Question

I’m trying to use the official jQuery autocomplete plugin with an ASMX web service in an ASP.NET 3.5 Web Forms application. If I understand it correctly, the autocomplete plugin can only use HTTP GET to call a service (with two query string parameters: q and limit). I figured out how to make the web service respond to the HTTP GET calls, but I cannot figure out how to make it return JSON data (even though the service returns JSON data when I call it using jQuery $.ajax with type=’POST’, when called from the autocomplete plugin it always returns XML). Here are some code snippets:

Web service:

[ScriptService]
[WebService(Namespace = "http://tempuri.org/")]
public class UserWS: WebService
{
  [WebMethod]
  [ScriptMethod(UseHttpGet=true, ResponseFormat=ResponseFormat.Json)]
  public List<UserDisplayInfo> GetUsers
  (
    string q,
    int limit
  )
  {
    List<UserDisplayInfo>users = GetUsers(q, limit);
    return users.ToList();
  }
}

Web page:

$("#test").autocomplete(
  "./Services/UserWS.asmx/GetUsers",
  {
    dataType: 'json',
    type: 'POST', // this setting is ignored
    contentType: 'application/json;charset=utf-8',
    parse: function(data) 
    {
      //...
    }
});

If this is not possible I wonder what would be a better alternative:

• fixing autocomplete plugin to use HTTP POST and JSON data instead of GET and query string parameters;
• using a different autocomplete plugin (I looked at a few, but at this point the official plugin has most recommendations, and I’m not sure if other plugins support HTTP POST);
• an alternative to ASMX web service, such as WCF web service (I would not want to use WCF because ASMX web service is simpler to implement — no web.config changes, no contracts, no interfaces — and it gives me everything I need);
• something else.

I found several similar questions at StackOverflow, but I did not find the answer that would work for me. Any (good) ideas?

Answer 1

Autocomplete plugin wants results in plain text format, not JSON. Each item should be on a separate line:

foo\n
bar\n
baz\n

Try replacing web service with generic handler (.ashx):

public class MyHandler : IHttpHandler
{

  public void ProcessRequest(HttpContext context)
  {
    context.Response.ContentType = "text/plain";
    context.Response.Write("foo\nbar\nbaz");
  }

  public bool IsReusable
  {
    get { return false; }
  }
}

On the side note you can’t use GET if you want ASMX web service to return JSON. See How to let an ASMX file output JSON.