CODEWITHSUNDEEP
c#json.netabstract-classjson-deserialization
Sun
Sun

Reputation: 4708

JsonConvert deserialize an array of abstract classes

Let's say I have the following class structure (Building is an abstract class):

public class Street
{
    public string StreetName { get; set; }

    public Building[] Buildings { get; set; }
}

public abstract class Building
{
    public string Name { get; set; }
}

public class House : Building
{
    public int Floors { get; set; }
}

public class Flat : Building
{
    public int WhichFloor { get; set; }
}

I then create a street object with a few flats in the buildings array:

Flat f1 = new Flat { Name = "Flat 1", WhichFloor = 1 };
Flat f2 = new Flat { Name = "Flat 2", WhichFloor = 2 };

Street street = new Street
{
    StreetName = "Street Name",
    Buildings = new[] { f1, f2 }
};

Using JsonConvert I then Serialize the object:

var toJson = JsonConvert.SerializeObject(street);

Now I want to convert the json back to a street object:

var fromJson = JsonConvert.DeserializeObject<Street>(toJson);

This fails with the following error:

"Could not create an instance of type Building. Type is an interface or abstract class and cannot be instantiated. Path 'Buildings[0].WhichFloor'"

How can I tell the JsonConvert class that Buildings should be an array of flats?

Upvotes: 3

Views: 7034

Answers (2)

Amir Touitou
Amir Touitou

Reputation: 3441

public abstract class JsonCreationConverter<T> : JsonConverter
{
    protected abstract T Create(Type objectType, JObject jObject);

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

    public override object ReadJson(JsonReader reader,Type objectType,
        object existingValue, JsonSerializer serializer)
    {
        try
        {
            var jObject = JObject.Load(reader);
            var target = Create(objectType, jObject);
            serializer.Populate(jObject.CreateReader(), target);
            return target;
        }
        catch (JsonReaderException)
        {
            return null;
        }
    }

    public override void WriteJson(JsonWriter writer, object value,
        JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

Now implement this interface

public class SportActivityConverter : JsonCreationConverter<BaseSportActivity>
{
    protected override BaseSportActivity Create(Type objectType, JObject jObject)
    {
        BaseSportActivity result = null;
        try
        {
            switch ((ESportActivityType)jObject["activityType"].Value<int>())
            {
                case ESportActivityType.Football:
                    result = jObject.ToObject<FootballActivity>();
                    break;

                case ESportActivityType.Basketball:
                    result = jObject.ToObject<BasketballActivity>();
                    break;
            }
            
        }
        catch(Exception ex)
        {
            Debug.WriteLine(ex);
        }

        return result;
        
    }
}

Upvotes: 0

FaizanHussainRabbani
FaizanHussainRabbani

Reputation: 3439

As per @Evk's shared link, you should try setting TypeNameHandling to TypeNameHandling.Auto while serializing and deserializing:

var toJson = JsonConvert.SerializeObject(street, Newtonsoft.Json.Formatting.Indented, new JsonSerializerSettings
{
    TypeNameHandling = TypeNameHandling.Auto
});


var fromJson = JsonConvert.DeserializeObject<Street>(toJson, new JsonSerializerSettings
{
    TypeNameHandling = TypeNameHandling.Auto
});

Upvotes: 11

Related Questions