[Windows] Replace Header with PlaceholderText for Title property of Picker

src/Controls/tests/DeviceTests/Elements/Picker/PickerTests.Windows.cs

@@ -6,8 +6,10 @@
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Platform;
+using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Xunit;
+using WSolidColorBrush = Microsoft.UI.Xaml.Media.SolidColorBrush;
 
 namespace Microsoft.Maui.DeviceTests
 {
@@ -56,6 +58,179 @@ public async Task VerticalOptionsInitializesCorrectly()
 			await InvokeOnMainThreadAsync(() => Assert.Equal(UI.Xaml.VerticalAlignment.Bottom, GetPlatformVerticalOptions(handler.PlatformView)));
 		}
 
+		[Fact(DisplayName = "Title maps to PlaceholderText")]
+		public async Task TitleMapsToPlaceholderText()
+		{
+			var picker = new Picker()
+			{
+				Title = "Select Option",
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				Assert.Equal("Select Option", handler.PlatformView.PlaceholderText);
+			});
+		}
+
+		[Fact(DisplayName = "Null title maps to empty PlaceholderText")]
+		public async Task NullTitleMapsToEmptyPlaceholderText()
+		{
+			var picker = new Picker()
+			{
+				Title = null,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				Assert.Equal(string.Empty, handler.PlatformView.PlaceholderText);
+			});
+		}
+
+		[Fact(DisplayName = "Empty title maps to empty PlaceholderText")]
+		public async Task EmptyTitleMapsToEmptyPlaceholderText()
+		{
+			var picker = new Picker()
+			{
+				Title = string.Empty,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				Assert.Equal(string.Empty, handler.PlatformView.PlaceholderText);
+			});
+		}
+
+		[Fact(DisplayName = "TitleColor maps to PlaceholderForeground")]
+		public async Task TitleColorMapsToPlaceholderForeground()
+		{
+			var picker = new Picker()
+			{
+				Title = "Select Option",
+				TitleColor = Colors.Red,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				var placeholderBrush = Assert.IsType<WSolidColorBrush>(handler.PlatformView.PlaceholderForeground);
+				Assert.Equal(Colors.Red, placeholderBrush.Color.ToColor());
+			});
+		}
+
+		[Fact(DisplayName = "Null TitleColor clears local PlaceholderForeground")]
+		public async Task NullTitleColorClearsPlaceholderForegroundLocalValue()
+		{
+			var picker = new Picker()
+			{
+				Title = "Select Option",
+				TitleColor = Colors.Red,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				Assert.IsType<WSolidColorBrush>(handler.PlatformView.PlaceholderForeground);
+
+				picker.ClearValue(Picker.TitleColorProperty);
+
+				Assert.Equal(DependencyProperty.UnsetValue, handler.PlatformView.ReadLocalValue(ComboBox.PlaceholderForegroundProperty));
+			});
+		}
+
+		[Fact(DisplayName = "Title and TitleColor update after handler creation")]
+		public async Task TitleAndTitleColorUpdateAfterHandlerCreation()
+		{
+			var picker = new Picker()
+			{
+				Title = "First",
+				TitleColor = Colors.Red,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				}
+			};
+
+			var handler = await CreateHandlerAsync<PickerHandler>(picker);
+
+			await InvokeOnMainThreadAsync(() =>
+			{
+				picker.Title = "Second";
+				Assert.Equal("Second", handler.PlatformView.PlaceholderText);
+
+				picker.TitleColor = Colors.Blue;
+				var brush = Assert.IsType<WSolidColorBrush>(handler.PlatformView.PlaceholderForeground);
+				Assert.Equal(Colors.Blue, brush.Color.ToColor());
+			});
+		}
+
+		[Fact(DisplayName = "CharacterSpacing applies to placeholder TextBlock when Title is set")]
+		public async Task CharacterSpacingAppliesToPlaceholderWithTitle()
+		{
+			const string title = "Select Option";
+			const double characterSpacingPt = 8d;
+			var expectedEm = characterSpacingPt.ToEm();
+
+			var picker = new Picker()
+			{
+				Title = title,
+				CharacterSpacing = characterSpacingPt,
+				ItemsSource = new ObservableCollection<string>()
+				{
+					"Item 1",
+					"Item 2"
+				},
+				WidthRequest = 200,
+				HeightRequest = 48
+			};
+
+			await AttachAndRun<PickerHandler>(picker, handler =>
+			{
+				var platformView = handler.PlatformView;
+
+				Assert.Equal(title, platformView.PlaceholderText);
+				Assert.Equal(expectedEm, platformView.CharacterSpacing);
+
+				var placeholderTextBlock = platformView.GetDescendantByName<TextBlock>("PlaceholderTextBlock");
+				Assert.NotNull(placeholderTextBlock);
+				Assert.Equal(title, placeholderTextBlock.Text);
+				Assert.Equal(expectedEm, placeholderTextBlock.CharacterSpacing);
+			});
+		}
+
 		protected Task<string> GetPlatformControlText(ComboBox platformView)
 		{
 			return InvokeOnMainThreadAsync(() =>

src/Core/src/Handlers/Picker/PickerHandler.Windows.cs

@@ -69,7 +69,7 @@ public static void MapTitle(IPickerHandler handler, IPicker picker)
 
 		public static void MapTitleColor(IPickerHandler handler, IPicker picker)
 		{
-			handler.PlatformView?.UpdateTitle(picker);
+			handler.PlatformView?.UpdateTitleColor(picker);
 		}
 
 		public static void MapBackground(IPickerHandler handler, IPicker picker)

src/Core/src/Platform/Windows/PickerExtensions.cs

@@ -9,11 +9,16 @@ public static class PickerExtensions
 	{
 		public static void UpdateTitle(this ComboBox nativeComboBox, IPicker picker)
 		{
-			nativeComboBox.Header = string.IsNullOrEmpty(picker.Title) ? null : picker;
-
-			nativeComboBox.HeaderTemplate = string.IsNullOrEmpty(picker.Title) ? null :
-				(UI.Xaml.DataTemplate)UI.Xaml.Application.Current.Resources["ComboBoxHeader"];
+			nativeComboBox.PlaceholderText = picker.Title ?? string.Empty;
+			nativeComboBox.UpdatePlaceholderCharacterSpacing();
+		}
 
+		public static void UpdateTitleColor(this ComboBox nativeComboBox, IPicker picker)
+		{
+			if (picker.TitleColor is null)
+				nativeComboBox.ClearValue(ComboBox.PlaceholderForegroundProperty);
+			else
+				nativeComboBox.PlaceholderForeground = picker.TitleColor.ToPlatform();
 		}
 
 		public static void UpdateBackground(this ComboBox nativeComboBox, IPicker picker)
@@ -75,6 +80,29 @@ public static void UpdateSelectedIndex(this ComboBox nativeComboBox, IPicker pic
 		public static void UpdateCharacterSpacing(this ComboBox nativeComboBox, IPicker picker)
 		{
 			nativeComboBox.CharacterSpacing = picker.CharacterSpacing.ToEm();
+			nativeComboBox.UpdatePlaceholderCharacterSpacing();
+		}
+
+		static void UpdatePlaceholderCharacterSpacing(this ComboBox nativeComboBox)
+		{
+			if (nativeComboBox.IsLoaded)
+			{
+				ApplyPlaceholderCharacterSpacing(nativeComboBox);
+			}
+			else
+			{
+				nativeComboBox.OnLoaded(() => ApplyPlaceholderCharacterSpacing(nativeComboBox));
+			}
+		}
+
+		static void ApplyPlaceholderCharacterSpacing(ComboBox nativeComboBox)
+		{
+			var placeholderTextBlock = nativeComboBox.GetDescendantByName<TextBlock>("PlaceholderTextBlock");
+
+			if (placeholderTextBlock is not null)
+			{
+				placeholderTextBlock.CharacterSpacing = nativeComboBox.CharacterSpacing;
+			}
 		}
 
 		public static void UpdateFont(this ComboBox nativeComboBox, IPicker picker, IFontManager fontManager) =>
@@ -107,4 +135,4 @@ internal static void UpdateIsOpen(this ComboBox nativeComboBox, IPicker picker)
 			nativeComboBox.IsDropDownOpen = picker.IsOpen;
 		}
 	}
-}
+}

src/Core/src/Platform/Windows/Styles/Resources.xaml

@@ -5,7 +5,6 @@
     x:Class="Microsoft.Maui.Platform.Resources">
 
   <ResourceDictionary.MergedDictionaries>
-    <ResourceDictionary Source="MauiComboBoxStyle.xaml" />
     <ResourceDictionary Source="MauiSliderStyle.xaml" />
     <ResourceDictionary Source="MauiStepperStyle.xaml" />
     <ResourceDictionary Source="WindowRootViewStyle.xaml" />

src/Core/src/PublicAPI/net-windows/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
 override Microsoft.Maui.Platform.MauiPasswordTextBox.OnCreateAutomationPeer() -> Microsoft.UI.Xaml.Automation.Peers.AutomationPeer!
+static Microsoft.Maui.Platform.PickerExtensions.UpdateTitleColor(this Microsoft.UI.Xaml.Controls.ComboBox! nativeComboBox, Microsoft.Maui.IPicker! picker) -> void
 static Microsoft.Maui.GridLength.implicit operator Microsoft.Maui.GridLength(string! value) -> Microsoft.Maui.GridLength
 static Microsoft.Maui.SafeAreaEdges.Container.get -> Microsoft.Maui.SafeAreaEdges