如果您正在使用API，请将这一行添加到您的方法中。

HttpContext.Current.Response.AddHeader("Access-Control-Allow-Origin", "*"); 

本教程非常有用。简单总结一下:

使用Nuget上提供的CORS包:Install-Package Microsoft.AspNet.WebApi.Cors 在WebApiConfig.cs文件中，将config.EnableCors()添加到Register()方法中。 为你需要处理cors的控制器添加一个属性:

[EnableCors(origins: "<origin address in here>"， headers: "*"， methods: "*")]

这非常简单，只需将其添加到web.config中

<system.webServer>
  <httpProtocol>
    <customHeaders>
      <add name="Access-Control-Allow-Origin" value="http://localhost" />
      <add name="Access-Control-Allow-Headers" value="X-AspNet-Version,X-Powered-By,Date,Server,Accept,Accept-Encoding,Accept-Language,Cache-Control,Connection,Content-Length,Content-Type,Host,Origin,Pragma,Referer,User-Agent" />
      <add name="Access-Control-Allow-Methods" value="GET, PUT, POST, DELETE, OPTIONS" />
      <add name="Access-Control-Max-Age" value="1000" />
    </customHeaders>
  </httpProtocol>
</system.webServer>

在Origin中输入所有可以访问你的网络服务器的域名， 在header中放入任何ajax HTTP请求可以使用的所有可能的header， 在方法中，把你允许的所有方法放在你的服务器上

的问候:)

    public ActionResult ActionName(string ReqParam1, string ReqParam2, string ReqParam3, string ReqParam4)
    {
        this.ControllerContext.HttpContext.Response.Headers.Add("Access-Control-Allow-Origin","*");
         /*
                --Your code goes here --
         */
        return Json(new { ReturnData= "Data to be returned", Success=true }, JsonRequestBehavior.AllowGet);
    }

有时OPTIONS动词也会引起问题

简单: 更新你的网页。配置如下

<system.webServer>
    <httpProtocol>
        <customHeaders>
          <add name="Access-Control-Allow-Origin" value="*" />
          <add name="Access-Control-Allow-Headers" value="Origin, X-Requested-With, Content-Type, Accept" />
        </customHeaders>
    </httpProtocol>
</system.webServer>

用httpGet和httpOptions更新webservice/controller头

// GET api/Master/Sync/?version=12121
        [HttpGet][HttpOptions]
        public dynamic Sync(string version) 
        {

After struggling for a whole evening I finally got this to work. After some debugging I found the problem I was walking into was that my client was sending a so called preflight Options request to check if the application was allowed to send a post request with the origin, methods and headers provided. I didn't want to use Owin or an APIController, so I started digging and came up with the following solution with just an ActionFilterAttribute. Especially the "Access-Control-Allow-Headers" part is very important, as the headers mentioned there do have to match the headers your request will send.

using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace MyNamespace
{
    public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpRequest request = HttpContext.Current.Request;
            HttpResponse response = HttpContext.Current.Response;

            // check for preflight request
            if (request.Headers.AllKeys.Contains("Origin") && request.HttpMethod == "OPTIONS")
            {
                response.AppendHeader("Access-Control-Allow-Origin", "*");
                response.AppendHeader("Access-Control-Allow-Credentials", "true");
                response.AppendHeader("Access-Control-Allow-Methods", "GET, PUT, POST, DELETE");
                response.AppendHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, X-RequestDigest, Cache-Control, Content-Type, Accept, Access-Control-Allow-Origin, Session, odata-version");
                response.End();
            }
            else
            {
                HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.NoCache);
                HttpContext.Current.Response.Cache.SetNoStore();

                response.AppendHeader("Access-Control-Allow-Origin", "*");
                response.AppendHeader("Access-Control-Allow-Credentials", "true");
                if (request.HttpMethod == "POST")
                {
                    response.AppendHeader("Access-Control-Allow-Methods", "GET, PUT, POST, DELETE");
                    response.AppendHeader("Access-Control-Allow-Headers", "Origin, X-Requested-With, X-RequestDigest, Cache-Control, Content-Type, Accept, Access-Control-Allow-Origin, Session, odata-version");
                }

                base.OnActionExecuting(filterContext);
            }
        }
    }
}

最后，我的MVC动作方法看起来像这样。这里重要的是还要提到Options HttpVerbs，否则preflight请求将失败。

[AcceptVerbs(HttpVerbs.Post | HttpVerbs.Options)]
[AllowCrossSiteJson]
public async Task<ActionResult> Create(MyModel model)
{
    return Json(await DoSomething(model));
}