JSON.NET中基于属性的类型解析

Question

是否可以使用JSON.NET基于JSON对象的属性覆盖类型解析？基于现有的API,看起来我需要一种接受JsonPropertyCollection并返回Type要创建的方法.

注意:我知道TypeNameHandling属性,但它添加了一个$type属性.我无法控制源JSON.

Answer 1

看起来这是通过创建自定义JsonConverter并JsonSerializerSettings.Converters在反序列化之前添加它来处理的.

nonplus在Codeplex 的JSON.NET讨论板上留下了一个方便的样本.我已经修改了示例以返回自定义Type并推迟到默认创建机制,而不是在现场创建对象实例.

abstract class JsonCreationConverter<T> : JsonConverter
{
    /// <summary>
    /// Create an instance of objectType, based properties in the JSON object
    /// </summary>
    protected abstract Type GetType(Type objectType, JObject jObject);

    public override bool CanConvert(Type objectType)
    {
        return typeof(T).IsAssignableFrom(objectType);
    }

    public override object ReadJson(JsonReader reader, Type objectType, 
        object existingValue, JsonSerializer serializer)
    {
        JObject jObject = JObject.Load(reader);

        Type targetType = GetType(objectType, jObject);

        // TODO: Change this to the Json.Net-built-in way of creating instances
        object target = Activator.CreateInstance(targetType);

        serializer.Populate(jObject.CreateReader(), target);

        return target;
    }
}

以下是示例用法(也如上所述更新):

class VehicleConverter : JsonCreationConverter<Vehicle>
{
    protected override Type GetType(Type objectType, JObject jObject)
    {
        var type = (string)jObject.Property("Type");
        switch (type)
        {
            case "Car":
                return typeof(Car);
            case "Bike":
                return typeof(Bike);
        }

        throw new ApplicationException(String.Format(
            "The given vehicle type {0} is not supported!", type));
    }
}