Question

This one really has me stumped. I’m trying to deserialize the following JSON string which I get from a ASP.NET Web Service:

"{\"d\":{\"__type\":\"KPCServer.LogonResult\",\"User\":{\"UserId\":\"affaa328-5b53-430e-991a-22674ede6faf\",\"Email\":\"[e-mail]\",\"Alias\":\"Mike\",\"FullName\":\"Mike Christensen\",\"Password\":\"secret\",\"Location\":\"Redmond, WA\",\"ImageUrl\":null,\"DateOfBirth\":\"\\/Date(-62135568000000)\\/\",\"LastLogon\":\"\\/Date(1350450228000)\\/\",\"UserSince\":\"\\/Date(1197980020000)\\/\",\"MailingList\":true,\"Bio\":\"Test\"},\"NewUser\":false,\"Ticket\":\"FJEjfje87fjef88fe8FAF8fA88fAjk+AFJ9fja9Fa9Ff99aJF9aFjfA99fjaBFJ7zqmlcHn9Dfw=\"}}"

I have the following types:

public class User
{
   public Guid UserId { get; set; }
   public string Email { get; set; }
   public string Alias { get; set; }
   public string FullName { get; set; }
   public string Password { get; set; }
   public string Location { get; set; }
   public string ImageUrl { get; set; }
   public DateTime DateOfBirth { get; set; }
   public DateTime LastLogon { get; set; }
   public DateTime UserSince { get; set; }
   public bool MailingList { get; set; }
   public string Bio { get; set; }
}

[DataContract(Name="KPCServer.LogonResult")]
public class LogonResult
{
   [DataMember] public User User { get; set; }
   [DataMember] public bool NewUser { get; set; }
   [DataMember] public string Ticket { get; set; }
}

[DataContract]
[KnownType(typeof(LogonResult))]
public class Result<T>
{
   [DataMember]
   public T d { get; set; }
}

I then try to deserialize the string using:

using (MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(json)))
{
   DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(Result<T>));
   Result<T> result = serializer.ReadObject(stream) as Result<T>;

   return result.d;
}

Note: In the above method, T is of type LogonResult.

However, I get the following exception on ReadObject:

System.Runtime.Serialization.SerializationException was unhandled by user code
  HResult=-2146233076
  Message=JSON contains a '__type' member specifying the data contract name ':KPCServer.LogonResult'. The deserializer has no knowledge of any type that maps to this contract. Add the type corresponding to 'KPCServer.LogonResult' to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding it to the list of known types passed to DataContractSerializer. You can also often eliminate this error by avoiding the use of derived types where the JSON is produced.
  Source=System.ServiceModel.Web
  InnerException: 

If I run:

json = json.Replace("_type", "_blah");

Then everything works fine. This is using Silverlight on Windows Phone 8.

Answer 1

This is due to the fact that:

"\"__type\":\"KPCServer.LogonResult\""

doesn’t contain a data contract namespace. This is fixed by modifying the DataContractAttribute on LogonResult:

[DataContract(Name = "KPCServer.LogonResult", Namespace="")]
public class LogonResult
{
    [DataMember]
    public User User { get; set; }
    [DataMember]
    public bool NewUser { get; set; }
    [DataMember]
    public string Ticket { get; set; }
}