Why does Json.NET serialization fail with [Serializable] and a lambda inside a read-only property?

Question

According to these release notes, Json.NET now supports the SerializableAttribute:

Json.NET now detects types that have the SerializableAttribute and

Answer 1

I installed and used JustDecompile and found that the compiler adds a field and a method to the class when the lambda is uncommented:

public class MyType
{
    [CompilerGenerated]
    private static Func<int, int> CS$<>9__CachedAnonymousMethodDelegate1;

    [CompilerGenerated]
    private static int <get_TotalWithLambda>b__0(int x) { ... }

    // ... plus the other class members ...
}

When the class has SerializableAttribute on it, Json.NET tries to serialize the private field, but can't since it's of type Func<int, int>. Removing the SerializableAttribute instructs Json.NET to ignore private fields and so it doesn't cause a problem.

Update: Json.NET 4.5 release 3 now makes this only a problem if you explicitly set IgnoreSerializableAttribute=false, or it can be resolved by adding the JsonObjectAttribute to the class..

Answer 2

I've changed IgnoreSerializableAttribute to true by default in release 3 which undoes the breaking change introduced in release 2 - http://json.codeplex.com/releases/view/85975

You can read more about it here - http://json.codeplex.com/discussions/351981