将JSON数据作为KeyValue对发布到Rest Service

Question

我有Rest Service API，合同是

        [OperationContract]
        [WebInvoke(
                    Method = "POST",
                    RequestFormat = WebMessageFormat.Json,
                    ResponseFormat = WebMessageFormat.Json,
                    UriTemplate = "/CreateCustomActivity?token={authToken}"
                   )]
        ProcessStatus CreateCustomActivity(string authToken, ProspectActivityCompound activity);

ProspectActivityCompound ，dataobject，具有数据类型的 ActivityFields 属性

Dictionary<string,string>

这是我的requestData

{
    "RelatedProspectId": "2cd12345-1130-11e6-be13-06c7eb5c1234",
    "ActivityEvent": 156,
    "ActivityNote": "asdasdasd",
    "ActivityDate": "/Date(1468394160000)/",
    "ActivityDateTime": "2016-07-13 19:16:00",
    "Score": 9,
    "ActivityFields": {
        "Custom_1": "1234",
        "Custom_2": "asdf",
        "Custom_3": "dfg",
        "Custom_4": "qwe",
    }
}

我知道我可以用它来获取字典中的数据。

"ActivityFields": [
          {"Key":"Custom_1", "Value":"1234"},
          {"Key":"Custom_2", "Value":"fgh"},
          {"Key":"Custom_3", "Value":"wer"},
          {"Key":"Custom_4", "Value":"sdfs"}
        ]

我希望 ActivityFields 作为键值对，但现在它将变为null。 JSON格式应该是相同的，所以任何人都可以给我一个方法来接收这个JSON作为键值对。