ASP.NET MVC dropdownlist级联错误无法将属性“值”设置为null

Question

Hy.
I want to make dropdownlist cascadin. select dropdownlist and send editorfor.but
Cannot set property 'value' of null error . I would like to send a value to editorfor a value of dropdownlist.
Can you help me?

   public JsonResult GetPrice(string log)
        {
            int id = 1;
            HomeController.sqlconnection con = new HomeController.sqlconnection();
            string FIRMA = "select t.FIRMA,t.donem FROM dbo.TBLFRM as t where t.ID=" + id + "";
            SqlCommand cmd = new SqlCommand(FIRMA, con.connect());
            SqlDataReader rdrr = cmd.ExecuteReader();
            rdrr.Read();
            string firma = rdrr["FIRMA"].ToString();
            string donem = rdrr["DONEM"].ToString();
            ExtreModel item = new ExtreModel();
            item.ItemList = new List<ExtreModel>();
            string urun = "select P.PRICE from DBO.LG_" + firma + "_PRCLIST as p,DBO.LG_" + firma + "_ITEMS as I WHERE P.CARDREF=I.LOGICALREF AND P.CARDREF=" + log + "";

            SqlCommand cmdd = new SqlCommand(urun, con.connect());            
                SqlDataReader rdr = cmdd.ExecuteReader();
            rdr.Read();
                   string PRICE = rdr[0].ToString();
                con.connect().Close();
                return Json(PRICE, JsonRequestBehavior.AllowGet);

        }



 <script>
        $("#LOGI").change(function () {
            var select = $(this);
            var cityname = select.val();
            if (cityname != "") {
                $.ajax({
                    method: "GET",
                    url: '/Mobil/GetPrice' + '?log=' + cityname,
                    beforeSend: function () {

                    }
                }).done(function (result) {
                    document.getElementById("fyt").value = result.PRICE;
                });
            } else {
            }
        });
    </script>

Answer 1

The problem seems coming from this return statement:

return Json(PRICE, JsonRequestBehavior.AllowGet);

This statement returns plain string value which doesn't contain PRICE property, so result.PRICE contains null value and causing null property assignment error message. If you want to return the price value, simply use this inside done function:

document.getElementById("fyt").value = result;

or in jQuery version:

$('#fyt').val(result);

But if you still want to return PRICE property, specify it inside JSON data:

return Json(new { PRICE = PRICE }, JsonRequestBehavior.AllowGet);

And the AJAX callback should be look like this:

$("#LOGI").change(function () {
    var cityname = $(this).val();
    if (cityname != "") {
        $.ajax({
            type: "GET",
            url: '/Mobil/GetPrice',
            data: { log: cityname }
            }).done(function (result) {
                $("#fyt").val(result.PRICE); // now the price property should exist
            });
    } else {
       // do something else
    }
});