What conforming standards is this code violating?

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, DB开发者_开发问答sets.

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

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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.

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For one thing, by making the ViewModel a member of your controller, you really limit what you can do in a multi-threaded environment. If more than 1 of your Actions is invoked on the same controller, you may end up with a race condition to determine which of the passed-in view models is used for each view.

Edit: You get a different instance of the controller each time, so this will not happen. However, it is still something to keep in mind for other classes that use private members