自定义 jsonConverter的问题记录

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

namespace ConsoleApplication1
{
    public class A
    {
        public string Title = "A Title";

        [JsonConverter(typeof(ConsoleApplication1.Program.custConverter))]
        public List<answerBase> baseAnswerList = new List<answerBase>();
    }

    public class answerA : answerBase
    {
        public List<int> value = new List<int>() { 1, 2, 3 };
    }

    public class answerB : answerBase
    {
        public List<string> Correct = new List<string>() { "1111", "2222" };
        public List<string> Incorrect = new List<string>() { "3333", "4444" };
    }

    class Program
    {
        static void Main(string[] args)
        {
            JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings();
            jsonSerializerSettings.TypeNameHandling = TypeNameHandling.Objects;

            var test1 = new A();

            test1.baseAnswerList.Add(new answerA());

            var result = JsonConvert.SerializeObject(test1, jsonSerializerSettings);

            var test2 = new A();

            test2.baseAnswerList.Add(new answerB());

            var result2 = JsonConvert.SerializeObject(test2, jsonSerializerSettings);


            A a = (A)JsonConvert.DeserializeObject(result, jsonSerializerSettings);
            A a1 = (A)JsonConvert.DeserializeObject(result2, jsonSerializerSettings);

            List<A> testAList = new List<A>();

            testAList.Add(test1);
            testAList.Add(test2);

            var resultList = JsonConvert.SerializeObject(testAList, jsonSerializerSettings);

            var deserializeResult = JsonConvert.DeserializeObject(resultList, jsonSerializerSettings);
        }

        public class custConverter : JsonConverter
        {

            public override bool CanConvert(Type objectType)
            {
                return true;
            }

            public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
            {
                bool isError = false;
                try
                {
                    List<int> retValTest1 = new List<int>();
                    retValTest1 = (List<int>)serializer.Deserialize(reader, typeof(List<int>));
                    var t1 = new List<answerBase>();
                    var a1 = new answerA();
                    a1.value = retValTest1;
                    t1.Add(a1);

                    return t1;
                }
                catch
                {
                    isError = true;
                }

                if (isError)
                {
                    try
                    {
                        var retVal = new List<answerB>();
                        retVal = (List<answerB>)serializer.Deserialize(reader, typeof(List<answerB>));
                        var t = new List<answerBase>();

                        foreach (var item in retVal)
                        {
                            t.Add(new answerB()
                            {
                                Correct = item.Correct.Distinct().ToList(),
                                Incorrect = item.Incorrect.Distinct().ToList()
                            });
                        }

                        return t;
                    }
                    catch
                    {
                        isError = true;

                    }
                }
                return null;
            }
            //public override bool CanRead
            //{
            //    get { return false; }
            //}
            public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
            {
                if (value == null)
                {
                    writer.WriteNull();
                    return;
                }
                bool bValue = false;

                answerBase temp = new answerBase();
                if (((List<answerBase>)value).Count() > 0)
                {
                    temp = ((List<answerBase>)value).First();
                    bValue = temp is answerA;
                }

                if (bValue)
                {
                    var tempA = temp as answerA;

                    writer.WriteStartArray();

                    foreach (var item in tempA.value)
                    {
                        writer.WriteValue(item);
                    }
                    writer.WriteEndArray();

                }
                else
                {
                    JToken t = JToken.FromObject(value);
                    t.WriteTo(writer);
                }
            }
        }
    }
}