假设你也有MVC路由，尝试在你的route.config中使用以下命令：

public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },
            constraints: new
            {
                // Add all routes we need MVC to handle here
                serverRoute = new ServerRouteConstraint(url =>
                {
                    return url.PathAndQuery.StartsWith("/qbo",
                        StringComparison.InvariantCultureIgnoreCase);
                })
            });

        // This is a catch-all for when no other routes matched. Let the Angular 2+ router take care of it
        routes.MapRoute(
            name: "angular",
            url: "{*url}",
            defaults: new { controller = "Home", action = "Index" } // The view that bootstraps Angular 2+
        );
    }

下面是路由约束类：

using System;
using System.Web;
using System.Web.Routing;

namespace Web
{
public class ServerRouteConstraint : IRouteConstraint
{
    private readonly Func<Uri, bool> _predicate;

    public ServerRouteConstraint(Func<Uri, bool> predicate)
    {
        this._predicate = predicate;
    }

    public bool Match(HttpContextBase httpContext, Route route, string parameterName,
        RouteValueDictionary values, RouteDirection routeDirection)
    {
        return this._predicate(httpContext.Request.Url);
    }
}
}

我已经使用这个很长一段时间了，不知道我可能是受到了哪个博客的启发。

我想明白了，不确定这是否是最好的方法，但它的工作。
我创建了一个名为FEController（FrontEndController）的控制器。

public ActionResult Index()
{
  return File(Server.MapPath("/app/") + "index.html", "text/html");
}

然后在RouteConfig.cs中添加Map路由

routes.MapRoute(
   "Angular",
   "{app}/{*pathInfo}",
   new { controller = "FE", action = "Index", id = UrlParameter.Optional }
);

routes.MapRoute(
   name: "Default",
   url: "api/{controller}/{action}/{id}",
   defaults: new { controller = "HelpMain", action = "Index", id = UrlParameter.Optional }
);

测试并确认工作正常。