ASP.NET MVC 4项目 - Razor intellisense已经丢失

I've recently updated an ASP.NET MVC project from v3 to v4, and now my .cshtml Razor views have lost intellisense when edited in Visual Studio. Keywords and helper properties such as @model, @Url, @Html etc. are not being recognised and are producing errors in VS. When ran, the app itself works fine.I've recently updated an ASP.NET MVC project fr