C＃无法反序列化当前的JSON对象

Question

Trying to get JSON data from ThingSpeak however getting the above error, works well with JSON placeholder as the URL.

Here is my main cs code:

namespace Drip
{
    public class Feed
    {
        public DateTime Created_at { get; set; }
        public int Entry_id { get; set; }
        public string Field1 { get; set; }
    }

    public partial class DripPage : TabbedPage
    {
        private const string Url = "https://thingspeak.com/channels/301726/field/1.json";
        private HttpClient _client = new HttpClient();
        private ObservableCollection<Feed> _data;

        public DripPage()
        {
            InitializeComponent();
        }

        protected override async void OnAppearing()
        {
            var content = await _client.GetStringAsync(Url);
            var data = JsonConvert.DeserializeObject<List<Feed>>(content);

            _data = new ObservableCollection<Feed>(data);
            postsListView.ItemsSource = _data;
            base.OnAppearing();
        }

Here is my JSON:

{
  "channel": {
    "id": 301726,
    "name": "Testing ESP8266",
    "description": "Water meter pulse count",
    "latitude": "0.0",
    "longitude": "0.0",
    "field1": "Water Pulse",
    "created_at": "2017-07-12T12:19:38Z",
    "updated_at": "2017-09-26T08:41:17Z",
    "elevation": "54",
    "last_entry_id": 151
  },
  "feeds": [
    {
      "created_at": "2017-08-15T13:14:28Z",
      "entry_id": 52,
      "field1": "13.00\r\n\r\n"
    },
    {
      "created_at": "2017-08-15T13:14:44Z",
      "entry_id": 53,
      "field1": "13.00\r\n\r\n"
    },
    {
      "created_at": "2017-08-15T13:14:59Z",
      "entry_id": 54,
      "field1": "13.00\r\n\r\n"
    }
  ]
}

Answer 1

The returned json is not an array, so it can't be deserialized as a List<Feed> , hence an exception is thrown. It is an object , and one of that object's members is the array that you are interested in. The backing C# class to deserialize should have the following members:

public class RootObject
{
    public Channel channel { get; set; }
    public List<Feed> feeds { get; set; }
}

public class Channel
{
    public int id { get; set; }
    public string name { get; set; }
    public string description { get; set; }
    public string latitude { get; set; }
    public string longitude { get; set; }
    public string field1 { get; set; }
    public DateTime created_at { get; set; }
    public DateTime updated_at { get; set; }
    public string elevation { get; set; }
    public int last_entry_id { get; set; }
}

public class Feed
{
    public DateTime created_at { get; set; }
    public int entry_id { get; set; }
    public string field1 { get; set; }
}

Instead of deserializing to a List<Feed> , you would deserialize to a RootObject (or whatever you choose to call it):

var data = JsonConvert.DeserializeObject<RootObject>(content);
_data = new ObservableCollection<Feed>(data.feeds);

Answer 2

try this maybe it will work fine for you first: place this code on your activity and instanciate all var;you will create a javalist to deserialize your json, then you will the method webclient to get your json, then you will use the method runonuithread to excute the process in background.

articles = new JavaList<RootObject>();
        mWebClient = new WebClient();
        mUrl = new Uri(urlAddress);
        mWebClient.DownloadDataAsync("https://thingspeak.com/channels/301726/field/1.json");
        mWebClient.DownloadDataCompleted += MWebClient_DownloadDataCompleted;

second: the method mWebClient.DownloadDataCompleted will generate this :

private void MWebClient_DownloadDataCompleted(object sender, DownloadDataCompletedEventArgs e)
    {
        RunOnUiThread(() =>
        {
            try
            {
                string json = Encoding.UTF8.GetString(e.Result);
                articles = JsonConvert.DeserializeObject<JavaList<RootObject>>(json);
                mAdapter = new ArticleAdapterCostum(this, articles);
                mListView.Adapter = mAdapter;
            }
            catch (Exception exception)
            {
                Toast.MakeText(this, " Vueillez verifier votre connexion a internet puis reessayer ", ToastLength.Short).Show();
            }
        });
    }

don't forget to create a costum adapter to your listview.