Fix browser issue with dispatcher used before initialization

src/Browser/Avalonia.Browser/BrowserAppBuilder.cs

@@ -58,6 +58,7 @@ public static class BrowserAppBuilder
             .AfterSetup(_ =>
             {
                 lifetime.View = new AvaloniaView(mainDivId);
+                lifetime.CompleteSetup();
             })
             .SetupWithLifetime(lifetime);
     }
@@ -77,6 +78,10 @@ public static class BrowserAppBuilder
 
         var lifetime = new BrowserSingleViewLifetime();
         builder
+            .AfterSetup(_ =>
+            {
+                lifetime.CompleteSetup();
+            })
             .SetupWithLifetime(lifetime);
     }
 

src/Browser/Avalonia.Browser/BrowserSingleViewLifetime.cs

@@ -13,26 +13,18 @@ internal class BrowserSingleViewLifetime : ISingleViewApplicationLifetime, IActi
 {
     public BrowserSingleViewLifetime()
     {
-        bool? initiallyVisible = InputHelper.SubscribeVisibilityChange(visible =>
+        _initiallyVisible = InputHelper.SubscribeVisibilityChange(visible =>
         {
-            initiallyVisible = null;
+            _initiallyVisible = null;
-            (visible ? Activated : Deactivated)?.Invoke(this, new ActivatedEventArgs(ActivationKind.Background));
+            var eventToTrigger = (visible ? Activated : Deactivated);
+            Dispatcher.UIThread.Invoke(
+                () => eventToTrigger?.Invoke(this, new ActivatedEventArgs(ActivationKind.Background)),
+                DispatcherPriority.Background);
         });
-
-        // Trigger Activated as an initial state, if web page is visible, and wasn't hidden during initialization.
-        if (initiallyVisible == true)
-        {
-            Dispatcher.UIThread.Invoke(() =>
-            {
-                if (initiallyVisible == true)
-                {
-                    Activated?.Invoke(this, new ActivatedEventArgs(ActivationKind.Background));
-                }
-            });
-        }
     }
     
     public AvaloniaView? View;
+    private bool? _initiallyVisible;
 
     public Control? MainView
     {
@@ -61,5 +53,17 @@ internal class BrowserSingleViewLifetime : ISingleViewApplicationLifetime, IActi
     public event EventHandler<ActivatedEventArgs>? Deactivated;
 
     public bool TryLeaveBackground() => false;
-    public bool TryEnterBackground() => true;
+    public bool TryEnterBackground() => false;
+
+    internal void CompleteSetup()
+    {
+        // Trigger Activated as an initial state, if web page is visible, and wasn't hidden during initialization.
+        Dispatcher.UIThread.Invoke(() =>
+        {
+            if (_initiallyVisible == true)
+            {
+                Activated?.Invoke(this, new ActivatedEventArgs(ActivationKind.Background));
+            }
+        }, DispatcherPriority.Background);
+    }
 }