Json.NET如何覆盖通过属性定义自定义JsonConverter的类型的序列化？

Question

我试图使用Json.NET和自定义JsonConverter对象反序列化一个类.该类当前使用JsonConverterAttribute为默认序列化定义转换器.我需要通过传入自定义转换器来进行自定义反序列化.但是,反序列化似乎仍然使用默认转换器.如何让Json.NET更喜欢我的自定义转换器？

以下是一些演示此问题的示例代码.我正在使用NewtonSoft.Json 4.5.11:

void Main()
{
    JsonConvert.DeserializeObject<Foo>("{}"); // throws "in the default converter"
    var settings = new JsonSerializerSettings { Converters = new[] { new CustomConverter() } };
    JsonConvert.DeserializeObject<Foo>("{}", settings); // still throws "in the default converter" :-/
}

[JsonConverter(typeof(DefaultConverter))]
public class Foo {
}

public class DefaultConverter : JsonConverter {
    public override bool CanConvert(Type objectType)
    {
        return typeof(Foo).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new Exception("in the default converter!");
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new Exception("in the default converter!");
    }
}

public class CustomConverter : JsonConverter {
    public override bool CanConvert(Type objectType)
    {
        return typeof(Foo).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new Exception("in the custom converter!");
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new Exception("in the custom converter!");
    }
}

Answer 1

您需要使用自定义合同解析程序.仅当未为该类型指定转换器时,默认合同解析程序才使用来自设置的转换器.

class CustomContractResolver : DefaultContractResolver
{
    protected override JsonConverter ResolveContractConverter (Type objectType)
    {
        if (typeof(Foo).IsAssignableFrom(objectType))
            return null; // pretend converter is not specified
        return base.ResolveContractConverter(objectType);
    }
}

用法:

JsonConvert.DeserializeObject<Foo>("{}", new JsonSerializerSettings {
    ContractResolver = new CustomContractResolver(),
    Converters = new[] { new CustomConverter() },
});