Is there a difference between ModelState and ViewData.ModelState?

Question

In some ASP.NET MVC code examples, I see references to ModelState.IsValid, and in other examples I see references to ViewData.ModelState.IsValid.

In my initial research, I see:

• ModelState is a public property in Controller class.
• ViewData is a public property in ControllerBase class.

Is there a difference between the two? Why have both?

Answer 1

They reference the exact same thing, if you look at the code for System.Web.Mvc.Controller class you will see the implementation for ModelState is:

   public ModelStateDictionary ModelState
    {
      get
      {
        return this.ViewData.ModelState;
      }
    }

I would say it is simply there for easy of use in your own Controller implementations.