如何使用 Json.Net 序列化/反序列化带有自定义键的字典？

Question

我有以下类，用作字典中的键：

    public class MyClass
    {
        private readonly string _property;

        public MyClass(string property)
        {
            _property = property;
        }

        public string Property
        {
            get { return _property; }
        }

        public override bool Equals(object obj)
        {
            MyClass other = obj as MyClass;
            if (other == null) return false;
            return _property == other._property;
        }

        public override int GetHashCode()
        {
            return _property.GetHashCode();
        }
    }

我正在运行的测试在这里：

    [Test]
    public void SerializeDictionaryWithCustomKeys()
    {
        IDictionary<MyClass, object> expected = new Dictionary<MyClass, object>();
        expected.Add(new MyClass("sth"), 5.2);
        JsonSerializerSettings jsonSerializerSettings = new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.All };
        string output = JsonConvert.SerializeObject(expected, Formatting.Indented, jsonSerializerSettings);
        var actual = JsonConvert.DeserializeObject<IDictionary<MyClass, object>>(output, jsonSerializerSettings);
        CollectionAssert.AreEqual(expected, actual);
    }

测试失败，因为 Json.Net 似乎在字典键上使用了ToString() 方法，而不是正确地序列化它们。上面测试的结果 json 是：

{
  "$type": "System.Collections.Generic.Dictionary`2[[RiskAnalytics.UnitTests.API.TestMarketContainerSerialisation+MyClass, RiskAnalytics.UnitTests],[System.Object, mscorlib]], mscorlib",
  "RiskAnalytics.UnitTests.API.TestMarketContainerSerialisation+MyClass": 5.2
}

这显然是错误的。我怎样才能让它工作？

Answer 1

这应该可以解决问题：

序列化：

JsonConvert.SerializeObject(expected.ToArray(), Formatting.Indented, jsonSerializerSettings);

通过调用expected.ToArray()，您正在序列化KeyValuePair<MyClass, object> 对象数组而不是字典。

反序列化：

JsonConvert.DeserializeObject<KeyValuePair<IDataKey, object>[]>(output, jsonSerializerSettings).ToDictionary(kv => kv.Key, kv => kv.Value);

在这里你反序列化数组，然后使用.ToDictionary(...) 调用检索字典。

我不确定输出是否符合您的期望，但肯定它通过了相等性断言。

Answer 2

Grx70 的回答很好 - 只是在这里添加一个替代解决方案。我在一个 Web API 项目中遇到了这个问题，我没有调用 SerializeObject，而是允许序列化自动发生。

这个基于Brian Rogers' answer to a similar question 的自定义JsonConverter 对我有用：

public class DeepDictionaryConverter : JsonConverter
{
    public override bool CanConvert(Type objectType)
    {
        return (typeof(IDictionary).IsAssignableFrom(objectType) ||
                TypeImplementsGenericInterface(objectType, typeof(IDictionary<,>)));
    }

    private static bool TypeImplementsGenericInterface(Type concreteType, Type interfaceType)
    {
        return concreteType.GetInterfaces()
               .Any(i => i.IsGenericType && i.GetGenericTypeDefinition() == interfaceType);
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        Type type = value.GetType();
        IEnumerable keys = (IEnumerable)type.GetProperty("Keys").GetValue(value, null);
        IEnumerable values = (IEnumerable)type.GetProperty("Values").GetValue(value, null);
        IEnumerator valueEnumerator = values.GetEnumerator();

        writer.WriteStartArray();
        foreach (object key in keys)
        {
            valueEnumerator.MoveNext();

            writer.WriteStartArray();
            serializer.Serialize(writer, key);
            serializer.Serialize(writer, valueEnumerator.Current);
            writer.WriteEndArray();
        }
        writer.WriteEndArray();
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

在我的例子中，我在一个类上序列化一个Dictionary<MyCustomType, int> 属性，其中MyCustomType 具有Name 和Id 之类的属性。结果如下：

...
"dictionaryProp": [
    [
      {
        "name": "MyCustomTypeInstance1.Name",
        "description": null,
        "id": null
      },
      3
    ],
    [
      {
        "name": "MyCustomTypeInstance2.Name",
        "description": null,
        "id": null
      },
      2
    ]
]
...

Answer 3

使用自定义 JsonConverter 的更简单、完整的解决方案

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

public class CustomDictionaryConverter<TKey, TValue> : JsonConverter
{
    public override bool CanConvert(Type objectType) => objectType == typeof(Dictionary<TKey, TValue>);

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        => serializer.Serialize(writer, ((Dictionary<TKey, TValue>)value).ToList());

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        => serializer.Deserialize<KeyValuePair<TKey, TValue>[]>(reader).ToDictionary(kv => kv.Key, kv => kv.Value);
}

用法：

[JsonConverter(typeof(CustomDictionaryConverter<KeyType, ValueType>))]
public Dictionary<KeyType, ValueType> MyDictionary;