Json.net 自定义枚举转换器 [英] Json.net Custom enum converter

问题描述

我目前正在使用 Json.net 在我的应用程序中使用 json.我使用的 API 向我发送了一个特定的枚举字符串格式，例如:

I'm currently using Json.net to consume json in my app. The API I use send me a specific string format for enum for example:

对于类型为 TemperatureType 且值为 fahrenheit, Celcius

For an enum of type TemperatureType with values fahrenheit, Celcius

json 值为:{"result":["TemperatureType_fahrenheit","TemperatureType_Celcius"]}

我想用一个转换器直接管理它得到一个 IList 但也适用于其他枚举类型.

I would like to use a converter to directly manage it to get an IList<TemperatureType> but also working for other enum types.

有人有想法吗?

我尝试使用自定义 JsonConverter :

I've try to use a custom JsonConverter :

  if (reader.TokenType == JsonToken.String && reader.Value != null)
  {
      string value = reader.Value.ToString();
      var splitValues = value.Split('_');
      if (splitValues.Length == 2)
      {
         var type = Type.GetType(splitValues[0]);
         return Enum.Parse(type, splitValues[1]);
      }
  }

问题是 GetType 属性，因为我没有得到指示所需类型的参数，也没有命名空间

The problem is the GetType Property because I haven't got parameters indicating the desired type and no namespace

推荐答案

枚举类型是 ReadJson.但是，有几点:

The enum type is the objectType argument to ReadJson. However, a few points:

1. 您需要处理可为空的枚举类型.
2. 您需要处理[Flag] 枚举.Json.NET 将这些写为逗号分隔的值列表.
3. 您需要处理枚举值无效的情况.当 StringEnumConverter.AllowIntegerValues == true 时，Json.NET 将这些写为数值，否则抛出异常.

1. You need to handle nullable enum types.
2. You need to handle [Flag] enumerations. Json.NET writes these as comma-separated lists of values.
3. You need to handle the case of an enum with an invalid value. Json.NET writes these as numeric values when StringEnumConverter.AllowIntegerValues == true and throws an exception otherwise.

这是<的子类code>StringEnumConverter 通过调用基类然后在适当的时候添加或删除类型前缀来处理这些情况:

Here is a subclass of StringEnumConverter that handles these cases by calling the base class then adding or removing the type prefix when appropriate:

public class TypePrefixEnumConverter : StringEnumConverter
{
    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        bool isNullable = (Nullable.GetUnderlyingType(objectType) != null);
        Type enumType = (Nullable.GetUnderlyingType(objectType) ?? objectType);
        if (!enumType.IsEnum)
            throw new JsonSerializationException(string.Format("type {0} is not a enum type", enumType.FullName));
        var prefix = enumType.Name + "_";

        if (reader.TokenType == JsonToken.Null)
        {
            if (!isNullable)
                throw new JsonSerializationException();
            return null;
        }

        // Strip the prefix from the enum components (if any).
        var token = JToken.Load(reader);
        if (token.Type == JTokenType.String)
        {
            token = (JValue)string.Join(", ", token.ToString().Split(',').Select(s => s.Trim()).Select(s => s.StartsWith(prefix) ? s.Substring(prefix.Length) : s).ToArray());
        }

        using (var subReader = token.CreateReader())
        {
            while (subReader.TokenType == JsonToken.None)
                subReader.Read();
            return base.ReadJson(subReader, objectType, existingValue, serializer); // Use base class to convert
        }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var array = new JArray();
        using (var tempWriter = array.CreateWriter())
            base.WriteJson(tempWriter, value, serializer);
        var token = array.Single();

        if (token.Type == JTokenType.String && value != null)
        {
            var enumType = value.GetType();
            var prefix = enumType.Name + "_";
            token = (JValue)string.Join(", ", token.ToString().Split(',').Select(s => s.Trim()).Select(s => (!char.IsNumber(s[0]) && s[0] != '-') ? prefix + s : s).ToArray());
        }

        token.WriteTo(writer);
    }
}

然后，您可以在任何可以使用它的地方使用它StringEnumConverter，例如:

Then, you can use it wherever you could use StringEnumConverter, for instance:

        var settings = new JsonSerializerSettings { Converters = new JsonConverter[] { new TypePrefixEnumConverter() } };
        var json = JsonConvert.SerializeObject(myClass, Formatting.Indented, settings);

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