Problems with Json Serialize Dictionary<Enum, Int32>

Question

whenever i try to serialize the dictionary i get the exception:

System.ArgumentException: Type 
'System.Collections.Generic.Dictionary`2[[Foo.DictionarySerializationTest+TestEnum, Foo, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null],[System.Int32, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]'
is not supported for serialization/deserialization of a dictionary,
keys must be strings or object

My Testcase is:

public class DictionarySerializationTest
{
  public enum TestEnum { A, B, C }
  //tried with numbers, too: public enum TestEnum { A = 1, B = 2, C = 3 }

  public void SerializationTest()
  {
    Dictionary<TestEnum, Int32> data = new Dictionary<TestEnum, Int32>();

    data.Add(TestEnum.A, 1);
    data.Add(TestEnum.B, 2);
    data.Add(TestEnum.C, 3);

    JavaScriptSerializer serializer = new JavaScriptSerializer();
    String result = serializer.Serialize(data);
    // Throws
  }

  public void SerializationToObjectTest()
  {
    Dictionary<object, Int32> data = new Dictionary<object, Int32>();

    data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.A), 1);
    data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.B), 2);
    data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.C), 3);

    JavaScriptSerializer serializer = new JavaScriptSerializer();
    String result = serializer.Serialize(data);
    // Throws
  }

  public void SerializationStringTest()
  {
    Dictionary<String, Int32> data = new Dictionary<String, Int32>();

    data.Add(TestEnum.A.ToString(), 1);
    data.Add(TestEnum.B.ToString(), 2);
    data.Add(TestEnum.C.ToString(), 3);

    JavaScriptSerializer serializer = new JavaScriptSerializer();
    String result = serializer.Serialize(data);
    // Succeeds
  }

}

Of course i could use .ToString() whenever i enter something into the Dictionary but since it's used quite often in performance relevant methods i would prefer using the enum.

My only solution is using .ToString() and converting before entering the performance critical regions but that is clumsy and i would have to change my code structure just to be able to serialize the data.

Does anyone have an idea how i could serialize the dictionary as <Enum, Int32> ?

I use the System.Web.Script.Serialization.JavaScriptSerializer for serialization.

UPDATE:

I switched to Dictionary<String, Int32> now and it works but i hope someone shows a solution as i don't really like using strings in place of a type safe enum.

Answer 1

I know it's late, but maybe someone else can make use of it in the future. You can achieve what you need using LINQ:

Dictionary<TestEnum, Int32> data = new Dictionary<TestEnum, Int32>();

data.Add(TestEnum.A, 1);
data.Add(TestEnum.B, 2);
data.Add(TestEnum.C, 3);

JavaScriptSerializer serializer = new JavaScriptSerializer();
Dictionary<string, Int32> dataToSerialize = data.Keys.ToDictionary(p => p.ToString(), p => data[p]);
string dataSerialized = serializer.Serialize(dataToSerialize);

Answer 2

Use Newtonsoft (Newtonsoft.Json.dll) to serialize the Dictionary object and you'd be fine. It's a popular third party library you would have to download and include in your project as a reference.

See example below:

var _validationInfos = new Dictionary<ImportField, ValidationInfo>();
var serializedData = JsonConvert.SerializeObject(_validationInfos);

Answer 3

I think that you are having trouble because TestEnum is declared as a private enum . Try marking it as a public enum . The serializer needs to be able to find your enum via reflection in order to serialize it.

Also according to the Docs , the enums must have integer values. So you might want to write:

public enum TestEnum { A = 1, B = 2, C =3 }

Also, the docs say that this enum will just get mapped to its corresponding integer value during the serialization. So depending on what you are doing on the other end, String s might be more expressive and easier to work with.

Answer 4

Exception says "keys must be strings or object" so try

data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.A));
data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.B));
data.Add(Enum.ToObject(typeof(TestEnum), TestEnum.C));

I did not test it though, just a guess.

Answer 5

I've created JavaScriptSerializer extension DeserializeDictionary- see http://geekswithblogs.net/mnf/archive/2011/06/03/javascriptserializer-extension-deserializedictionarytkey-tvalue.aspx

public static Dictionary<TKey, TValue>  DeserializeDictionary<TKey, TValue>(this JavaScriptSerializer jss, string jsonText)
{
    var dictWithStringKey = jss.Deserialize<Dictionary<string,TValue>>(jsonText);
    var dict=dictWithStringKey.ToDictionary(de => jss.ConvertToType<TKey>(de.Key),de => de.Value);
        return dict;
}