.net浏览器跨域问题,出现错误

No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3739' is therefore not allowed access.

这种问题怎么解决？网上都说在页面添加 Response.AddHeader("Access-Control-Allow-Origin",“* "）
添加到哪？在代码里也找不到 Access-Control-Allow-Origin

context.Response.ClearHeaders();
context.Response.AppendHeader("Access-Control-Allow-Origin","*");
string requestHeaders = context.Request.Headers["Access-Control-Request-Headers"];
context.Response.AppendHeader("Access-Control-Allow-Headers",
string.IsNullOrEmpty(requestHeaders) ? "*" : requestHeaders);
context.Response.AppendHeader("Access-Control-Allow-Methods", "POST, OPTIONS")；

context.Response.ClearHeaders();
context.Response.AppendHeader("Access-Control-Allow-Origin","*");
string requestHeaders = context.Request.Headers["Access-Control-Request-Headers"];
context.Response.AppendHeader("Access-Control-Allow-Headers",
string.IsNullOrEmpty(requestHeaders) ? "*" : requestHeaders);
context.Response.AppendHeader("Access-Control-Allow-Methods", "POST, OPTIONS")；