Caliburn Micro Screen Derived View Model Support Sub View Models? - windows-runtime

Question

Using Caliburn Micro v2 is there a way of composing view models inside a screen such that the child view models get the OnInitialize, OnActivate() and OnDeactivate(bool) calls?
I have something like the following view model WidgetsViewModel used to display a screen.
public class WidgetsViewModel : Screen, IHandle<WidgetUpdateEvent>
{
public ObservableCollection<WidgetSummaryViewModel> Widgets { get; set; }
...
public void Handle(WidgetUpdateEvent theEvent)
{
// Update the specific widget in Widgets collection
}
}
public class WidgetSummaryViewModel
{
public int Counter { get; set; }
}
I would like to move the handling of the WidgetUpdateEvent into the WidgetSummaryViewModel where it would sit more comfortably. Something like this:
public class WidgetSummaryViewModel : IHandle<WidgetUpdateEvent>
{
public int Counter { get; set; }
public WidgetSummaryViewModel(IEventAggregator theEventAggregator)
{
theEventAggregator.Subscribe(this);
}
public void Handle(WidgetUpdateEvent theEvent)
{
// Update this view model...
}
}
What makes me uncomfortable is calling Subscribe inside the view model constructor. It would be much better if the screen was able to call the OnInitialize, OnActivate and OnDeactivate for me as it does for Screen derived view models. Is there some way to compose sub view models inside a screen derived based view model?

Answer 1

Make WidgetsViewModel a conductor:
public class WidgetsViewModel : Conductor<WidgetSummaryViewModel>.Collection.AllActive
{
}
Update your data binding in WidgetsView:
{Binding Items} instead of {Binding Widgets}
Derive WidgetSummaryViewModel from Screen and override all the methods you need.
For further information regarding Conductors, visit Screens, Conductors and Composition.