Making a call to a page that returns JSON using ASP.net AJAX

Question

I have a Page that expects a POST Request and returns some JSON. Essentially it's an .ashx Page, but that doesn't really matter.

When using jQuery, I would use jQuery.Post with "json" as dataType to simply make the POST request and get an object back. However, for the current project I mainly use ASP.net AJAX and I don't want to add jQuery just for the call.

For ASP.net AJAX, I only found information on how to call a "traditional" web service though, which means adding a asp:ServiceReference to the ScriptManager and having a "real" Web Service at the end.

Is there a simpler way to make a POST call to a Page? I could live with getting the raw JSON and then manually eval()ing it, but I don't want to create a full asmx web service (deploying them on SharePoint is a bit painful, and my ashx handler works fine)

Answer 1

Sys.Net.WebServiceProxy.invoke(url, methodName, useGet, parametersDictionary, onSuccess, onFailure, userContext, timeout);

All params optional except the first.

parametersDictionary is like { foo: bar } -- the parameters will be sent as JSON in the body if you are posting, or as parameters on the query string if it is GET (each parameter separately json serialized -- which btw means strings look like "foo", with the quotes).

onSuccess if a callback that takes the data as the first parameter (already deserialized object).

onFailure gets an error object as the first parameter which contains a get_message() method to get the error message, and some other things.

Answer 2

You can use the invoke method of the Sys.Net.WebServiceProxy class directly.

The method signature looks like this:

invoke(path, methodName, useHttpGet, parameters, succeededCallback, failedCallback, userContext, timeout);

Assuming that your service actually returns JSON, then the first argument to succeededCallback should be a JSON object.

Answer 3

Sys.Net.WebServiceProxy wasn't helpful because it seems to expect a real web service at the end - Request.Form was empty on the server side, parametersDictionary seems to be ignored. There also seems to be no override to wire up another executor instead.

I now solved it by manually creating a Sys.Net.WebRequest. I'l going to take a look at the jQuery sources as this approach is a lot more complex/"bare-metal", but as said, I don't want to add a dependency on jQuery if it isn't needed.

var ApplicationFunctions = {
    showDialog: function(someParam, someOtherParam) {
        var sb = new Sys.StringBuilder("Do you really want to do '");
        sb.append(someParam);
        sb.append("' ?");
        var msg = sb.toString();
        if (confirm(msg)) {
            var myWebRequest = new Sys.Net.WebRequest();
            myWebRequest.set_url('SomeService.ashx');
            myWebRequest.set_httpVerb('POST');
            // Manually build POST body. This would need escaping/urlencoding
            // I think if I couldn't guarantee that the parameters are 'clean'
            var bodySb = new Sys.StringBuilder("postParam=");
            bodySb.append(someParam);
            bodySb.append("&anotherPostParam=");
            bodySb.append(someOtherParam);
            var body = bodySb.toString();
            myWebRequest.set_body(body);
            myWebRequest.get_headers()["Content-Length"] = body.length;
            // also check out usercontext to pass additional data into the completed function
            // http://msdn.microsoft.com/en-us/library/bb397436.aspx
            myWebRequest.add_completed(ApplicationFunctions.onCallCompleted);
            myWebRequest.set_timeout(10 * 1000); // 10 seconds
            myWebRequest.invoke();
        }
    },
    onCallCompleted: function(response) {
        if (response.get_timedOut()) {
            alert("Timed Out!");
            return;
        }
        if (response.get_statusCode() !== 200) {
            alert("Status Code not OK");
            return;
        }
        if (!response.get_responseAvailable()) {
            alert("No data available?!");
            return;
        }
        // Better use a JSON parser
        // http://www.json.org/js.html
        var responseData = eval('(' + response.get_responseData() + ')');
        alert("Success: " + responseData.SomeField);
    }
}