Question

I am trying to serialize a .net object contains another data contract object as a parameter. The code is as follows…

[DataContract]
        public class JsonObject2
        {
            [DataMember(Name = "field1")]
            string field1 { get; set; }
            [DataMember(Name = "field2")]
            string field2 { get; set; }
            [DataMember(Name = "field3")]
            object[][] test = { new object[]{"key1", "value1"}, new object[]{"key2", "value2"}, new object[]{"key3", "value3"} };
        }

        [DataContract]
        public class JsonObject3
        {
            [DataMember(Name = "field1")]
            public string field1 { get; set; }
            [DataMember(Name = "field2")]
            public object field2 { get; set; }
        }

DataContractJsonSerializer dcjs2 = new DataContractJsonSerializer(typeof(JsonObject3));

                JsonObject3 obj3 = new JsonObject3();
                obj3.field1 = "hello";
                obj3.field2 = new JsonObject2();
                dcjs2.WriteObject(s, obj3);
                s.Position = 0;
                MessageBox.Show(new StreamReader(s).ReadToEnd());

Doing the above, results in the following exception…

“{“Type ‘JSONParser.Form1+JsonObject2’ with data contract name ‘Form1.JsonObject2:http://schemas.datacontract.org/2004/07/JSONParser’ is not expected. Add any types not known statically to the list of known types – for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer.”}”

I can’t figure out how to carry out any of the recommendations given in that exception.

1. How do you add to the list of KnownTypes ?
2. How do you use the KnownTypeAttribute ?

Answer 1

Ok, figured out how to do it. I didn’t want to delete this question in case someone else finds it useful, so here is the solution…

[DataContract]
    [KnownType(typeof(JsonObject2))]
    public class JsonObject2
    {
        [DataMember(Name = "field1")]
        string field1 { get; set; }
        [DataMember(Name = "field2")]
        string field2 { get; set; }
        [DataMember(Name = "field3")]
        object[][] test = { new object[]{"key1", "value1"}, new object[]{"key2", "value2"}, new object[]{"key3", "value3"} };
    }

    [DataContract]
    public class JsonObject3
    {
        [DataMember(Name = "field1")]
        public string field1 { get; set; }    
        [DataMember(Name = "field2")]
        public object field2 { get; set; }
    }

Notice the [KnownType(typeof(JsonObject2))] above the declaration of the JsonObject2 class ? That solved it.