将数据从jquery发布到控制器时出错

Question

当我尝试将ContentType放入按钮点击事件的ajax调用时，我收到错误

viewmodel = ko.observableArray();
$(document).ready(function () {
    $.ajax({
        url: "/Render/LoadSurveyQuestions?sg=" + getUrlVars()["g"] + "&stg=" + getUrlVars()["sig"],
        success: function (result) {
            viewmodel = ko.mapping.fromJS(result);
            ko.applyBindings(viewmodel, document.getElementById("tblQuestions"));
        }
    });
    $("#btnNext").click(function () {
        $.ajax({
            type: 'post',
            data: ko.toJSON(viewmodel),
            url: "/Render/SaveSurveyQuestionOptions",
            //contentType: "application/json; charset=utf-8",
            //   dataType: "json", 
            success: function (result) {}
        });
    });

我正在使用以下控制器方法 为了保存list.i我收到错误 使用ajax调用此方法时。

[System.Web.Http.HttpPost]
    [JsonFilter(Param = "listobj", JsonDataType = typeof (List < SurveyQuestion > ))]
    public void SaveSurveyQuestionOptions(List < SurveyQuestion > listobj) {

        if (listobj.Count > 0) {
            foreach(SurveyQuestion objSurveyQuestion in listobj) {
                foreach(SurveyOption objOption in objSurveyQuestion.OptionList) {
                    //if (objOption.OptionSelected)
                    //{
                    //    objSurveyQuestion.OptionId = objOption.OptionID;
                    //    objSurveyQuestion.OptionText = objOption.OptionText;
                    //}
                }
                //osurveymanager.InsertQuestionAnswers(objSurveyQuestion);

            }

        }
    }