Add ViewModelBase.ViewModelState and OnInitialLoaded virtual method

StabilityMatrix.Avalonia/Models/ViewModelState.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace StabilityMatrix.Avalonia.Models;
+
+/// <summary>
+///
+/// </summary>
+[Flags]
+public enum ViewModelState : uint
+{
+    /// <summary>
+    /// View Model has been initially loaded
+    /// </summary>
+    InitialLoaded = 1 << 0,
+}

StabilityMatrix.Avalonia/ViewModels/Base/ViewModelBase.cs

@@ -2,12 +2,16 @@
 using System.Threading.Tasks;
 using AsyncAwaitBestPractices;
 using CommunityToolkit.Mvvm.ComponentModel;
+using JetBrains.Annotations;
 using StabilityMatrix.Avalonia.Models;
 
 namespace StabilityMatrix.Avalonia.ViewModels.Base;
 
 public class ViewModelBase : ObservableValidator, IRemovableListItem
 {
+    [PublicAPI]
+    protected ViewModelState ViewModelState { get; private set; }
+
     private WeakEventManager? parentListRemoveRequestedEventManager;
 
     public event EventHandler ParentListRemoveRequested
@@ -20,24 +24,51 @@ public class ViewModelBase : ObservableValidator, IRemovableListItem
         remove => parentListRemoveRequestedEventManager?.RemoveEventHandler(value);
     }
 
-    protected void RemoveFromParentList() => parentListRemoveRequestedEventManager?.RaiseEvent(
-        this, EventArgs.Empty, nameof(ParentListRemoveRequested));
+    protected void RemoveFromParentList() =>
+        parentListRemoveRequestedEventManager?.RaiseEvent(
+            this,
+            EventArgs.Empty,
+            nameof(ParentListRemoveRequested)
+        );
 
+    /// <summary>
+    /// Called when the view's LoadedEvent is fired.
+    /// </summary>
     public virtual void OnLoaded()
     {
-        
+        if (!ViewModelState.HasFlag(ViewModelState.InitialLoaded))
+        {
+            ViewModelState |= ViewModelState.InitialLoaded;
+            OnInitialLoaded();
+        }
     }
 
+    /// <summary>
+    /// Called the first time the view's LoadedEvent is fired.
+    /// Sets the <see cref="ViewModelState.InitialLoaded"/> flag.
+    /// </summary>
+    protected virtual void OnInitialLoaded() { }
+
+    /// <summary>
+    /// Called asynchronously when the view's LoadedEvent is fired.
+    /// Runs on the UI thread via Dispatcher.UIThread.InvokeAsync.
+    /// The view loading will not wait for this to complete.
+    /// </summary>
     public virtual Task OnLoadedAsync()
     {
         return Task.CompletedTask;
     }
 
-    public virtual void OnUnloaded()
-    {
-        
-    }
+    /// <summary>
+    /// Called when the view's UnloadedEvent is fired.
+    /// </summary>
+    public virtual void OnUnloaded() { }
 
+    /// <summary>
+    /// Called asynchronously when the view's UnloadedEvent is fired.
+    /// Runs on the UI thread via Dispatcher.UIThread.InvokeAsync.
+    /// The view loading will not wait for this to complete.
+    /// </summary>
     public virtual Task OnUnloadedAsync()
     {
         return Task.CompletedTask;