JSONException:type java.lang.String cannot be converted to JSONArray

Question

I am trying to fetch data from 000webhost server into my xamarin.android application. connection of php mysqldatabase is working good but I am getting JSONException in one of my classes shown below.

DataPhraser.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Java.Lang;
using Org.Json;
using Object = Java.Lang.Object;
using String = System.String;

namespace database_test.database.mySQL
{
    class DataPhraser : AsyncTask
    {
        Context c;
        private Spinner sp;
        private String jsonData;
        JavaList<string> Universities = new JavaList<string>();
        private ProgressDialog pd;

        public DataPhraser(Context c, Spinner sp, string jsonData)
        {
            this.c = c;
            this.sp = sp;
            this.jsonData = jsonData;
        }


        protected override void OnPreExecute()
        {
            base.OnPreExecute();

            pd = new ProgressDialog(c);
            pd.SetTitle("Parse Data");
            pd.SetMessage("Parsing Data..... Please Wait");
            pd.Show();
        }

        protected override Object DoInBackground(params Object[] @params)
        {
            //throw new NotImplementedException();
            return this.ParseData();
        }

        protected override void OnPostExecute(Object result)
        {
            base.OnPostExecute(result);

            pd.Dismiss();

            if (Integer.ParseInt(result.ToString()) == 0)
            {
                Toast.MakeText(c, "unable to Prase", ToastLength.Short).Show();
            }
            else
            {
                ArrayAdapter<string> adapter = new ArrayAdapter<string>(c, Android.Resource.Layout.SimpleListItem1, Universities);
                sp.Adapter = adapter;

                sp.ItemSelected += sp_ItemSelected;
            }

        }

        private void sp_ItemSelected(object sender, AdapterView.ItemSelectedEventArgs e)
        {
            Toast.MakeText(c, Universities[e.Position], ToastLength.Short).Show();
        }

         private int ParseData()
        {

            try
            {
                JSONArray ja = new JSONArray(jsonData);
                JSONObject jo = null;

                Universities.Clear();

                for (int i = 0; i < ja.Length(); i++)
                {
                    jo = ja.GetJSONObject(i);

                    String name = jo.GetString("Country");

                    Universities.Add(name);

                }

                return 1;
            }
            catch (System.Exception e)
            {
                Console.WriteLine(e);
            }

            return 0;

        }
    }
}

I am getting error at " JSONArray ja = new JSONArray(jsonData)" this point of the code.

Mysqldatabase is

What is the value of jsonData when you get the exception?

holly_cheng
– holly_cheng

2019-10-18 19:59:40 +00:00
Commented Oct 18, 2019 at 19:59 — holly_cheng
– holly_cheng, Commented Oct 18, 2019 at 19:59

Jessie Zhang -MSFT · Accepted Answer · 2019-10-21 07:33:24Z

According to your gson, you can try to use Newtonsoft.Json Nuget ,for example:

namespace QuickType
{
using System;
using System.Collections.Generic;

using System.Globalization;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

public partial class Welcome
{
    [JsonProperty("Options")]
    public Option[] Options { get; set; }
}

public partial class Option
{
    [JsonProperty("ID")]
    public long Id { get; set; }

    [JsonProperty("University Name")]
    public string UniversityName { get; set; }

    [JsonProperty("Country")]
    public string Country { get; set; }

    [JsonProperty("Course")]
    public string Course { get; set; }

    [JsonProperty("Field of Study")]
    public string FieldOfStudy { get; set; }

    [JsonProperty("Course Language")]
    public string CourseLanguage { get; set; }

    [JsonProperty("Type of Institution")]
    public string TypeOfInstitution { get; set; }
}

public partial class Welcome
{
    public static Welcome FromJson(string json) => JsonConvert.DeserializeObject<Welcome>(json, QuickType.Converter.Settings);
}

public static class Serialize
{
    public static string ToJson(this Welcome self) => JsonConvert.SerializeObject(self, QuickType.Converter.Settings);
}

internal static class Converter
{
    public static readonly JsonSerializerSettings Settings = new JsonSerializerSettings
    {
        MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
        DateParseHandling = DateParseHandling.None,
        Converters =
        {
            new IsoDateTimeConverter { DateTimeStyles = 
             DateTimeStyles.AssumeUniversal }
        },
    };
 }
}

For more details, you can check: https://app.quicktype.io/#l=cs&r=json2csharp

Note: you can just copy your json string to the left part of above link, then it will convert the json into relative data models.

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