ASP.NET MVC: No parameterless constructor defined for this object

Question

Server Error in '/' Application.
--------------------------------------------------------------------------------

No parameterless constructor defined for this object. 
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.MissingMethodException: No parameterless constructor defined for this object.

Source Error: 


Line 16:             HttpContext.Current.RewritePath(Request.ApplicationPath, false);
Line 17:             IHttpHandler httpHandler = new MvcHttpHandler();
Line 18:             httpHandler.ProcessRequest(HttpContext.Current);
Line 19:             HttpContext.Current.RewritePath(originalPath, false);
Line 20:         }

I was following Steven Sanderson's 'Pro ASP.NET MVC Framework' book. On page 132, in accordance with the author's recommendation, I downloaded the ASP.NET MVC Futures assembly, and added it to my MVC project. [Note: This could be a red herring.]

After this, I could no longer load my project. The above error stopped me cold.

My question is not, "Could you help me fix my code?"

Instead, I'd like to know more generally:

• How should I troubleshoot this issue?
• What should I be looking for?
• What might the root cause be?

It seems like I should understand routing and controllers at a deeper level than I do now.

Answer 1

I just had a similar problem. The same exception occurs when a Model has no parameterless constructor.

The call stack was figuring a method responsible for creating a new instance of a model.

System.Web.Mvc.DefaultModelBinder.CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType)

---

Here is a sample:

public class MyController : Controller
{
    public ActionResult Action(MyModel model)
    {

    }
}

public class MyModel
{
    public MyModel(IHelper helper) // MVC cannot call that
    {
        // ...
    }

    public MyModel() // MVC can call that
    {
    }
}