Problems with Json Serialize Dictionary<Enum, Int32>

Question

Hi,
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 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, Strings might be more expressive and easier to work with.

Answer 2

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 3

There seems to be no Solution other than using Dictionary<String, Int32> so there is no point in keeping the Question open.