Return data from jQuery callback ASP.NET 2.0

Question

Hi

I am new to jQuery and I am implementing an example I found on CodeProjects.

What I need is to get a string with an imagename and new image index returned from the PageMethod I am calling. However each time I try to return something else than a number via Response.Write the callback fails and I go into the error function.

$(document).ready(function() {

var imageIndex = $("[id$='hdn_imageIndex']");
var app_path = $("[id$='hdn_app_path']");

$("#btn_next").click(function() {

    var json = "{'Index':'" + imageIndex.val() + "'}";
    var ajaxPage = app_path.val() + "/JSONProcessor.aspx?NextImage=1"; //this page is where data is to be retrieved and processed
    var options = {
        type: "POST",
        url: ajaxPage,
        data: json,
        contentType: "application/json;charset=UTF-8",
        dataType: "json",
        async: false,
        success: function(result) {

            alert("success: " + result.d);
            // I want my return value from my PageMethod HERE.
        },
        error: function(msg) { alert("failed: " + msg.d); }
    };

    var returnText = $.ajax(options).responseText;

});

});

The PageMethod in JSONProcessor.aspx looks like this:

public void NextImage()
{
    System.IO.StreamReader sr = new System.IO.StreamReader(Request.InputStream);
    string line = "";
    line = sr.ReadToEnd();
    JObject jo = JObject.Parse(line);

    int newImageIndex = -1;
    int oldImageIndex = int.Parse(Server.UrlDecode((string)jo["Index"]));
    List<string> images = (List<string>)Session["ShowHouseImages"];
    int noOfImages = images.Count;

    if (noOfImages > 0)
    {
        if (oldImageIndex == noOfImages - 1)
        {
            newImageIndex = 0;
        }
        else
        {
            newImageIndex = oldImageIndex + 1;
        }

        string[] result = ChangeImage(newImageIndex, images);

        Response.StatusCode = 200;
        Response.Write("1");
        // What I REALLY WANT TO RETURN IS THIS
        // Response.Write(string.Format("{0};{1};{2}", result[0], result[1], result[2]));
    }

    Response.Write("0");
}

JSON return from WebMethods does not seem to be a part of .NET 2.0. That is why I do it like this. Hope somebody can help me out.

Answer 1

To my understanding in the line

Response.Write(string.Format("{0};{1};{2}", result[0], result[1], result[2]));

you are not returning a correct JSON object. It should probably look something like

Response.Write(string.Format("{{images:[{0},{1},{2}]}}", result[0], result[1], result[2]));

This returns you an array with three elements. The produced output should be:

{images:[1,2,3]}

In JavaScript you can access data using result.images[0],result.images[1], etc. I'm not sure if you need to specify array object name (images).

I suggest you take a look at JSON website to get a better understanding of the syntax. This way you will be able to construct complex object by yourself.