Deserialize specific enum into system.enum in Json.Net

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The difficulty here is that System.Enum is an abstract class, so it is impossible to deserialize a value of unknown concrete type as such a type. Rather, one needs to have the specific type information in the JSON somewhere, however Json.NET will serialize an enum as a string or an integer (depending upon whether a StringEnumConverter is applied) — but not an as an object, thus leaving no opportunity for a polymorphic "$type" property to be added.

The solution is, when serializing, to serialize a generic wrapper class that can convey the concrete type information:

public abstract class TypeWrapper
{
    protected TypeWrapper() { }

    [JsonIgnore]
    public abstract object ObjectValue { get; }

    public static TypeWrapper CreateWrapper<T>(T value)
    {
        if (value == null)
            return new TypeWrapper<T>();
        var type = value.GetType();
        if (type == typeof(T))
            return new TypeWrapper<T>(value);
        // Return actual type of subclass
        return (TypeWrapper)Activator.CreateInstance(typeof(TypeWrapper<>).MakeGenericType(type), value);
    }
}

public sealed class TypeWrapper<T> : TypeWrapper
{
    public TypeWrapper() : base() { }

    public TypeWrapper(T value)
        : base()
    {
        this.Value = value;
    }

    public override object ObjectValue { get { return Value; } }

    public T Value { get; set; }
}

Then use serialize the wrapper when serializing your class:

    /// <summary>
    /// The enum flag associated with the rule, if applicable.  CAN be null.
    /// </summary>
    [JsonIgnore]
    public System.Enum RuleFlagEnum { get; set; }

    [JsonProperty("RuleFlagEnum", TypeNameHandling = TypeNameHandling.All)]
    TypeWrapper RuleFlagEnumValue
    {
        get
        {
            return RuleFlagEnum == null ? null : TypeWrapper.CreateWrapper(RuleFlagEnum);
        }
        set
        {
            if (value == null || value.ObjectValue == null)
                RuleFlagEnum = null;
            else
                RuleFlagEnum = (Enum)value.ObjectValue;
        }
    }

This produces JSON like the following:

{
  "RuleType": "ModifyDifficulty",
  "RuleFlagEnum": {
    "$type": "Question31351262.TypeWrapper`1[[Question31351262.MyEnum, MyApp]], MyApp",
    "Value": "Two, Three"
  },
}

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