Conductor<T>'s ActiveItem not Updating View

Problem

I am using Caliburn Micro in WPF on Windows / desktop.

I have the following very simple ShellView.xaml:

<ContentControl Caliburn:View.Model="{Binding ActiveItem}"/>

I am using a Conductor<IViewModelBase> to display the ActiveItem.

My ShellViewModel.cs (Conductor) looks like this:

    internal sealed class ShellViewModel : Conductor<IViewModelBase>, IShellViewModel
    {
        private readonly IMainViewModel mainViewModel;

        public ShellViewModel(IWelcomeViewModel welcomeViewModel, IMainViewModel mainViewModel)
        {
            this.mainViewModel = mainViewModel;

            welcomeViewModel.Deactivated += WelcomeViewModel_Deactivated;
            ChangeActiveItem(welcomeViewModel, false); // <-- Initial ActiveItem
        }

        private void WelcomeViewModel_Deactivated(object sender, DeactivationEventArgs e)
        {
            ((IWelcomeViewModel)sender).Deactivated -= WelcomeViewModel_Deactivated;
            ChangeActiveItem(mainViewModel, true); // <-- Changes ActiveItem to MainViewModel
        }
    }

For the purposes of testing, WelcomeViewModel TryClose()-s after 10 seconds:

    internal class WelcomeViewModel : ViewModelBase, IWelcomeViewModel
    {
        public WelcomeViewModel()
        {
            Timer timer = new Timer(10_000) { Enabled = true };
            timer.Elapsed += (sender, e) => TryClose();
            timer.Start();
        }
    }

The expected result is that the view should update its UserControl to match whichever ViewModel has been bound to, which is the ActiveItem, which changes after 10 seconds. However, it doesn’t - the screen becomes blank (white).

Attempted Solutions

I’ve tried swapping the two ViewModels around - having the MainViewModel go first - and in that case, the MainViewModel is displayed, however the screen does not end up displaying WelcomeViewModel; it goes blank instead.

Subsequently, I tried manually notifying of change.

NotifyOfPropertyChange(() => ActiveItem);

This also did not work.

I have also tried using convention binding on the ShellView.xaml (x:Name="ActiveItem") which also did not work.

Finally, I remember once having to activate my conductor (Conductor<T>.Collection.OneActive) in order for it to properly activate/deactivate views, so I tried that as well (in ShellViewModel.cs):

ScreenExtensions.TryActivate(this);

also to no avail.

What worked, however, was having a custom IViewModelBase property (e.g. ActiveView), and binding to that instead, changing it whenever ChangeActiveItem is called.

Question

I can, of course, fix this issue by either rolling my own ActiveItem, or not using Conductor<T> at all, however I would like to do this properly.

Is there some kind of trick to using Conductor<T>, or is this just a bug? I have searched plenty on the internet and nothing seemed to work.

[Aleksbgbg]

Okay, thanks for all the help. You can close the issue if you wish.

[nigel-sampson]

From what I can tell there’s a bit of a race condition happening here. Calling TryClose on WelcomeViewModel will deactivate that view model, and remove it from being the ActiveItem. However by listening for that event and jumping in the middle we’re trying to replace the ActiveItem before the previously one is finished being closed.