Question

Have been learning about MVP and have tried writing a test app using it in WinForms. I’m struggling to find a well explained example on how to navigate between my forms/views. As an example, the program starts and I want to show a login dialog then go into my main view if the login was successful. At the moment, my Main method looks something like this:

static void Main()
{
   var loginView = Injector.Resolve<ILoginView>();
   if (loginView.DoLogin() != LoginResult.OK) return;
   var mainView = Injector.Resolve<IMainView>();
   Application.Run(mainView); // won't work as mainView isn't a form
}

The Injector object is just a wrapper around an IoC tool (currently StructureMap). The thing is, I’ve read that I shouldn’t really be manually creating instances via the Injector as they should really be done via constructor injection.

I’ve managed to do this up to a point but not when it comes to navigation. I can’t think of an elegant way of moving through my views and was wondering if anyone here might shed some light on this? I’ve read a little on application controllers but have not found an example to show it clearly.

Answer 1

In regards to the navigation question:

I’ve managed to do this up to a point but not when it comes to
navigation. I can’t think of an elegant way of moving through my views
and was wondering if anyone here might shed some light on this? I’ve
read a little on application controllers but have not found an example
to show it clearly.

Below is a simplified version of a construct I’ve used. Note that the setup and tear down hooks are called automatically when the NavigateTo method is called. Also, +1 to @AlexBurtsev, as his answer hints at this very same approach.

// Presenter can and should offer common services for the
// subclasses 
abstract class Presenter
{

   public void Display()
   {
      OnDisplay();
   }

   public void Dismiss()   
   {
      OnDismiss();
   }


   protected virtual OnDisplay() // hook for subclass
   {   
   }

   protected virtual OnDismiss() // hook for subclass
   {   
   }

   private NavigationManager _navMgr;

   internal NavigationMgr NavigationManager
   {   
      get
      {
         return _navMgr;
      }
      set
      {
         _navMgr = value;
      }

   }

}

// NavigationManager is used to transition (or navigate) 
// between views
class NavigationManager
{

   Presenter _current;

   // use this override if your Presenter are non-persistent (transient)
   public void NavigateTo(Type nextPresenterType, object args)
   {   
      Presenter nextPresenter = Activator.CreateInstance(nextPresenterType);   
      NavigateTo(nextPresenter);   
   }

   // use this override if your Presenter are persistent (long-lived)
   public void NavigateTo(Presenter nextPresenter, object args)
   {
      if (_current != null)
      {
         _current.Dismiss()
         _current.NavigationMgr = null;
         _current = null;
      }

      if (nextPresenter != null)
      {
         _current = nextPresenter;
         _current.NavigationMgr = this;
         _current.Display(args);
      }         
   }

}


class MainMenuPresenter : Presenter
{

   private IMainMenuView _mainMenuView = null;

   // OnDisplay is your startup hook
   protected override void OnDisplay()
   {
      // get your view from where ever (injection, etc)
      _mainMenuView = GetView();      

      // configure your view
      _mainMenuView.Title = GetMainTitleInCurrentLanguage();
      // etc      
      // etc

      // listen for relevent events from the view
      _mainMenuView.NewWorkOrderSelected += new EventHandler(MainMenuView_NewWorkOrderSelected);

      // display to the user
      _mainMenuView.Show();
   }

   protected override void OnDismiss()
   {
      // cleanup
      _mainMenuView.NewWorkOrderSelected -= new EventHandler(MainMenuView_NewWorkOrderSelected);
      _mainMenuView.Close();
      _mainMenuView = null;
   }

   // respond to the various view events
   private void MainMenuView_NewWorkOrderSelected(object src, EventArgs e)
   {
      // example of transitioning to a new view here...
      NavigationMgr.NavigateTo(NewWorkOrderPresenter, null);            
   }

}


class NewWorkOrderPresenter : Presenter
{

   protected override void OnDisplay()
   {
      // get the view, configure it, listen for its events, and show it
   }

   protected override void OnDismiss()
   {
      // unlisten for events and release the view
   }

}