asp.net mvc web api 可跨域方法

<location path="Sample.txt">
<system.webServer>
<httpProtocol>
<customHeaders>
<add name="Access-Control-Allow-Origin" value="*" />
</customHeaders>
</httpProtocol>
</system.webServer>
</location>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

using System;
using System.Web.Http.Filters;

namespace Workflow.Filters
{
public class AllowCrossSiteJsonAttribute : ActionFilterAttribute
{
public override void OnActionExecuted(HttpActionExecutedContext actionExecutedContext)
{
if (actionExecutedContext.Response != null)
actionExecutedContext.Response.Headers.Add("Access-Control-Allow-Origin", "*");

base.OnActionExecuted(actionExecutedContext);
}
}
}

[AllowCrossSiteJson]
public class InstancesController : ApiController
{
// ......

}