Question

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Ajax cross domain call

I have Asp.Net Controller methods which return JSON response. However I am unable to call it from a different domain using Jquery’s $.getJSON(...){}

Quick googling suggests that JSONP must be used. Question is what is the difference between JSON and JSONP? Is that just another new term? And if JSONP is working why I can’t I make JSON work? Is there any way to not use these fancy JSONP and use plain old JSON because I am afraid of any changes to my server side code.

Answer 1

You cannot make cross domain AJAX calls using JSON. You need to use JSONP. So instead of returning a regular JsonResult from your controller action write a custom action result that will wrap the JSON in a callback that is passed as parameter:

public class JsonpResult : ActionResult
{
    private readonly object _obj;

    public JsonpResult(object obj)
    {
        _obj = obj;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var serializer = new JavaScriptSerializer();
        var callbackname = context.HttpContext.Request["callback"];
        var jsonp = string.Format("{0}({1})", callbackname, serializer.Serialize(_obj));
        var response = context.HttpContext.Response;
        response.ContentType = "application/json";
        response.Write(jsonp);
    }
}

and then have your controller action return this custom action result:

public ActionResult SomeAction()
{
    var result = new[]
    {
        new { Id = 1, Name = "item 1" },
        new { Id = 2, Name = "item 2" },
        new { Id = 3, Name = "item 3" },
    };
    return new JsonpResult(balances);
}

Now you could consume this action cross domain:

var url = "http://example.com/SomeController/SomeAction/";
$.getJSON(url + '?callback=?', function (data) {
    alert(data);
});