请求的资源上不存在“ Access-Control-Allow-Origin”标头

Question

First of all I know that lot of questions have been asked about this, but I really tried to find out what's the problem, but nothing helped me. I'm working with C#, ASP.NET, Javascript, AJAX and trying to use an API to get some informations, but I get this error every time. When I tried with different API, works perfect. The API status is active, but response failed every time.

Error is looking like: 1

I added permissions in config file:

  <customHeaders>
    <add name="Access-Control-Allow-Origin" value="*" />
    <add name="Access-Control-Allow-Headers" value="Origin, X-Requested-With, Content-Type, Accept" />
    <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />
  </customHeaders>

but this didn't help me. What should I do now? I'm trying this for hours, and the same result.

Tried do add jsonp and crossDomain in ajax call, but this didn't help me too.

    $.ajax({
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },

        crossDomain : true,
        dataType: 'jsonp',
        url: url + id,
        type: 'GET',
        contentType: 'application/json;',
        success: function (valid) {
            if (valid) {
            } else {
            }
        }
    });
}

Thank you all for every answer.

Best regards

Answer 1

If you are using ASP.NET Web Api, try enabling cors in your http config.

        public static void Register(HttpConfiguration config)
    {            
        config.EnableCors();
        config.MapHttpAttributeRoutes() .......

i make ajax calls to such an API successfully like so..

            $.ajax({
            url: url,
            type: 'POST',
            dataType: 'json',
            contentType: 'application/json; charset=utf-8',

Answer 2

Also Remember to decorate your Api controller with EnableCors Attribute

[EnableCors(origins: "*", headers: "*", methods: "*")]
public class TestController : ApiController
{
    // Controller methods not shown...
}

read more at : http://www.asp.net/web-api/overview/security/enabling-cross-origin-requests-in-web-api