WPF + MvvM + Prism

Question

I am new in the Wpf & Mvvm world , but I have found a couple of examples and just found that there is some different way to instantiate the model. I would like to know the b

Answer 1

What you got there makes sense and in both cases is a View-first approach to creating a viewmodel. I.e. the view creates the ViewModel. In the original example the viewmodel is created outside of the view (and is sometimes referred to as marriage pattern), but as far as I am concerned that's the same thing - creation of the view creates the ViewModel.

If this suits your needs stick with it. Another approach you might look into is ViewModel first where the viewmodel takes a dependency on the view like so:

//In the bare-bones(i.e. no WPF dependencies) common interface assembly

interfac IView {
  void ApplyViewModel(object viewmodel);
}    

interface IMainView : IView {
  //this interface can actually be empty.
  //It's only used to map to implementation.
}

//In the ViewModel assembly

class MainViewModel {
  public MainViewModel(IMainView view) {
    view.ApplyViewModel(this);
  }
}

public partial class MainView : UserControl, IMainView {
  void ApplyViewModel(object viewmodel){
    DataContext = viewmodel;
  }
}

Then you can inject this view like so:

IRegion region = regionManager.Regions["MainRegion"];

//This might look strange as we are resolving the class to itself, not an interface to the class
//This is OK, we want to take advantage of the DI container 
//to resolve the viewmodel's dependencies for us,
//not just to resolve an interface to the class.
MainViewModel mainViewModel = container.Resolve();

region.Add(mainViewModel.View, "MainView");
region.Activate(ordersView.View);