feat(focus): Add support for FindLastFocusableElement

src/Uno.UI/Extensions/UIViewExtensions.iOSmacOS.cs

@@ -206,6 +206,25 @@ public static IEnumerable<_View> FindSubviews(this _View view, Func<_View, bool>
 			}
 		}
 
+		public static IEnumerable<_View> FindSubviewsReverse(this _View view, Func<_View, bool> selector, int maxDepth = 20)
+		{
+			for (int i = view.Subviews.Length - 1; i >= 0; i--)
+			{
+				var sub = view.Subviews[i];
+				if (selector(sub))
+				{
+					yield return sub;
+				}
+				else if (maxDepth > 0)
+				{
+					foreach (var subResult in sub.FindSubviewsReverse(selector, maxDepth - 1))
+					{
+						yield return subResult;
+					}
+				}
+			}
+		}
+
 		/// <summary>
 		/// Enumerates all the children for a specified view.
 		/// </summary>

src/Uno.UI/Extensions/ViewExtensions.Android.cs

@@ -128,8 +128,8 @@ public static IEnumerable<View> GetParents(this View view)
 		/// <summary>
 		/// Gets an enumerator containing all the children of a View group
 		/// </summary>
-		/// <param name="group"></param>
-		/// <returns></returns>
+		/// <param name="group">View group</param>
+		/// <returns>Children in default order</returns>
 		public static IEnumerable<View> GetChildren(this ViewGroup group)
 		{
 			var shadowProvider = group as Controls.IShadowChildrenProvider;
@@ -146,6 +146,33 @@ public static IEnumerable<View> GetChildren(this ViewGroup group)
 			}
 		}
 
+		/// <summary>
+		/// Gets an reverse enumerator containing all the children of a View group
+		/// </summary>
+		/// <param name="group">View group</param>
+		/// <returns>Children in reverse order</returns>
+		public static IEnumerable<View> GetChildrenReverse(this ViewGroup group)
+		{
+			var shadowProvider = group as Controls.IShadowChildrenProvider;
+
+			if (shadowProvider != null)
+			{
+				// To avoid calling ChildCount/GetChildAt too much during enumeration, use
+				// a fast path that relies on a shadowed list of the children in BindableView.
+				for (int i = shadowProvider.ChildrenShadow.Count - 1; i >= 0; i--)
+				{
+					yield return shadowProvider.ChildrenShadow[i];
+				}
+			}
+			else
+			{
+				foreach (var child in GetChildrenReverseSlow(group))
+				{
+					yield return child;
+				}
+			}
+		}
+
 		/// <summary>
 		/// Finds the first child <see cref="View"/> of the provided <see cref="ViewGroup"/>.
 		/// </summary>
@@ -188,6 +215,19 @@ private static IEnumerable<View> GetChildrenSlow(ViewGroup group)
 			}
 		}
 
+		/// <summary>
+		/// A reverse enumerator for ViewGroup children that uses interop calls.
+		/// </summary>
+		private static IEnumerable<View> GetChildrenReverseSlow(ViewGroup group)
+		{
+			var count = group.ChildCount;
+
+			for (int i = count - 1; i >= 0; i++)
+			{
+				yield return group.GetChildAt(i);
+			}
+		}
+
 		/// <summary>
 		/// Gets a filtered enumerator containing children of the view group
 		/// </summary>
@@ -236,6 +276,36 @@ public static IEnumerable<View> EnumerateAllChildren(this ViewGroup view, Func<V
 			}
 		}
 
+		/// <summary>
+		/// Enumerates all the children for a specified view group in reverse order.
+		/// </summary>
+		/// <param name="view">The view group to get the children from</param>
+		/// <param name="selector">The selector function</param>
+		/// <param name="maxDepth">The depth to stop looking for children.</param>
+		/// <returns>A lazy enumerable of views in reverse order</returns>
+		public static IEnumerable<View> EnumerateAllChildrenReverse(this ViewGroup view, Func<View, bool> selector, int maxDepth = 20)
+		{
+			foreach (var sub in view.GetChildrenReverse())
+			{
+				if (selector(sub))
+				{
+					yield return sub;
+				}
+				else if (maxDepth > 0)
+				{
+					var childGroup = sub as ViewGroup;
+
+					if (childGroup != null)
+					{
+						foreach (var subResult in childGroup.EnumerateAllChildrenReverse(selector, maxDepth - 1))
+						{
+							yield return subResult;
+						}
+					}
+				}
+			}
+		}
+
 		/// <summary>
 		/// Enumerates all the children for a specified view group.
 		/// </summary>

src/Uno.UI/UI/Xaml/Input/FocusManager.Android.cs

@@ -214,24 +214,34 @@ public static View InnerFindNextFocusableElement(FocusNavigationDirection focusN
 			}
 		}
 
-		public static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
+		private static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
 		{
 			if (searchScope == null)
 			{
 				searchScope = Window.Current.Content;
 			}
 
-			if (IsFocusableView(searchScope as View))
+			if (!(searchScope is ViewGroup searchViewGroup))
+			{
+				return null;
+			}
+
+			return searchViewGroup.EnumerateAllChildren(IsFocusableView, maxDepth: 300).FirstOrDefault() as DependencyObject;			
+		}
+
+		private static DependencyObject InnerFindLastFocusableElement(DependencyObject searchScope)
+		{
+			if (searchScope == null)
 			{
-				return searchScope;
+				searchScope = Window.Current.Content;
 			}
 
 			if (!(searchScope is ViewGroup searchViewGroup))
 			{
 				return null;
 			}
 
-			return searchViewGroup.EnumerateAllChildren(IsFocusableView, maxDepth: 300).FirstOrDefault() as DependencyObject;			
+			return searchViewGroup.EnumerateAllChildrenReverse(IsFocusableView, maxDepth: 300).FirstOrDefault() as DependencyObject;
 		}
 
 		private static void FocusNative(Control control)

src/Uno.UI/UI/Xaml/Input/FocusManager.cs

@@ -50,7 +50,7 @@ public static UIElement FindNextFocusableElement(FocusNavigationDirection focusN
 		}
 
 		/// <summary>
-		/// Retrieves the first element that can receive focus based on the specified scope.
+		/// Retrieves the last element that can receive focus based on the specified scope.
 		/// </summary>
 		/// <param name="searchScope">The root object from which to search. If null, the search scope is the current window.</param>
 		/// <returns>The first focusable object.</returns>
@@ -59,6 +59,16 @@ public static DependencyObject FindFirstFocusableElement(DependencyObject search
 			return InnerFindFirstFocusableElement(searchScope);
 		}
 
+		/// <summary>
+		/// Retrieves the last element that can receive focus based on the specified scope.
+		/// </summary>
+		/// <param name="searchScope">The root object from which to search. If null, the search scope is the current window.</param>
+		/// <returns>The first focusable object.</returns>
+		public static DependencyObject FindLastFocusableElement(DependencyObject searchScope)
+		{
+			return InnerFindLastFocusableElement(searchScope);
+		}
+
 		internal static bool SetFocusedElement(DependencyObject newFocus, FocusNavigationDirection focusNavigationDirection, FocusState focusState)
 		{
 			var control = newFocus as Control; // For now only called for Control

src/Uno.UI/UI/Xaml/Input/FocusManager.iOS.cs

@@ -208,7 +208,7 @@ public static UIView InnerFindNextFocusableElement(FocusNavigationDirection focu
 			}
 		}
 
-		public static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
+		private static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
 		{
 			if (searchScope == null)
 			{
@@ -220,12 +220,22 @@ public static DependencyObject InnerFindFirstFocusableElement(DependencyObject s
 				return null;
 			}
 
-			if (IsFocusableView(searchView))
+			return searchView.FindSubviews(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
+		}
+
+		private static DependencyObject InnerFindLastFocusableElement(DependencyObject searchScope)
+		{
+			if (searchScope == null)
+			{
+				searchScope = Window.Current.Content;
+			}
+
+			if (!(searchScope is UIView searchView))
 			{
-				return searchScope;
+				return null;
 			}
 
-			return searchView.FindSubviews(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
+			return searchView.FindSubviewsReverse(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
 		}
 
 		private static void FocusNative(Control control) => control.BecomeFirstResponder();

src/Uno.UI/UI/Xaml/Input/FocusManager.macOS.cs

@@ -213,7 +213,7 @@ public static NSView InnerFindNextFocusableElement(FocusNavigationDirection focu
 			}
 		}
 
-		public static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
+		private static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
 		{
 			if (searchScope == null)
 			{
@@ -225,12 +225,22 @@ public static DependencyObject InnerFindFirstFocusableElement(DependencyObject s
 				return null;
 			}
 
-			if (IsFocusableView(searchView))
+			return searchView.FindSubviews(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
+		}
+
+		private static DependencyObject InnerFindLastFocusableElement(DependencyObject searchScope)
+		{
+			if (searchScope == null)
+			{
+				searchScope = Window.Current.Content;
+			}
+
+			if (!(searchScope is NSView searchView))
 			{
-				return searchScope;
+				return null;
 			}
 
-			return searchView.FindSubviews(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
+			return searchView.FindSubviewsReverse(selector: IsFocusableView, maxDepth: 100).FirstOrDefault() as DependencyObject;
 		}
 
 		private static void FocusNative(Control control) => control.BecomeFirstResponder();

src/Uno.UI/UI/Xaml/Input/FocusManager.net.cs

@@ -50,6 +50,11 @@ public static DependencyObject InnerFindFirstFocusableElement(DependencyObject s
 			throw new NotImplementedException();
 		}
 
+		private static DependencyObject InnerFindLastFocusableElement(DependencyObject searchScope)
+		{
+			throw new NotImplementedException();
+		}
+
 		public static void OnFocusChanged(View control, FocusState state)
 		{
 			throw new NotImplementedException();

src/Uno.UI/UI/Xaml/Input/FocusManager.wasm.cs

@@ -114,7 +114,12 @@ private static UIElement InnerFindNextFocusableElement(FocusNavigationDirection
 			return null;
 		}
 
-		public static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
+		private static DependencyObject InnerFindFirstFocusableElement(DependencyObject searchScope)
+		{
+			return null;
+		}
+
+		private static DependencyObject InnerFindLastFocusableElement(DependencyObject searchScope)
 		{
 			return null;
 		}