more reactive UI work

Stars Assistant/ViewModels/MainWindowViewModel.cs

@@ -1,5 +1,8 @@
 using System.Collections.ObjectModel;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
 using ReactiveUI;
+using ReactiveUI.SourceGenerators;
 
 namespace StarsAssistant.ViewModels;
 
@@ -7,6 +10,24 @@ public partial class MainWindowViewModel : ViewModelBase, IActivatableViewModel
 {
     public ViewModelActivator Activator { get; } = new ViewModelActivator();
 
+    [ObservableAsProperty]
+    private string _welcomeMessage;
+
+    public MainWindowViewModel()
+    {
+        _welcomeMessage = "Lorem Ipsum";
+        _welcomeMessageHelper = Observable.Return("Dolor sit amet")
+            .ToProperty(this, x => x.WelcomeMessage);
+
+        this.WhenActivated((CompositeDisposable disposables) => 
+        {
+            // /* handle activation */
+            // Disposable
+            //     .Create(() => { /* handle deactivation */ })
+            //     .DisposeWith(disposables);
+        });
+    }        
+
     public ObservableCollection<PlanetViewModel> Planets { get; } = PlanetViewModel.LoadAll();
 
 }