feat(ios): RequestedTheme will now affects KeyboardAppearance

src/SamplesApp/UITests.Shared/UITests.Shared.projitems

@@ -3245,6 +3245,10 @@
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
     </Page>
+    <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Input\Keyboard\Keyboard_iOS_Theme.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
     <Page Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Input\Keyboard\Keyboard_Showing_Dismissal.xaml">
       <SubType>Designer</SubType>
       <Generator>MSBuild:Compile</Generator>
@@ -6380,6 +6384,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Input\Keyboard\Keyboard_Events.xaml.cs">
       <DependentUpon>Keyboard_Events.xaml</DependentUpon>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Input\Keyboard\Keyboard_iOS_Theme.xaml.cs">
+      <DependentUpon>Keyboard_iOS_Theme.xaml</DependentUpon>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Windows_UI_Xaml_Input\Keyboard\Keyboard_Showing_Dismissal.xaml.cs">
       <DependentUpon>Keyboard_Showing_Dismissal.xaml</DependentUpon>
     </Compile>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Input/Keyboard/Keyboard_iOS_Theme.xaml

@@ -0,0 +1,63 @@
+<Page x:Class="UITests.Windows_UI_Xaml_Input.Keyboard.Keyboard_iOS_Theme"
+	  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+	  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+	  xmlns:local="using:UITests.Windows_UI_Xaml_Input.Keyboard"
+	  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+	  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+	  xmlns:ios="http://uno.ui/ios"
+	  mc:Ignorable="d ios"
+	  Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
+
+	<ScrollViewer>
+		<StackPanel>
+			<TextBlock Text="Requested Theme:" />
+			<Grid>
+				<Grid.ColumnDefinitions>
+					<ColumnDefinition Width="*" />
+					<ColumnDefinition Width="*" />
+					<ColumnDefinition Width="*" />
+				</Grid.ColumnDefinitions>
+
+				<RadioButton Grid.Column="0" Content="Default" Click="UpdateTheme" HorizontalAlignment="Stretch" />
+				<RadioButton Grid.Column="1" Content="Light" Click="UpdateTheme" HorizontalAlignment="Stretch" />
+				<RadioButton Grid.Column="2" Content="Dark" Click="UpdateTheme" HorizontalAlignment="Stretch" />
+			</Grid>
+
+			<TextBlock Text="KB Appearance: for 'custom' text/password-box" />
+			<Grid>
+				<Grid.ColumnDefinitions>
+					<ColumnDefinition Width="*" />
+					<ColumnDefinition Width="*" />
+					<ColumnDefinition Width="*" />
+				</Grid.ColumnDefinitions>
+
+				<RadioButton Grid.Column="0" Content="Default" Click="UpdateKeyboardAppearance" HorizontalAlignment="Stretch" />
+				<RadioButton Grid.Column="1" Content="Light" Click="UpdateKeyboardAppearance" HorizontalAlignment="Stretch" />
+				<RadioButton Grid.Column="2" Content="Dark" Click="UpdateKeyboardAppearance" HorizontalAlignment="Stretch" />
+			</Grid>
+			<TextBlock Text="note: Dark will be displayed as Alert because it shared the same value."
+					   TextWrapping="WrapWholeWords" />
+
+			<StackPanel x:Name="TestPanel">
+				<TextBlock Text="TextBox" Margin="0,20,0,0" />
+				<TextBox PlaceholderText="default" />
+				<TextBox PlaceholderText="light" ios:KeyboardAppearance="Light" />
+				<TextBox PlaceholderText="dark" ios:KeyboardAppearance="Dark" />
+				<TextBox PlaceholderText="custom:" />
+
+				<TextBlock Text="PasswordBox" Margin="0,20,0,0" />
+				<PasswordBox PlaceholderText="default" />
+				<PasswordBox PlaceholderText="light" ios:KeyboardAppearance="Light" />
+				<PasswordBox PlaceholderText="dark" ios:KeyboardAppearance="Dark" />
+				<PasswordBox PlaceholderText="custom:" />
+			</StackPanel>
+
+			<TextBlock TextWrapping="WrapWholeWords">
+				<Run>The 'device theme' can be changed by (ios)Settings &gt; Developer &gt; Dark Appearance.</Run><LineBreak /><LineBreak />
+				<Run>'default' should be affected by requested theme or os theme.</Run><LineBreak />
+				<Run>'dark/light' should always be that theme.</Run><LineBreak />
+				<Run>'custom' should be affected by 'KB Appearance', requested theme or os theme.</Run><LineBreak />
+			</TextBlock>
+		</StackPanel>
+	</ScrollViewer>
+</Page>

src/SamplesApp/UITests.Shared/Windows_UI_Xaml_Input/Keyboard/Keyboard_iOS_Theme.xaml.cs

@@ -0,0 +1,74 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Runtime.InteropServices.WindowsRuntime;
+using Uno.UI.Samples.Controls;
+using Windows.Foundation;
+using Windows.Foundation.Collections;
+using Windows.UI.Xaml;
+using Windows.UI.Xaml.Controls;
+using Windows.UI.Xaml.Controls.Primitives;
+using Windows.UI.Xaml.Data;
+using Windows.UI.Xaml.Input;
+using Windows.UI.Xaml.Media;
+using Windows.UI.Xaml.Navigation;
+
+namespace UITests.Windows_UI_Xaml_Input.Keyboard
+{
+	[SampleControlInfo("Keyboard", nameof(Keyboard_iOS_Theme),
+		description: Description,
+		ignoreInSnapshotTests: true,
+		isManualTest: true)]
+	public sealed partial class Keyboard_iOS_Theme : Page
+	{
+		private const string Description = "[iOS-only] Keyboard theme should be determined based on the following precedences: KeyboardAppearance > RequestedTheme > Device Theme.";
+
+		public Keyboard_iOS_Theme()
+		{
+			this.InitializeComponent();
+		}
+
+		private void UpdateTheme(object sender, RoutedEventArgs e)
+		{
+			var root = global::Windows.UI.Xaml.Window.Current.Content as FrameworkElement;
+			var theme = (sender as RadioButton).Content switch
+			{
+				"Light" => ElementTheme.Light,
+				"Dark" => ElementTheme.Dark,
+				"Default" => ElementTheme.Default,
+
+				_ => throw new ArgumentOutOfRangeException()
+			};
+
+			root.RequestedTheme = theme;
+		}
+
+		private void UpdateKeyboardAppearance(object sender, RoutedEventArgs e)
+		{
+#if __IOS__
+			var appearance = (sender as RadioButton).Content switch
+			{
+				"Light" => UIKit.UIKeyboardAppearance.Light,
+				"Dark" => UIKit.UIKeyboardAppearance.Dark,
+				"Default" => UIKit.UIKeyboardAppearance.Default,
+
+				_ => throw new ArgumentOutOfRangeException()
+			};
+			foreach (var item in TestPanel.Children.OfType<FrameworkElement>())
+			{
+				if (item is TextBox tbox && tbox.PlaceholderText?.StartsWith("custom") == true)
+				{
+					tbox.PlaceholderText = $"custom: {appearance}";
+					tbox.KeyboardAppearance = appearance;
+				}
+				else if (item is PasswordBox pbox && pbox.PlaceholderText?.StartsWith("custom") == true)
+				{
+					pbox.PlaceholderText = $"custom: {appearance}";
+					pbox.KeyboardAppearance = appearance;
+				}
+			}
+#endif
+		}
+	}
+}

src/Uno.UI/UI/Xaml/Application.cs

@@ -44,7 +44,6 @@ public partial class Application
 	{
 		private bool _initializationComplete = false;
 		private readonly static IEventProvider _trace = Tracing.Get(TraceProvider.Id);
-		private bool _themeSetExplicitly = false;
 		private ApplicationTheme? _requestedTheme;
 		private bool _systemThemeChangesObserved = false;
 		private SpecializedResourceDictionary.ResourceKey _requestedThemeForResources;
@@ -159,10 +158,12 @@ private set
 			_ => throw new InvalidOperationException("Application's RequestedTheme is invalid."),
 		};
 
+		internal bool IsThemeSetExplicitly { get; private set; } = false;
+
 		internal void SetExplicitRequestedTheme(ApplicationTheme? explicitTheme)
 		{
 			// this flag makes sure the app will not respond to OS events
-			_themeSetExplicitly = explicitTheme.HasValue;
+			IsThemeSetExplicitly = explicitTheme.HasValue;
 			var theme = explicitTheme ?? GetDefaultSystemTheme();
 			SetRequestedTheme(theme);
 		}
@@ -202,7 +203,7 @@ internal void SetExplicitRequestedTheme(ApplicationTheme? explicitTheme)
 		public void OnSystemThemeChanged()
 		{
 			// if user overrides theme, don't apply system theme
-			if (!_themeSetExplicitly)
+			if (!IsThemeSetExplicitly)
 			{
 				var theme = GetDefaultSystemTheme();
 				SetRequestedTheme(theme);

src/Uno.UI/UI/Xaml/Controls/PasswordBox/PasswordBox.iOSmacOS.cs

@@ -6,6 +6,8 @@ namespace Windows.UI.Xaml.Controls
 {
 	public partial class PasswordBox : TextBox
 	{
+		// TODO: copy UpdateThemeBindings+UpdateKeyboardThemePartial impl when PasswordBox no longer inherits from TextBox
+
 		partial void SetPasswordScope(bool shouldHideText)
 		{
 			SetSecureTextEntry(shouldHideText);

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.cs

@@ -854,5 +854,14 @@ public void Select(int start, int length)
 		partial void SelectAllPartial();
 
 		internal override bool CanHaveChildren() => true;
+
+		internal override void UpdateThemeBindings()
+		{
+			base.UpdateThemeBindings();
+
+			UpdateKeyboardThemePartial();
+		}
+
+		partial void UpdateKeyboardThemePartial();
 	}
 }

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.iOS.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using Uno.UI;
 using Windows.UI.Xaml.Data;
@@ -27,6 +28,7 @@ public partial class TextBox
 			OnTextAlignmentChanged(CreateInitialValueChangerEventArgs(TextAlignmentProperty, null, TextAlignment));
 			OnReturnKeyTypeChanged(ReturnKeyType);
 			OnKeyboardAppearanceChanged(KeyboardAppearance);
+			UpdateKeyboardThemePartial();
 		}
 
 		partial void OnFocusStateChangedPartial(FocusState focusState)
@@ -334,5 +336,35 @@ private void OnKeyboardAppearanceChanged(UIKeyboardAppearance newValue)
 		}
 
 		#endregion
+
+		partial void UpdateKeyboardThemePartial()
+		{
+			if (_textBoxView == null) return;
+
+			// if KeyboardAppearance has been explicitly set, we leave it as is.
+			if (KeyboardAppearance != UIKeyboardAppearance.Default) return;
+
+			ElementTheme? GetExplicitlySetAppTheme() => Application.Current.IsThemeSetExplicitly
+				? Application.Current.ActualElementTheme as ElementTheme?
+				: null;
+
+			// the appearance will be determined by the first parent/self that has a non-default RequestedTheme,
+			// or the explicitly requested application theme.
+			// note: the literal "Default" value is lost on the ActualTheme property, which is why we are not using it here.
+			var theme = VisualTreeHelper.EnumerateAncestors(this).OfType<FrameworkElement>()
+				.Prepend(this)
+				.Select(x => x.RequestedTheme as ElementTheme?)
+				.Append(GetExplicitlySetAppTheme())
+				.FirstOrDefault(x => x != ElementTheme.Default);
+			var appearance = theme switch
+			{
+				ElementTheme.Light => UIKeyboardAppearance.Light,
+				ElementTheme.Dark => UIKeyboardAppearance.Dark,
+
+				_ => UIKeyboardAppearance.Default
+			};
+
+			_textBoxView.KeyboardAppearance = appearance;
+		}
 	}
 }

src/Uno.UI/UI/Xaml/Media/VisualTreeHelper.cs

@@ -510,6 +510,15 @@ internal static UIElement SearchDownForLeaf(UIElement root, Predicate<UIElement>
 			return root;
 		}
 
+		internal static IEnumerable<DependencyObject> EnumerateAncestors(DependencyObject o)
+		{
+			while ((o as FrameworkElement)?.Parent is { } parent)
+			{
+				yield return parent;
+				o = parent;
+			}
+		}
+
 		#region Helpers
 		private static Func<IEnumerable<UIElement>, IEnumerable<UIElement>> Except(UIElement element)
 			=> children => children.Except(element);