Question

What is wrong with having a private ViewModel object, so that all my controller actions have access to it?

• I’m using EF4,MVC3,DBContext, DBsets.

  public class MyController {
  
  private MyViewModel _myViewModel;
  
  public ActionResult Index(MyViewModel myViewModel){ <-- There is a model Binder making this work
  
  _myViewModel = myViewModel;
  
  return _myViewModel;
  }
  
  }
  

Answer 1

Because everytime you call a controller action you get a different instance of the controller. So anything that you might have stored in instance fields of this controller from a previous action would be lost on subsequent actions. That’s the reason why in ASP.NET MVC you have notions such as Session, Application State, TempData, Cookies, Cache, … you name it.