Can't cast objects from Dictionary after using json.net deserialization

Question

I have a problem with deserialized Dictionary. I can't cast objects from Dictionary to my type Remiza... I'm using Json.net and what I can see is that objects in Dictionary are JObject not Object and I can't cast them to my type. Here is my serialization/deserialization code:

    private static Dictionary<Type, List<Object>> _ekstensje = new Dictionary<Type, List<Object>>();

    public static void SerializeDictionary()
        {
            string json = JsonConvert.SerializeObject(_ekstensje);
            System.IO.StreamWriter file = new System.IO.StreamWriter(@"c:\tmp\dictionary.json");
            file.WriteLine(json);

            file.Close();
        }

        public static void DeserializeDictionary()
        {
            string json;
            System.IO.StreamReader file = new System.IO.StreamReader(@"c:\tmp\dictionary.json");
            json = file.ReadToEnd();

            file.Close();
            _ekstensje = JsonConvert.DeserializeObject<Dictionary<Type, List<Object>>>(json);//Deserializacja Dictionary
            Debug.WriteLine(_ekstensje);
        }

        public static List<Object> GetEkstensja(Type className)
        {
            List<Object> list = _ekstensje[className];
            return list;
        }

Exectution:

        ObjectPlus.DeserializeDictionary();
        List<Object> list = ObjectPlus.GetEkstensja(typeof(Remiza));
        foreach (Object o in list)
        {
            Remiza r = (Remiza) o;
            listaRemiz.Add(r);
        }

My problem is when casting to "Remiza" I have that exception:

An exception of type 'System.InvalidCastException' occurred in Osek_MAS_WPF.exe but was not handled in user code. Additional information: Unable to cast object of type 'Newtonsoft.Json.Linq.JObject' to type 'Osek_MAS_WPF.Remiza'.

Thanks for any help!

Answer 1

In order to successfully serialize and deserialize polymorphic types with Json.NET, you need to set TypeNameHandling = TypeNameHandling.Auto, like so:

public class ObjectPlus
{
    // Replace with whatever file name is appropriate.  My computer doesn't have a "c:\tmp" directory.
    static string JsonFileName { get { return Path.Combine(Path.GetTempPath(), "dictionary.json"); } }

    static JsonSerializerSettings JsonSettings { get { return new JsonSerializerSettings { TypeNameHandling = TypeNameHandling.Auto, Formatting = Formatting.Indented }; } }

    private static Dictionary<Type, List<Object>> _ekstensje = new Dictionary<Type, List<Object>>();

    public static void SerializeDictionary()
    {
        var path = JsonFileName;

        using (var stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.Read))
        using (var writer = new StreamWriter(stream))
        {
            var serializer = JsonSerializer.CreateDefault(JsonSettings);
            serializer.Serialize(writer, _ekstensje);
        }
    }

    public static void DeserializeDictionary()
    {
        var path = JsonFileName;
        try
        {
            using (var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read))
            using (var reader = new StreamReader(stream))
            using (var jsonReader = new JsonTextReader(reader))
            {
                var serializer = JsonSerializer.CreateDefault(JsonSettings);
                _ekstensje = serializer.Deserialize<Dictionary<Type, List<Object>>>(jsonReader);
            }
        }
        catch (FileNotFoundException)
        {
            // File was not created yet, dictionary should be empty.
            _ekstensje.Clear();
        }
    }

    public static List<Object> GetEkstensja(Type className)
    {
        List<Object> list = _ekstensje[className];
        return list;
    }

    public static void AddEkstensja<T>(T obj)
    {
        List<Object> list;
        if (!_ekstensje.TryGetValue(obj.GetType(), out list))
            list = _ekstensje[obj.GetType()] = new List<object>();
        list.Add(obj);
    }

    internal static string ShowJsonContents()
    {
        if (!File.Exists(JsonFileName))
            return string.Empty;
        return File.ReadAllText(JsonFileName);
    }
}

You should now be able to serialize and deserialize your dictionary when it contains an instance of Remiza.

This will work for types that serialize to objects or collections. However, if your dictionary contains types that serialize to JSON primitives -- for instance an enum or a long -- you may need to encapsulate them in a type wrapper along the lines of Deserialize specific enum into system.enum in Json.Net.

(Incidentally, your _ekstensje dictionary isn't thread-safe.)

Answer 2

This should allow you to convert the JObect to your Remiza type.

ObjectPlus.DeserializeDictionary();
    List<Object> list = ObjectPlus.GetEkstensja(typeof(Remiza));
    foreach (Object o in list)
    {
        Remiza r = o.ToObject<Remiza>();
        listaRemiz.Add(r);
    }

I got this from the stackoverflow answer at the link below. If what I put doesn't work take a look at the link and it should help you to get it running.

https://stackoverflow.com/a/10221594/634769