how to access ViewBag together with Json - asp.net-mvc

Question

I am implementing autocomplete functionality by returning database values with the help of Json and Linq.I need to implement edit functionality. For edit functionality I need to return viewBag data to my view. But I couldn't access my viewBag while returning Json result.
public JsonResult Index(string Prefix,int id = 0)
{
SqlConnection sqcon2 = new SqlConnection(conn);
SqlCommand cmd2 = new SqlCommand();
SqlDataAdapter sd2 = new SqlDataAdapter(cmd2);
DataTable dt2 = new DataTable();
cmd2.Connection = sqcon2;
cmd2.CommandText = "sps_userLocationByID";
cmd2.CommandType = System.Data.CommandType.StoredProcedure;
cmd2.Parameters.AddWithValue("#id", id);
sqcon2.Open();
sd2.Fill(dt2);
sqcon2.Close();
foreach (DataRow dr2 in dt2.Rows)
{
ViewBag.cityName = dr2["CityName"].ToString();
ViewBag.Name = dr2["Name"].ToString();
}
SqlConnection sqcon = new SqlConnection(conn);
SqlCommand cmd = new SqlCommand();
SqlDataAdapter sd = new SqlDataAdapter(cmd);
DataTable dt = new DataTable();
cmd.Connection = sqcon;
cmd.CommandText = "sps_userCity";
cmd.CommandType = System.Data.CommandType.StoredProcedure;
sqcon.Open();
sd.Fill(dt);
sqcon.Close();
List<CityModel> ObjList = new List<CityModel>();
foreach (DataRow dr in dt.Rows)
{
CityModel st = new CityModel();
st.CityName = dr["CityName"].ToString();
ObjList.Add(st);
}
var CityName = (from N in ObjList
where
N.CityName.ToLower().StartsWith(Prefix.ToLower())
select new { N.CityName });
return Json(CityName, JsonRequestBehavior.AllowGet);
}

Answer 1

you can use viewbag if you call another Actionresult method via Ajax.

Answer 2

ViewBag only exists in the context of a Razor view, which itself only exists if you're returning View(), PartialView(), etc. If you're returning JSON, that's all you get. You cannot utilize ViewBag.
That said, I think you're confused in general about how things work though. Initially your app is responding with an HTML document. Everything else, your action, view, etc. is all about getting to this HTML document that can finally be returned to the client, a web browser in this case.
Once that response has been sent. The server is done. Client-side, the web browser parses the document and creates various object models: the DOM, CSSOM, etc. It then uses these object models to render the page (the paint). During and after this process, your JavaScript is run. All of this is happening client-side, and the server doesn't know or care; it's already done its job.
Then, you're wanting some new information from the server. That requires a new request from the client, which will result in a new response from the server. That request could come in the form of navigation by the user within the browser (in which case the whole browser window/tab view will change) or in the form of an AJAX request, which leaves the current view in the browser window/tab as-is.
XMLHttpRequest, the actual JavaScript client class responsible for making AJAX requests, is what's referred to as a "thin client". It makes requests and receives responses, but it does not do anything with said response, in ontrast to a "thick client" like a web browser, which takes the response and does all the object model creation and rendering. Instead, a callback function is merely invoked. It is your responsibility to do something in that callback with the response you receive (update the DOM, etc.)
All this is to say that doing anything with ViewBag while returning a JSON response to an AJAX request makes absolutely zero sense, because the view is not changing. You seem to be imagining that change ViewBag would somehow automatically update something on the page that was previously added via ViewBag in your initial Razor view. That's not the case, and it's not how things work. If you want to alter something on the page, the new value needs to be returning as part of the JSON response from your AJAX request, and then you must use that new value to alter the DOM accordingly.