خطای CORE

چگونه خطای زیر را برطرف کنیم؟

Access to XMLHttpRequest at 'http://localhost:2569/api/contact' from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

core.js:1449 ERROR HttpErrorResponse {headers: HttpHeaders, status: 0, statusText: "Unknown Error", url: null, ok: false, …}

defaultErrorLogger @ core.js:1449

ErrorHandler.handleError @ core.js:1510

next @ core.js:5508

schedulerFn @ core.js:4342

SafeSubscriber.__tryOrUnsub @ Subscriber.js:240

SafeSubscriber.next @ Subscriber.js:187

Subscriber._next @ Subscriber.js:128

Subscriber.next @ Subscriber.js:92

Subject.next @ Subject.js:56

EventEmitter.emit @ core.js:4322

(anonymous) @ core.js:4782

ZoneDelegate.invoke @ zone.js:388

Zone.run @ zone.js:138

NgZone.runOutsideAngular @ core.js:4708

onHandleError @ core.js:4782

ZoneDelegate.handleError @ zone.js:392

Zone.runTask @ zone.js:191

ZoneTask.invokeTask @ zone.js:495

invokeTask @ zone.js:1536

globalZoneAwareCallback @ zone.js:1562

error (async)

customScheduleGlobal @ zone.js:1662

ZoneDelegate.scheduleTask @ zone.js:407

Zone.scheduleTask @ zone.js:232

Zone.scheduleEventTask @ zone.js:258

(anonymous) @ zone.js:1841

desc.set @ zone.js:1232

WebSocketTransport @ sockjs.js:2974

SockJS._connect @ sockjs.js:828

SockJS._receiveInfo @ sockjs.js:802

g @ sockjs.js:66

EventEmitter.emit @ sockjs.js:86

(anonymous) @ sockjs.js:567

g @ sockjs.js:66

EventEmitter.emit @ sockjs.js:86

(anonymous) @ sockjs.js:374

g @ sockjs.js:66

EventEmitter.emit @ sockjs.js:86

xhr.onreadystatechange @ sockjs.js:1593

wrapFn @ zone.js:1176

ZoneDelegate.invokeTask @ zone.js:421

Zone.runTask @ zone.js:188

ZoneTask.invokeTask @ zone.js:495

invokeTask @ zone.js:1536

globalZoneAwareCallback @ zone.js:1562

XMLHttpRequest.send (async)

scheduleTask @ zone.js:2975

ZoneDelegate.scheduleTask @ zone.js:407

Zone.scheduleTask @ zone.js:232

Zone.scheduleMacroTask @ zone.js:255

(anonymous) @ zone.js:3008

proto.(anonymous function) @ zone.js:1382

AbstractXHRObject._start @ sockjs.js:1601

(anonymous) @ sockjs.js:1490

ZoneDelegate.invokeTask @ zone.js:421

Zone.runTask @ zone.js:188

ZoneTask.invokeTask @ zone.js:495

ZoneTask.invoke @ zone.js:484

timer @ zone.js:2065

setTimeout (async)

scheduleTask @ zone.js:2087

ZoneDelegate.scheduleTask @ zone.js:407

Zone.scheduleTask @ zone.js:232

Zone.scheduleMacroTask @ zone.js:255

(anonymous) @ zone.js:2103

proto.(anonymous function) @ zone.js:1382

AbstractXHRObject @ sockjs.js:1489

XHRLocalObject @ sockjs.js:2910

InfoAjax @ sockjs.js:356

InfoReceiver._getReceiver @ sockjs.js:536

InfoReceiver.doXhr @ sockjs.js:556

(anonymous) @ sockjs.js:525

ZoneDelegate.invokeTask @ zone.js:421

Zone.runTask @ zone.js:188

ZoneTask.invokeTask @ zone.js:495

ZoneTask.invoke @ zone.js:484

timer @ zone.js:2065

setTimeout (async)

scheduleTask @ zone.js:2087

ZoneDelegate.scheduleTask @ zone.js:407

Zone.scheduleTask @ zone.js:232

Zone.scheduleMacroTask @ zone.js:255

(anonymous) @ zone.js:2103

proto.(anonymous function) @ zone.js:1382

InfoReceiver @ sockjs.js:524

SockJS @ sockjs.js:730

socket @ socket.js:9

(anonymous) @ client:200

(anonymous) @ client:242

../../../../webpack-dev-server/client/index.js?http://0.0.0.0:0 @ vendor.bundle.js:1390

__webpack_require__ @ inline.bundle.js:55

0 @ main.bundle.js:232

__webpack_require__ @ inline.bundle.js:55

webpackJsonpCallback @ inline.bundle.js:26

(anonymous) @ main.bundle.js:1

جالب است در قسمت BackEnd WebAPI در web.config کد زیر را اضافه کرده ام:

<httpProtocol>

    <customHeaders>

      <add name="Access-Control-Allow-Origin" value="*" />

      <add name="Access-Control-Allow-Headers" value="Content-Type" />

      <add name="Access-Control-Allow-Methods" value="GET, POST, PUT, DELETE, OPTIONS" />

    </customHeaders>

  </httpProtocol>

در ASP.NET Core برای فعال سازی CORS باید سرویس و میان افزار اون رو اضافه کنید.

public void ConfigureServices(IServiceCollection services)

{

    services.AddCors();

}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)

{

    loggerFactory.AddConsole();



    if (env.IsDevelopment())

    {

        app.UseDeveloperExceptionPage();

    }



    // Shows UseCors with CorsPolicyBuilder.

    app.UseCors(builder =>

       builder.WithOrigins("http://example.com"));



    app.Run(async (context) =>

    {

        await context.Response.WriteAsync("Hello World!");

    });

}    

middle ware رو اد کن

سلام
متاسفانه با این کدها هم همچنان همان خطا را میدهد
راه حل نداره؟