paylink/samples/NewWebApplicationSample/Helpers/HMTLHelperExtensions.cs

using Microsoft.AspNetCore.Mvc.Rendering;

namespace NewWebApplicationSample
{
    public static class HtmlHelpers
    {
        public static string IsActive(this IHtmlHelper html, string controller = null, string action = null, string activeClass = "active")
        {
            var actualAction = (string)html.ViewContext.RouteData.Values["action"];
            var actualController = (string)html.ViewContext.RouteData.Values["controller"];

            if (string.IsNullOrEmpty(controller))
                controller = actualController;

            if (string.IsNullOrEmpty(action))
                action = actualAction;

            return (controller == actualController && action == actualAction) ? activeClass : string.Empty;
        }
    }
}