caliburn.micro Condutor not working

Question 1

Our Solution for that Problem is to remove the use Screen as BaseClass for DocViewerViewModel an implement the Conductor Logic our self.

Question 2

As far as I can tell, there is nothing wrong with the way your code is written. Since you are using MVVM, I suggest you design a test case like I've provided here.

And here's a snippet of the test case

// TestHarness.cs

[TestMethod]
public void CheckDeactivation()
{
    // We'd like to have the ToolViewerViewModel only Conduct the dock-able views 
    // and the DocViewerViewModel to conduct the DocumentViewModel.

    IViewModelFactory factory = new ViewModelFactory();
    DocViewerViewModel docViewer = new DocViewerViewModel(factory);
    IDockManager dockManager = null;

    var toolViewer = new ToolViewerViewModel(factory, docViewer, dockManager);
    var mockToolView = new UserControl();           
    (toolViewer as IViewAware).AttachView(mockToolView);

    DocumentViewModel docView1 = new NoDataViewModel();
    DocumentViewModel docView2 = new NoDataViewModel();
    docViewer.ActivateItem(docView1);
    docViewer.ActivateItem(docView2);

    Assert.AreEqual(0, docViewer.CountDeactivated());
}

Question 3

I have had the exact same problem as you, and ended up using PropertyChangedBase instead of Screen and got the problem to disappear. Later, after reading the docs on Screens and Conductors here, I realized that I wasn't activating the conductor itself further up in the view hierarchy!

So have a look at wherever you use your ToolViewerViewModel, and make sure you activate that instance!

Question 4

Thank you very much for your Test. Even thought it is really nice code it tests the wrong code part. Your code simply tests whether the Method ActivateItem() or DeactivateItem() is being called:

public override void ActivateItem(DocumentViewModel item)
{
    _countActivated++;
    base.ActivateItem(item);
}

public override void DeactivateItem(DocumentViewModel item, bool close)
{
     _countDeactivated++;
     base.DeactivateItem(item, close);
}

But since these Methods are being called explicitly we don't need to test for that...

The real Problem is that the Conductor is not calling the OnActivate() or OnDeactivate() on the DocumentViewModel class. To enhance your test I used the following code:

public class DummyViewModelFactory : IViewModelFactory
{
    private readonly Dictionary<Type, Func<object>> _registredCreators = new Dictionary<Type, Func<object>>();

    public T Create<T>() where T : PropertyChangedBase
    {
        return Create(typeof(T)) as T;
    }

    public object Create(Type type)
    {
        if (type == null)
        {
            return null;
        }

        if (_registredCreators.ContainsKey(type))
        {
            return _registredCreators[type]();
        }

        return null;
    }

    public void Release(object instance)
    {
    }

    public void RegisterCreatorFor<T>(Func<T> creatorFunction)
    {
        _registredCreators.Add(typeof(T), () => creatorFunction());
    }
}

As concrete DocumentViewModel implementation I made:

public class NoDataViewModel : DocumentViewModel
{
    public NoDataViewModel(IEventAggregator eventAggregator,
        IViewModelFactory viewModelFactory)
        : base(viewModelFactory, eventAggregator, )
    {
    }

    public override void Save()
    {
        // nothing to do
    }

    public override void Reload()
    {
        // nothing to do
    }
}

public class NoDataViewModelMock : NoDataViewModel
{
    private static int activationCounterForTesting = 0;
    private static int deactivationCounterForTesting = 0;

    public static int ActivationCounterForTesting
    {
        get
        {
            return activationCounterForTesting;
        }
    }

    public static int DeactivationCounterForTesting
    {
        get
        {
            return deactivationCounterForTesting;
        }
    }

    public NoDataViewModelMock()
        : base(null, null)
    {
    }

    protected override void OnActivate()
    {
        activationCounterForTesting++;
        base.OnActivate();
    }

    protected override void OnDeactivate(bool close)
    {
        deactivationCounterForTesting++;
        base.OnDeactivate(close);
    }
}

And I changed your Testmethod to this:

[TestMethod]
public void CheckDeactivation()
{
    var viewModelFactory = new DummyViewModelFactory();

    viewModelFactory.RegisterCreatorFor<NoDataViewModel>(() => new NoDataViewModelMock());

    var docViewer = new DocViewerViewModel(viewModelFactory);
    IDockManager dockManager = null;

    var toolViewer = new ToolViewerViewModel(viewModelFactory, docViewer, dockManager);
    var mockToolView = new UserControl();
    (toolViewer as IViewAware).AttachView(mockToolView);

    docViewerViewModel.ShowInMainView<NoDataViewModel>();
    docViewerViewModel.ShowInMainView<NoDataViewModel>();
    docViewerViewModel.ShowInMainView<NoDataViewModel>();

    Assert.AreEqual(3, NoDataViewModelMock.ActivationCounterForTesting);
    Assert.AreEqual(2, NoDataViewModelMock.DeactivationCounterForTesting);
}

Then you'll see that the OnActivate() and OnDeactivate() methods are never been called.

With a little more advanced test you'd also see that they are being called but from the ToolViewerViewModel directly. I'd like to know why and how I can change this behavior to fit my needs:

The DocumentViewModel.OnActivate() method should get called when the DocViewerViewModel.ShowInMainView<T>() method gets called.
The DocumentViewModel.OnDeactivate() method should get called on the old DocumentViewModel when a new one is being shown by calling the DocViewerViewModel.ShowInMainView<T>()