Parse universities from VK API

问题

I need to write to List<string> the list of universities. I already had written countries and cities to lists. But in universities data is represented a little bit different. There is {"response":[201, and I do not have any idea how to handle with it. I successfully got countries from here. And from here I need to write universities titles to a List<string>. This is code how did I got countries. The analogical code I used in cities. While trying to execute this line var universityRepository = new RootObject((int)universityInResponse["id"], (string)universityInResponse["title"]); I got an unhandled exception. The full code of the class:

public class GettingUniversity
{
    public static List<RootObject> listOfUniversitiesRoot = new List<RootObject>();//This List contains Id and Titles of universities
    public List<string> listOfUniversities = new List<string>();//list with names of the universities
    private string jsonString; //string for getting data from the url
    public async Task<List<RootObject>> FetchAsync(string url)
    {
        //getting data process goes here
        using (var httpClient = new System.Net.Http.HttpClient())
        {
            var stream = await httpClient.GetStreamAsync(url);
            StreamReader reader = new StreamReader(stream);
            jsonString = reader.ReadToEnd();
        }

        var responseUniversities = JArray.Parse(JObject.Parse(jsonString)["response"].ToString());//parsing data from jsonstring

        foreach (var universityInResponse in responseUniversities)//the foreach-loop
        {
            var universityRepository = new RootObject((int)universityInResponse["id"], (string)universityInResponse["title"]);
            //listOfUniversitiesRoot.Add(universityRepository);//adding to the list with names of the universities
            //listOfUniversities.Add(universityRepository.Title);
        }

        return listOfUniversitiesRoot;//returned list
    }

Properties are represented here:

namespace KoshelnykTestTask
{
    //Here I have set properties for FetchAsync(string url) to get countries and cities 
    public class RootObject
    {
        public int Id { get; set; }
        public string Title { get; set; }
        public RootObject(int Id, string Title)
        {
            this.Id = Id;
            this.Title = Title;
        }
    }
}

回答1:

Your problem is that the JSON returned contains an array that is polymorphic -- the first entry is an integer, and the remainder are objects containing university information:

{
   "response":[
      201,
      {
         "id":1096,
         "title":"КПИ им. И. Сикорского"
      },
      {
         "id":1135,
         "title":"НУФВСУ (бывш. КГИФК)"
      },
      {
         "id":1140,
         "title":"КГАВТ им. Конашевича-Сагайдачного"
      },

You need to filter the integer value before deserializing the objects, which can be done as follows:

var universityRepository  = JToken.Parse(jsonString)["response"]
    // Filter the integer value by selecting only objects
    .OfType<JObject>()
    // Deserialize each object to a RootObject
    .Select(o => o.ToObject<RootObject>())
    // Return in a List<RootObject>
    .ToList();

var listOfUniversities = universityRepository
    .Select(u => u.Title)
    .ToList();

Sample fiddle.

Note there seems to be no need to store these lists in static or class variables -- you can simply return them to the caller.

来源：https://stackoverflow.com/questions/42939991/parse-universities-from-vk-api

标签

json

api