CaliburnMicro IEventAggregator won't work with ChildViews - wpf

Question

and sorry if this is a somewhat easy question, but I'm still new to CaliburnMicro and EventAggregator is proving to be the worst thing to learn by a long mile. Anyway, let's go to it. I have an app with a main ShellView and a bunch of ChildViews that display various information, and I need certain parameters to be shared between the Views. It did not take very long to find I need to use EventAggregator, but with Net6 I could not make it work, no chance. I found this app someone else did in Net3.1 and CaliburnMicro where a new window is created, on this second window there is a TextBox and a send button. Whatever you type here gets sended to the Main window. I studied the code and replicated the app succesfully, also with the latest version of Caliburn and Net6.
BUT then I decided to modify the app and instead of having a new window, now I have exactly the same but with a ChildView inside the ShellView, and here is where nothing works.
1st on the Bootstrapper
public class Bootstrapper : BootstrapperBase
{
private SimpleContainer _container;
public Bootstrapper()
{
Initialize();
}
protected override void Configure()
{
_container = new SimpleContainer();
_container.Singleton<IWindowManager, WindowManager>();
_container.Singleton<IEventAggregator, EventAggregator>();
_container.PerRequest<ShellViewModel>();
}
protected override object GetInstance(Type service, string key)
{
var instance = _container.GetInstance(service, key);
if (instance != null)
return instance;
throw new InvalidOperationException("Could not locate any instances.");
}
protected override IEnumerable<object> GetAllInstances(Type service)
{
return _container.GetAllInstances(service);
}
protected override void BuildUp(object instance)
{
_container.BuildUp(instance);
}
protected override void OnStartup(object sender, StartupEventArgs e)
{
DisplayRootViewFor<ShellViewModel>();
}
As seen, I've created a SimpleContainer, then initialised it as a Singleton.
Also _container.Singleton<IWindowManager, WindowManager>(); is no longer needed as I am not opening a new window anymore, so that could be commented but as I had so many issues, I let it be just in case for this last try before posting this question.
2nd I've created a class for the message IHandle to manage.
public class EventMessage
{
public string Text { get; set; }
}
3rd I created and edited the ChildViewModel (still called SecondWindowViewModel as this experiment is directly derivated from the original worknig one) and ChildView (well SecondWindowView still). Note that SecondWindowView is a WPF User Control, not a Window.
class SecondWindowViewModel : Screen
{
private readonly IEventAggregator _eventAggregator;
private string _secondTextBox;
public string SecondTextBox
{
get { return _secondTextBox; }
set { _secondTextBox = value; NotifyOfPropertyChange(() => SecondTextBox); }
}
public SecondWindowViewModel(IEventAggregator eventAggregator)
{
this._eventAggregator= eventAggregator;
}
public void SendBack()
{
EventMessage ToSend = new EventMessage();
ToSend.Text = SecondTextBox;
_eventAggregator.PublishOnUIThreadAsync(ToSend);
}
As seen, I have an IEventAggregator _eventAggregator, then on the constructor of the class I added this._eventAggregator= eventAggregator; and then on the method SendBack that is called upon pressing the button I send the message with SubscribeOnUIThread.
And lastly the ShellViewModel:
public class ShellViewModel : Conductor<Object>, IHandle<EventMessage>
{
private readonly IEventAggregator _eventAggregator;
private string _parentText;
public string ParentText
{
get { return _parentText; }
set { _parentText = value; NotifyOfPropertyChange(() => ParentText); }
}
public ShellViewModel(IEventAggregator eventAggregator)
{
ActivateItemAsync(new SecondWindowViewModel(_eventAggregator));
_eventAggregator = eventAggregator;
_eventAggregator.Subscribe(this);
}
public Task HandleAsync(EventMessage message, CancellationToken cancellationToken)
{
ParentText = message.Text;
return Task.CompletedTask;
}
//public void NewWindow()
//{
//WindowManager wm = new WindowManager();
//SecondWindowViewModel swm = new SecondWindowViewModel(_eventAggregator);
//wm.ShowWindowAsync(swm);
//}
}
}
Now here instead of inheriting from Screen and IScreen, I inherit from Conductor because I want to have that ChildView on my form. NewWindow is how it worked before but now that button no longer works as I don't need to launch a new window anymore, that's why it is commented out.
As seen, on the contructor I subscribe _eventAggregator, and then HandleAsync does the job of receiving the message and assign it to a variable. Now on the Caliburn Documentatin the method to use is public void Handle() but that no longer works, that's the only way I managed to make it work.
Now when I run this the app does load and seems to work just fine, but as soon as the SendBack() method gets called (in SecondWindowViewModel) the line _eventAggregator.PublishOnUIThreadAsync(ToSend); launches an exception System.NullReferenceException: 'Object reference not set to an instance of an object.'
From my understanding EventAggregator should not care if I'm sending the message to a Window or a user panel or anything. Only thnig I changed is commenting out NewWindow and deleting the old SecondWindowWiew WPF Window and replacing it with a new SecondWindowView WPF User Control with the exact same XAML, then in ShellWiev added bellow a <ContentControl x:Name="ActiveItem"/>.
I'm a bit of a loss here, I've been trying everything, coping the code from the documentation, looking for tutorials online, other StackOverflow questions, and while I could make the UI load and make HandleAsync work, for 3 days straight I could not make it work with ChildViews. That code I wrote does work with a new window. I even run into problems of ShellView straight up not loading unless putting a new constructor that takes no parameters and empty inside, but that's for another day.
Sorry for the extra long post, but I think it's important to put all the information out there. Thank you for your time and again, sorry if this is somewhat of a dumb question, but we all have to start somewhere no?