我使用 Visual Studio 15 創建了一個應用程序，使用 ASP.NET Web api 作為后端，在前端使用 Angular 6。我只是想根據數據庫中的數據在前端顯示/添加/刪除用戶。我使用 Angular 6 中的 HttpClient 和 GET-Request 來顯示用戶數據工作正常。我嘗試以相同的方式實現 POST/DELETE 請求。這是來自 Angular 的調用：deleteUser(id: number): Observable<{}> {    const url = `${this.userURL}/${id}`;    return this.http.delete(url, { withCredentials: true })        .pipe(            catchError(this.handleError('deleteData'))        );}web API：我在 Global.asax.cs 中處理了預檢請求：void Application_PreSendRequestHeaders(Object sender, EventArgs e)    {        var origin = Request.Headers.Get("Origin");        var validOrigins = ConfigurationManager.AppSettings["allowedCorsOrigins"].Split(',');        if (validOrigins.Any(o => o == origin))        {            Response.StatusCode = (int)HttpStatusCode.OK;            Response.Headers.Set("Access-Control-Allow-Origin", origin);            Response.Headers.Set("Access-Control-Allow-Credentials", "true");            Response.Headers.Set("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, access-control-allow-credentials, access-control-allow-headers, access-control-allow-methods, access-control-allow-origin, ontent-type, Origin, Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers, Authorization"); // "Content-Type, Accept, Authorization, withcredentials, Prefer"            Response.Headers.Set("Access-Control-Expose-Headers", "Claims, *");            Response.Headers.Set("Access-Control-Allow-Methods", "GET,PUT,POST,OPTIONS,PATCH,DELETE");        }    }