Why isn't OnActivate being called? - wpf

Question

I'm asking this here because I'm at a loss for trying to figure this out. I've searched and all that comes up are things that make sense but also don't apply to my situation.
I'm using WPF with MVVM and Caliburn.Micro. I have a shell window with a corresponding view model which is a Conductor<Screen>.Collection.OnceActive and a screen which is inheriting from Screen. I'm calling ActivateItem within the Conductor's constructor to show the subsequent screen, it shows the screen correctly but never calls the Screen's override for OnActivate and the screen's IsActive property is set to False.
This only happens the very first time I call ActivateItem from the Conductor, all additional calls will properly call OnActivate and OnDeactivate.
This makes no sense to me and I have no idea what is going on. I cleaned the solution, rebuilt, and even rebooted but it still doesn't work properly. Below is the code:
Parent Conductor
[Export]
public sealed class ShellViewModel : Conductor<Screen>.Collection.OneActive, IHandle<SimpleMessage>
{
private readonly DashboardViewModel m_Dash;
private readonly LoginViewModel m_Login;
private readonly IEventAggregator m_MsgBus;
[ImportingConstructor]
public ShellViewModel(DashboardViewModel dash, LoginViewModel login, IEventAggregator msgBus)
{
this.m_MsgBus = msgBus;
this.m_Dash = dash;
this.m_Login = login;
this.ActivateItem(this.m_Login);
}
protected override void OnActivate()
{
this.m_MsgBus.Subscribe(this); //called correctly
}
protected override void OnDeactivate(bool close)
{
this.m_MsgBus.Unsubscribe(this); //called correctly
}
public void Handle(SimpleMessage message)
{
switch (message)
{
case SimpleMessage.LoginSuccess:
this.ActivateItem(this.m_Dash);
break;
case SimpleMessage.Logout:
this.ActivateItem(this.m_Login);
break;
}
}
}
Child Screen
[Export]
public sealed class LoginViewModel : Screen
{
private readonly IEventAggregator m_MsgBus;
[ImportingConstructor]
public LoginViewModel(IEventAggregator msgBus)
{
this.m_MsgBus = msgBus;
}
protected override void OnActivate()
{
//NOT called the first time, but is called every other time
MessageBox.Show("ACTIVATE TEST");
}
protected override void OnDeactivate(bool close)
{
//NOT called the first time, but is called every other time
MessageBox.Show("DEACTIVATE TEST");
}
public void CmdLogin(string password)
{
this.m_MsgBus.PublishOnUIThread(SimpleMessage.LoginSuccess);
}
public string Username { get; set; }
public string Password { get; set; }
}
UPDATE
I downloaded the Caliburn Micro source so I could step into the ActivateItem function and see what is going on. For some reason, when I first call ActivateItem from the Conductor the Conductor's IsActive property is set to false which causes Caliburn to skip calling the OnActivate override. I have no idea why the property would be false.
ConductorBaseWithActiveItem.cs
protected virtual void ChangeActiveItem(T newItem, bool closePrevious) {
ScreenExtensions.TryDeactivate(activeItem, closePrevious);
newItem = EnsureItem(newItem);
//Problem is here, IsActive is false the first time around in the conductor
if(IsActive)
ScreenExtensions.TryActivate(newItem);
activeItem = newItem;
NotifyOfPropertyChange("ActiveItem");
OnActivationProcessed(activeItem, true);
}
It looks like the reason IsActive is false in the Conductor is because my Conductor is the root view which is created using DisplayRootViewFor and it looks like that function does not set the IsActive property to true.
So, knowing that, am I simply just implementing this wrong and a Conductor can't/shouldn't be the root view? Do I need to have a 2nd child view which is the conductor (that seems like a bit much)?

Answer 1

I figured it out and it was basically me not thinking. Activating a view in the constructor of the conductor/root view doesn't work properly because it hasn't been activated yet. IsActive isn't set to true until the conductor's/root view's OnActivate is called.
This may be problematic at some point because the conductor isn't active even when OnInitialize is called and that is meant to be the one time init function and OnActivate could be called multiple times. In my case it will be fine because my conductor is the root view so OnActivate will only be called once.
Moral of the story is, don't call ActivateItem in a conductor's constructor when the conductor is a root view.