Design : best practice to expose a CX ref class to Model ( which is in standard C++ ) ??

Question

Hi,

i have a view class and view-model class associated with it ( i am following the standard MVVM pattern)

the view and view-model are connected through the know "binding" practice.

the problem i have is how to connect the Model to the view-model ? 

i have my app-logic entirely in C++ ( so that i can reuse it in another platform) and i need some way to connect the

view-model and its corresponding Model object so that they could communicate with each other (through function calls and notifications ) 

i have built my own notification framework say , myNotificationClass, and the model uses this framework to publish the changes happening in it.

my question is what is the best practice followed in the such common situation by the view-model to subscribe to the model changes ? so as to keep the model independent from the C++/CX environment.

i tried the following - 

typedef std::function<void()> MyModelHandlerFunc_t;
class myModel
{
public:
   void AddHandler(MyModelHandlerFunc_t handler);
   void Notify()
   {
     clientHandler();
   }
private:
    MyModelHandlerFunc_t clientHandler;
}


public ref class myViewModelClient : public //some winRT class{
internal:	
        void myHandler();
        void SetUpModelHandler(myModel *model)
      {
         MyModelHandlerFunc_t handler = std::bind(&myHandler , this);
        model->AddHandler(handler);
      }
}

so that the Model just sees 

MyModelHandlerFunc_t

from its side.

but the above code is not compiling ( i expected this ) as we can't bind the C++/cx ref-class member function like 

MyModelHandlerFunc_t handler = std::bind(&myHandler , this);

so, my question is what is practice followed for such scenarios ?

how to "hide" the view-model details (meaning, try expose the ref class to the Model as normal C++ class object ) from the Model and make things work transparently b/w  Model and view-model ? 

---

Raj

Answer 1

I am not following what you are trying to do really but perhaps this will help.  Your object should support INotifyPropertyChanged.

This is an overview of the architecture:  http://msdn.microsoft.com/en-us/library/hh821028.aspx

and this should help too: http://www.bing.com/search?q=model+view+viewmodel

---

Jeff Sanders (MSFT)

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Answer 2

i seem to have figured out one solution.

in the view model - we can do the following 

void ViewModel::RegisterForModelNotification()
{         
    WeakReference wr(this);    
    auto notifHandler = [wr](){
             ViewModel^ vm = wr.Resolve<ViewModel>();                   
             vm->HandleModelNotification();       
         }  
   Model->RegisterObserver(notifHandler);
} 

---

Raj