ViewModel和Model并观察更改

Question

Should ViewModels be associated with other ViewModels and interact with them or should only be allowed to interact with Models? Or a mix of both?

I'll try to be more explicit with code:

Is this code OK?

public class MainViewModel
{
    public MainViewModel(IPeopleService service)
    {
        var people = service.GetPeople();
        People = new ObservableCollection<PersonViewModel>(people.Select(p => new PersonViewModel(p)));
    }

    public ObservableCollection<PersonViewModel> People { get; set; }
    public PersonViewModel SelectedPerson { get; set; }
}

You see the SelectedPerson is a ViewModel, not the Model.

Answer 1

A ViewModel can interact with the other viewmodels , but not the way you did. In your scenerio MainViewModel depends on PersonViewModel. This is wrong approach and it should be Person model.

If you want to interact with ViewModels and transfer data between them, you should use mediator pattern. Many popular MVVM frameworks have this capability and it's called Messenger service.

Edit: Here is a sample code. I generally use MVVM Light, but you can use whatever you want.

 public class MainViewModel
{
    public MainViewModel(IPeopleService service)
    {
        var people = service.GetPeople();
        People = new ObservableCollection<Person>(people.Select(p => new Person(p)));
    }

    public ObservableCollection<Person> People { get; set; }

    private Person _person;
    public Person SelectedPerson
    {
        get
        {
            return _person;
        }
        set
        {
            if(value != null)
            {
                _person = value;
                OnPropertyChanged("SelectedPerson");
                //Send selected person on each change
                Messenger.Default.Send<Person>(_person);
            }
        }
    }
}

In your PersonViewModel, you should register for messages type of Person:

 public class PersonViewModel
{
    private Person _person;
    public Person SelectedPerson
    {
        get
        {
            return _person;
        }
        set
        {
            if (value != null)
            {
                _person = value;
                OnPropertyChanged("SelectedPerson");                    
            }
        }
    }
    public PersonViewModel()
    {
        Messenger.Default.Register<Person>(this, (p) =>
            {
                SelectedPerson = p;
            });
    }
}