ASP.NET MVC $.post call returning string…need help with format for jqGrid

If you try to solve the problem for jqGrid only you can choose another way.

You can use dataUrl and buildSelect properties of editoptions or searchoptions instead of value property. This features are introduced specially for the usage in AJAX. The dataUrl defines url provided results in the form like

<select><option value="1">One</option> <option value="2">Two</option></select>

If for you is easer to return JSON results from the server your custom function buildSelect will help. As the parameter it receive the data send from the server and it should return the string <select><option>...</option></select>. In the way you will achieve better results.

If you do decide to stay at your old way you should at least fix your code to following

foreach (var q in query)
{
     if (sb.Length != 0)
         sb.Append(';');
     sb.Append(q.Destination); // instead of sb.Append("ID");
     sb.Append(':');
     sb.Append(q.Destination);
}

to has "FedEx:FedEx;InTime:InTime;TNT:TNT" instead of "ID:FedEx; ID:InTime; ID:TNT; ".

UPDATED: You asked for a small example. Let us you can for example get all different values of the destinations strings as a List<string> and the name of this Method is GetAllDestinations. Then your action used by dataUrl can look like

public JsonResult GetDestinationList() {
    List<string> allDestinations = GetAllDestinations();
    Json(allDestinations, JsonRequestBehavior.AllowGet);
}

To use this action inside of editoptions or searchoptions of jqGrid you can define about following

{ name: 'destinations', ditable: true, edittype:'select',
  editoptions: { dataUrl:'<%= Url.Action("GetDestinationList","Home") %>',
                 buildSelect: function(data) {
                     var response = jQuery.parseJSON(data.responseText);
                     var s="<select>";
                     if (response && response.length) {
                         for (var i = 0, l=response.length; i<l ; i++) {
                             var ri = response[i];
                             s += '<option value="'+ri+'">'+ri+'</option>';
                         }
                     }
                     return s + "</select>";
                 }
                }
}

If you don’t want have actions which be used per HTTP GET you can use Json(allDestinations); instead of Json(allDestinations, JsonRequestBehavior.AllowGet); in the GetDestinationList action, but add to the list of jqGrid options an additional option

ajaxSelectOptions: { type: "POST" }

UPDATED 2: The answer is already old. In the interim the code of jqGrid where buildSelect will be called was changed. Now the buildSelect will be used inside of success handler of jQuery.ajax (see here) instead of the complete handler before (see the post and the post for example). So in the current version of jqGrid the line

var response = jQuery.parseJSON(data.responseText);

is not needed. The data is typically the parsed JSON data and so the lines

                 buildSelect: function(data) {
                     var response = jQuery.parseJSON(data.responseText);

in the code above can be replaced to

                 buildSelect: function(response) {