Is there any way to JSON.NET-serialize a subclass of List that also has extra properties?

Question

Ok, we\'re using Newtonsoft\'s JSON.NET product, which I really love. However, I have a simple class structure for hierarchical locations that look roughly like this...

Answer 1

Ok... so here's what I've come up with. I had to write my own JsonConverter. I basically use it to create an inline JObject that has the properties structured as I wanted them to persist, then I persist that. I then do the reverse when I read it back out.

However, the down'side is it doesn't use reflection or any other such things so this only works for this specific type which I had to hand-code property by property (in this case there are only two so that's good!) and it also doesn't take advantage of the DefaultValues processing which I have to re-emulate manually, meaning the attributes are basically ignored unless I reflect upon them. Still, this works. Perfect? No, but hey... things rarely are!

Of course, comments are welcome and encouraged!

public class LocationListJsonConverter : JsonConverter
{
    public override bool CanConvert(System.Type objectType)
    {
        return objectType == typeof(LocationList);
    }

    public override object ReadJson(JsonReader reader, System.Type objectType, object existingValue, JsonSerializer serializer)
    {
        var locationList = (existingValue as LocationList) ?? new LocationList();
        var jLocationList = JObject.ReadFrom(reader);

        locationList.IsExpanded = (bool)(jLocationList["IsExpanded"] ?? false);

        var jLocations = jLocationList["_Items"];
        if(jLocations != null)
        {
            foreach(var jLocation in jLocations)
            {
                var location = serializer.Deserialize<Location>(new JTokenReader(jLocation));
                locationList.Add(location);
            }
        }

        return locationList;

    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var locationList = value as LocationList;

        JObject jLocationList = new JObject();

        if(locationList.IsExpanded)
            jLocationList.Add("IsExpanded", true);

        if(locationList.Count > 0)
        {
            var jLocations = new JArray();

            foreach(var location in locationList)
            {
                jLocations.Add(JObject.FromObject(location, serializer));
            }

            jLocationList.Add("_Items", jLocations);

        }

        jLocationList.WriteTo(writer);

    }

}

Answer 2

I need a class named FieldGroup that also has some properties to group some Fields. I did that as this firstly.

public class FieldGroup : List<Field>{ ... }

It has the problem to serialize as the post said. So I modified the class as below. So I can handle with it the same as the class of *FieldGroup that derived from List<Field>.

public class FieldGroup : IPrintable, IEnumerable<Field>
{
    public PrintFormat GroupFormat { get; set; } = new PrintFormat();
    public List<Field> Fields { get; set; } = new List<Field>();

    public Field this[int index]
    {
        get => Fields[index];
        set => Fields[index] = value;
    }

    public void Add(Field field)
    {
        Fields.Add(field);
    }
    public IEnumerator<Field> GetEnumerator()
    {
        return new FieldEnumerator(Fields);
    }
    IEnumerator IEnumerable.GetEnumerator()
    {
        return GetEnumerator();
    }

    ...
}

Answer 3

Usually when I find myself fighting something like this it tells me I should consider another approach. In this case, I would recommend the following view model structure as an alternative:

public class Location
{
    public bool IsExpanded { get; set; }
    public string Name { get; set; }
    public List<Location> Locations { get; set; }
}

public class ViewModel
{
    public List<Location> RootLocations { get; set; }
}