使用 JsonConverter 进行 Json.NET 自定义序列化 - 如何获取“默认"行为 [英] Json.NET custom serialization with JsonConverter - how to get the "default" behavior

问题描述

我的类 DataType 有一个 JsonConverter.当在 Json 中使用纯字符串作为 DataType 类型的属性的值时，我想做一些特殊的处理.在值是完整"对象的情况下，我想做正常"反序列化.

I have a JsonConverter for my class DataType. I would like to do some special handling when plain string used in Json as the value of a property of type DataType. In the case where the value is a "full" object, I would like to do the "normal" deserialization.

这是我的尝试

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    if (reader.Value != null && reader.ValueType == typeof (string))
    {
        return someSpecialDataTypeInstance;
    }
    else if (reader.TokenType == JsonToken.StartObject)
    {
        DataType dataType = serializer.Deserialize<DataType>(reader);
        return dataType;
    }
    else
    {
        throw new JsonSerializationException();
    }
}

但这不起作用，因为这一行:DataType dataType = serializer.Deserialize(reader);导致无限递归.

But this doesn't work, because this line: DataType dataType = serializer.Deserialize(reader); causes infinite recursion.

这能以某种方式轻松完成吗?(无需手动逐个属性)

Could this be done somehow easily? (without the need to manually go property-by-property)

推荐答案

一种简单的方法是分配一个类的实例，然后使用 JsonSerializer.Populate(JsonReader, Object).这是在标准 CustomCreationConverter:

One easy way to do it is to allocate an instance of your class then use JsonSerializer.Populate(JsonReader, Object). This is the way it is done in the standard CustomCreationConverter<T>:

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    if (reader.Value != null && reader.ValueType == typeof(string))
    {
        return someSpecialDataTypeInstance;
    }
    else if (reader.TokenType == JsonToken.StartObject)
    {
        existingValue = existingValue ?? serializer.ContractResolver.ResolveContract(objectType).DefaultCreator();
        serializer.Populate(reader, existingValue);
        return existingValue;
    }
    else if (reader.TokenType == JsonToken.Null)
    {
        return null;
    }
    else
    {
        throw new JsonSerializationException();
    }
}

限制:

• 这不处理 TypeNameHandling 已启用，并且存在指定多态子类型的 "$type" 属性.

在这种情况下，您需要执行 带接口的 JsonConverter.

In this case you'll need to do some of the tricks use by JsonDerivedTypeConverer<T> in JsonConverter with Interface.

要反序列化的类型必须有一个无参数构造函数 可访问 Json.NET.如果不是，并且 existingValue 为 null，则需要通过 new DataType(arg1, arg2, ...) 手动构造它.

The type to be deserialized must have a parameterless constructor accessible to Json.NET. If not, and existingValue is null, it will be necessary to construct it manually, via new DataType(arg1, arg2, ...).

通过 PreserveReferencesHandling 保存参考不支持 a>.

Reference preservation via PreserveReferencesHandling is not supported.

有关处理这种情况的一种方法，请参阅如何根据json?.

For one approach to handle this situation see How can I choose what type to deserialize at runtime based on the structure of the json?.

示例小提琴.

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