Caliburn ShowDialog and MessageBox

Question

I\'m making a small demo application for MVVM with caliburn.

Now I want to show a MessageBox, but the MVVM way.

For dialogs I created an event, that

Answer 1

When the root/main/shell view-model implements a kind of DialogService interface, every other view-model needing to show dialogs will end up with a dependency on the root view-model. Sometimes this might not be desiderable, e.g. if it could cause a dependency loop:
DialogService (aka RootViewModel) -> SomeViewModel -> RootViewModel.

A more involved approach to break this dependency chain (and actually invert it) is the following:

• Implement a behavior that detects Window.OnSourceInitialized event and attach it to main view Window component. That is the event fired when the window handle is available. Upon event, behavior will notify some handler passed in via attached property:

public class WindowSourceBehavior : Behavior
{
  // ...
  // boilerplate code for IWindowListener InitListener dependency property
  // ...

  attachedWindow.SourceInitialized += (sender, evt) =>
  {
     // ...
     InitListener.SourceInitialized(sender as Window);
  }
}

• DialogService exposes a handler - or interface - as requested by behavior:

public class DialogService : IWindowListener
{
  // ...
  public void SourceInitialized(Window rootWindow) { /* ... */ }
}

• In root view-model, (indirectly) get the DialogService injected as a dependency. During construction, sets view-model bound property, WindowListener, to the DialogService handler/interface:

public MainViewModel(IWindowListener dialogServiceInDisguise)
{
  WindowListener = dialogServiceInDisguise;
}

public IWindowListener WindowListener { get; private set; }

Doing so, the DialogService is able to get a hold of root Window, and whichever view-model needs to show a dialog does not create a(n indirect) dependency on main view-model.