Question

I have an ASP.NET page that implements my view and creates the presenter in the page constuctor. Phil Haack s post providing was used as the starting point, and I ll just the examples from the post to illustrate the question.

public partial class _Default : System.Web.UI.Page, IPostEditView {

    PostEditController controller;
    public _Default()
    {
         this.controller = new PostEditController(this, new BlogDataService());
    }
}

What is the best approach to inject the instance of the BlogDataService? The examples I have found use properties in the Page class for the dependency marked with an attribute which the injection framework resolves.

However, I prefer using the constructor approach for testing purposes.

Does anyone have input or perhaps links to good implementations of the above. I would prefer Ninject, but StructureMap or Windsor would be fine as long as its fluent.

Thanks for any feedback.

Answer 1

If you use the Microsoft ServiceLocator, you can apply the service locator design pattern and ask the container for the service.

In your case it would look something like this:

public partial class _Default : System.Web.UI.Page, IPostEditView {

    PostEditController controller;
    public _Default()
    {
         var service = ServiceLocator.Current.GetInstance<IBlogDataService>();
         this.controller = new PostEditController(this, service);
    }
}

ServiceLocator has implementations for Castle Windsor and StructureMap. Not sure about Ninject, but it s trivial to create a ServiceLocator adapter for a new IoC.

Answer 2

In our homegrown MVP-framework we had a typed base-class that all Pages inherited from. The type needed to be of type Presenter (our base presenter class)

In the base-class we then initialized the controller using the IoC-container.

Sample code:

public class EditPage : BasePage<EditController> {
}

public class EditController : Presenter {
 public EditController(IService service) { }
}

public class BasePage<T> : Page where T: Presenter
{
 T Presenter { get; set; }
 public BasePage() { 
  Presenter = ObjectFactory.GetInstance<T>(); //StructureMap
 }
}

Hope this helps!

Answer 3

I haven t seen a general purpose method for doing constructor injection on webforms. I assume it may be possible via a PageFactory implementation, but since most on the edge right now are moving to MVC rather than webforms, that may not happen.

However, autofac (a DI container I like a lot) has an integration module for ASP.NET WebForms that does property injection without attributes - your code would look like this :

public partial class _Default : System.Web.UI.Page, IPostEditView {

    public IBlogDataService DataService{get;set;}
    public _Default()
    {
    }
}

I know this doesn t specifically solve your desire to use constructor injection, but this is the closest I know of.

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