Owin.IAppBuilder在asp.net中不包含“MapSignalR”错误的定义

Owin.IAppBuilder’ does not contain a definition for ‘MapSignalR’ and
no extension method ‘MapSignalR’ accepting a first argument of type
‘Owin.IAppBuilder’ could be found (are you missing a using directive
or an assembly reference?)

这是我的代码

using System;
 using System.Threading.Tasks;
 using Microsoft.Owin;
 using Owin;

 [assembly: OwinStartup(typeof(VirtualClassroom.Startup1))]

 namespace VirtualClassroom
 {
     public class Startup1
        {
           public void Configuration(IAppBuilder app)
               {
                    app.MapSignalR();

               }
        }

}
我搜索了很多,并尝试按堆栈溢出答案
???‘Owin.IAppBuilder’ does not contain a definition for ‘MapSignalR’我有

1.新增Microsoft.Owin //版本2.0.1

2.添加了Microsoft.Owin.Security //版本2.0.1

3.增加了Microsoft Asp.Net SignalR

但我仍然得到同样的错误.请帮忙.提前致谢！！