How can I generically deserialize PropertyInfo with Json.NET?

Question

I need to serialize many different objects with Json.NET. I really have no control over the objects being provided, so I'm generically serializing and de-serializing with TypeNameHandling.All.

However, some of these objects cannot be de-serialized. Specifically, I am getting some System.Reflection.RuntimePropertyInfo types. I'd like to handle these in a standardized fashion, as I am unaware of the target type at the time of de-serialization. Nor do I care, as long as the output object type is correct.

I've attempted a CustomCreationConverter typed to PropertyInfo that is defined in JsonSerializerSettings. However, even though CanConvert() is returning true, the CustomCreationConverter's ReadJson() is never utilized.

The end result is the same as if I had never used the CustomCreationConverter:

ISerializable type 'System.Reflection.RuntimePropertyInfo' does not have a valid constructor. To correctly implement ISerializable a constructor that takes SerializationInfo and StreamingContext parameters should be present.

I need the CustomCreationConverter to handle the ReadJson so that I can manually search for the PropertyInfo myself.

After more investigation, it appears that the Converters I am adding to the JsonSerializerSettings are not being utilized at all. If I use the DeserializeObject overload that includes the Type and collection of JsonConverter, the Converter will be utilized. I am unsure as to what the Converters supplied to the JsonSerializerSettings are used for, but I would expect they would work as I intend in this situation.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Runtime.Serialization.Formatters;
using System.Text;
using System.Threading.Tasks;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;
using Newtonsoft.Json.Linq;

namespace Json
{
    class Program
    {
        static void Main(string[] args)
        {
            var jsonSerializerSettings = new JsonSerializerSettings()
            {
                TypeNameHandling = TypeNameHandling.All,
                TypeNameAssemblyFormat = FormatterAssemblyStyle.Simple,
                Converters = new JsonConverter[] { new PropertyInfoConverter(), },
            };
            var propertyInfo = typeof(Test).GetProperty("Name");

            var serialized = JsonConvert.SerializeObject(propertyInfo, jsonSerializerSettings);
            var deserialized = JsonConvert.DeserializeObject(serialized, jsonSerializerSettings);
        }
    }

    public class Test
    {
        public string Name { get; set; }
    }

    public class PropertyInfoConverter : CustomCreationConverter<PropertyInfo>
    {
        public override bool CanConvert(Type objectType)
        {
            return typeof(PropertyInfo).IsAssignableFrom(objectType);
        }

        public override PropertyInfo Create(Type objectType)
        {
            return null;
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            return null; // This is never invoked, but is where I would attempt to find the PropertyInfo via Reflection searching.
        }
    }
}

Answer 1

Assuming the API you need to conform to must input/output a PropertyInfo object you can cut out the converter and use a new class to save only the information necessary to recreate the object.

private class PropertyInfoData
{
    public string TypeName
    {
        get;
        set;
    }

    public string PropertyName
    {
        get;
        set;
    }

    public static PropertyInfoData FromProperty(PropertyInfo p)
    {
        return new PropertyInfoData()
        {
            TypeName = p.DeclaringType.AssemblyQualifiedName,
            PropertyName = p.Name,
        };
    }

    public PropertyInfo ToProperty()
    {
        return Type.GetType(this.TypeName).GetProperty(this.PropertyName);
    }
}

Then you can de/serialize it like this:

var jsonSerializerSettings = new JsonSerializerSettings()
{
    TypeNameHandling = TypeNameHandling.All,
    TypeNameAssemblyFormat = FormatterAssemblyStyle.Simple,
    //Converters = new JsonConverter[] { new PropertyInfoConverter(), },
};
var propertyInfo = typeof(Test).GetProperty("Name");

var serialized = JsonConvert.SerializeObject(PropertyInfoData.FromProperty(propertyInfo), jsonSerializerSettings);
var deserialized = ((PropertyInfoData)JsonConvert.DeserializeObject(serialized, jsonSerializerSettings)).ToProperty();

Here is a really crude (the read method isn't very robust) example using a converter as well:

public class PropertyInfoConverter : JsonConverter
{
public override bool CanWrite
{
    get
    {
        return false;
    }
}

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

public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
{
    string propertyName = null;
    string assemblyName = null;
    string typeName = null;

    while (reader.Read())
    {
        if (reader.TokenType == JsonToken.PropertyName)
        {
            string value = reader.Value.ToString();

            switch (reader.Value.ToString())
            {
                case "Name":
                    if (reader.Read())
                    {
                        propertyName = reader.Value.ToString();
                    }
                    break;
                case "AssemblyName":
                    if (reader.Read())
                    {
                        assemblyName = reader.Value.ToString();
                    }
                    break;
                case "ClassName":
                    if (reader.Read())
                    {
                        typeName = reader.Value.ToString();
                    }
                    break;
            }
        }       
    }

    return Type.GetType(typeName + ", " + assemblyName).GetProperty(propertyName);
}

/// <inheritdoc />
public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
{
    // When the property "CanWrite" returns false this method is never expected to be called.
    throw new NotImplementedException();
}

}

Note, in order to force the deserialize method to use the custom converter you should call the generic version of it like this:

var deserialized = JsonConvert.DeserializeObject<PropertyInfo>(serialized, jsonSerializerSettings);

The same is true in your example which is why you weren't hitting your break point.