JSONP Callback, response data is null

问题

Following on from my original question: Not receiving JSONP callback

I am now trying to process the information in the JSONP callback and I cannot seem to get any data to "load" i.e. the rsp object appears to be empty/null.

VenuOffersDAO (UPDATE: Not using this to simplify things)

This is in a separate class library project outside of the MVC4 project. So, my controller does not use a model.

public static List<Offer> GetVenuesOffers(int venueId)
{
    using (var ctx = new MyDbEntities())
    {
        var venue = (...removed for brevity...).FirstOrDefault();

        return 
            venue != null 
            ? GetVenuesOffers(venue) 
            : null;
    }
}

public static List<Offer> GetVenuesOffers(Venue venue)
{
    using (var ctx = new MyDbEntities())
    {
        ...removed for brevity...
        return offers.ToList();
    }
}

Controller (UPDATE: Now using a more simple object instead of the generated EF one.)

This is within a ASP.NET MVC4 project.

public class VenueOffersController : Controller
{
    [JsonpFilter]
    public JsonResult GetOffersForVenue(int venueId)
    {
        var offers = new List<VenueOffers>();

        using (var ctx = new BoonEntities())
        {
            offers = (from o in ctx.Offers
                      where o.VenueID == venueId
                      select new VenueOffers
                          {
                              Id = o.ID,
                              VenueId = venueId,
                              Title = o.Title
                          }).ToList();
        }

        return Json(offers.ToList(), JsonRequestBehavior.AllowGet);
    }
}

[Serializable]
public class VenueOffers
{
    public int Id { get; set; }
    public int VenueId { get; set; }
    public string Title { get; set; }
}

HTML Page

This is within a ASP.NET v4 Web-Forms Project as a plain HTML file.

<head>
    <title></title>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
</head>
<body>
    <script type="text/javascript">
        var url = "http://localhost/MySite.ContentDelivery/VenueOffers/GetOffersForVenue/?";

        function getOffers() {
            // build the URL
            debugger;
            var call = url + "venueId=48&callback=?";

            // make the ajax call
            $.getJSON(call, function (rsp) {
                alert(rsp.offers);     //  'undefined'
                alert(rsp);            //  empty
                var html = "";
                $.each(rsp.offers.offer, function () {
                    var offer = this;
                    html += "<span" + offer.Title + "</span> <br />";
                });

                $("#offersDiv").append(html);
            });
        }

        // get the offers
        $(document).ready(function () {
            alert('go..');
            $(getOffers);
        });
    </script>
    <div id="offersDiv"></div>
</body>

回答1:

Your controller action is returning an array (List<Offer>). Your JSON result probably looks something like this:

[{"Name":"some name 1"}, {"Name":"some name 2"}, ...]

So inside your success callback you could loop through the results:

$.getJSON(call, function (rsp) {
    var html = "";
    $.each(rsp, function () {
        var offer = this;
        html += "<span>" + offer.Name + "</span><br />";
    });
    $("#offersDiv").append(html);
});

Also put a breakpoint inside your controller action and make sure that the offers variable that you are returning actually contains some elements.

Also notice that you had a missing closing > for the span element you were generating dynamically.

Another problem I can see with your code is that you could replace your document.ready handler with:

$(getOffers);

来源：https://stackoverflow.com/questions/15054200/jsonp-callback-response-data-is-null

标签

ASP.NET

jquery

asp.net-mvc-4

jsonp