c# - Deal with collections in model in WPF MVVM

Question

I've started to learn WPF\MVVM approach and get bit confused. I've:

class ModelAAA {
    public List<Foo> Foos{get; protected set;}
    //..

    public void Boo()
    {
       //Some complex logic updating Foos
    }
}

class ViewModelAAA{

    private ModelAAA _modelAAA

    public ObservableCollection<Foo> Foos{get; protected set;}

    public void ViewModelAAA(ModelAAA modelAAA)
    {
        this._modelAAA = modelAAA;
        this.Foos = new ObservableCollection(modelAAA.Foos)
    }

    public void Boo()
    {
       this._modelAAA.Boo();
       //What should I do here?
    }
}

So if I use Boo method of view model, what is proper view to update collection in ViewModel. I've got few ideas, but they all seems to by ugly. Should I manauly recreate\change viewModel Foos each time? As I understad ObservableCollection is not wrapper like object.

P.S. I'm want to make it whitout using ObservableCollection in model

Answer 1

No, you do not need manually change it, as this is ObservableCollection, but you are changing original collection and not observable one.

To notify listeners of your Observable you need to act on Observable itself.

Example:

public void Boo()
{
   this.Foos.Boo();

}

Answer 2

Your Model does not need to use ObservableCollection, but has to notify your ViewModel that something changed in the Collection.

this creates a copy of your List, which is indeed observable, but is not changed at all after that:

this.Foos = new ObservableCollection(modelAAA.Foos);

I would not recommend to create a new ObservableCollection, each time the Model-Collection changed. Instead implement the INotifyCollectionChanged in your Model-Collection and handle the events in your Viewmodel properly.