fix: hot reload ios support for navigationbar (#1354)

* fix: hot reload ios support for navigationbar

* chore: do not render when unloaded

* chore: wip

* chore: wip

* chore: unhook from element in renderer

* chore: undo uno bump

* chore: fix unloaded event unhook

Author: kazo0

src/Uno.Toolkit.UI/Controls/NavigationBar/NativeNavigationBarPresenter.iOS.cs

@@ -60,13 +60,12 @@ private void OnUnloaded(object sender, RoutedEventArgs e)
 		partial void OnOwnerChanged()
 		{
 			// TODO: Find a proper way to decide whether a NavigationBar exists on canvas (within Page), or is mapped to the UINavigationController's NavigationBar.
-
 			_mainCommandClickHandler.Disposable = null;
 
 			if (GetNavBar() is { } navBar)
 			{
 				navBar.MainCommand.Click += OnMainCommandClick;
-				
+
 				_mainCommandClickHandler.Disposable = Disposable.Create(() => navBar.MainCommand.Click -= OnMainCommandClick);
 
 				LayoutNativeNavBar(navBar);
@@ -75,6 +74,21 @@ partial void OnOwnerChanged()
 
 		private void LayoutNativeNavBar(NavigationBar navBar)
 		{
+			var page = navBar.FindFirstParent<Page>();
+			var parent = page?.Parent as Page;
+			if (page is not null
+				&& parent?.GetType() == page.GetType())
+			{
+				// Support for Hot Reload
+				// On iOS, the current Page instance is retained and its Content is replaced with a new instance of the Page
+				// If we detect that we have fallen into this scenario, hook up the new NavigationBar from within the new Page instance
+				// to the native UINavigationBar and UINavigationItem instances.
+				var vc = parent.FindViewController();
+
+				NavigationBarHelper.SetNavigationItem(navBar, vc.NavigationItem);
+				NavigationBarHelper.SetNavigationBar(navBar, vc.NavigationController?.NavigationBar);
+			}
+
 			if (navBar.TryGetNative<NavigationBar, NavigationBarRenderer, UINavigationBar>(out var nativeBar)
 				&& nativeBar is { })
 			{

src/Uno.Toolkit.UI/Controls/NavigationBar/Renderer.cs

@@ -37,6 +37,9 @@ internal abstract class Renderer<TElement, TNative> : IDisposable
 			where TNative : class
 	{
 		private CompositeDisposable _subscriptions = new CompositeDisposable();
+#if __IOS__
+		private SerialDisposable _unloadedSubscription = new SerialDisposable();
+#endif
 		private readonly WeakReference<TElement> _element;
 		private TNative? _native;
 		private bool _isRendering;
@@ -48,9 +51,28 @@ public Renderer(TElement element)
 				throw new ArgumentNullException(nameof(element));
 			}
 
+#if __IOS__
+			if (element is FrameworkElement fe)
+			{
+				fe.Unloaded += OnElementUnloaded;
+				_unloadedSubscription.Disposable = Disposable.Create(() =>
+				{
+					fe.Unloaded -= OnElementUnloaded;
+				});
+			}
+#endif
+
 			_element = new WeakReference<TElement>(element);
 		}
 
+#if __IOS__
+		private void OnElementUnloaded(object sender, RoutedEventArgs? e)
+		{
+			_unloadedSubscription.Dispose();
+			Dispose();
+		}
+#endif
+
 		public TElement? Element
 		{
 			get