1 – 自定义操作过滤器,如果用户已登录,则会从页面重定向用户.

public class RedirectAuthenticatedRequests : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if(filterContext.HttpContext.Request.IsAuthenticated) {
            filterContext.Result = new RedirectToRouteResult(
                new RouteValueDictionary(new {
                        controller = "SomeController",action = "SomeAction"
                }
            ));
        }

        base.OnActionExecuting(filterContext);
    }
}

2 – 如果用户已登录,请简单检查登录操作方法.

if(Request.IsAuthenticated) return RedirectToAction("SomeOtherView");