The parameters dictionary contains a null entry for parameter id - asp.net-mvc-4

Question

function GetStatevalue() {
var state_id= $("#ddlstate").val();
var city = $("#txtcity").val();
var datao = new Object();
datao={ state:state_id ,city_name: city }
var url = "/city/AddCity";
$.ajax({
url: url,
data:datao ,
cache: false,
type: "POST",
dataType: "json",
success: function (datao) {
},
error: function (reponse) {
alert("error : " + state_id);
}
});
Html Form
#Html.DropDownListFor(model => model.tbl_state.coutry_id, (SelectList)ViewBag.country_nm, "Select Country", new {#id="coutry_id" , #onchange="GetState(this.value)"})
<select id="ddlstate" name="ddlstate" style="width: 200px" >
#Html.TextBoxFor(model =>model.tbl_city.city_name ,new {#id="txtcity" })
<input type="submit" id="save" value="Add" name="actiong" onclick="GetStatevalue();" />
Controller
[HttpPost]
public ActionResult AddCity(int id,String city_name)
{
tbl_city data = new tbl_city();
data.city_name = city_name;
data.state_id = id;
db.tbl_city.Add(data);
db.SaveChanges();
return Json(data);
}
The parameters dictionary contains a null entry for parameter 'id' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult AddCity(Int32, System.String)' in 'test_app.Controllers.cityController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

Answer 1

After seeing your JqueryCode , you actionresult method should look like:
[HttpPost]
public ActionResult AddCity(int state,String city_name)
//bcoz{ state(action variablename):state_id ,city_name(action variablename): city }
{
tbl_city data = new tbl_city();
data.city_name = city_name;
data.state_id = id;
db.tbl_city.Add(data);
db.SaveChanges();
return Json(data);
}