chore: Properly display text for selected item

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

@@ -587,14 +587,14 @@ private string TryGetStringValue(object @object/*, PropertyPathListener pathList
 				}
 				else
 				{
-					return spBoxedValue.ToString()!;
+					return FrameworkElement.GetStringFromObject(spBoxedValue);
 					// We've set a BoxedValue, but we can't directly ToString it. Try to get a string out of it.
 				}
 			}
 			else
 			{
 				// If we haven't found a BoxedObject and it's not Stringable, try one last time to get a string out.
-				return @object.ToString()!;
+				return FrameworkElement.GetStringFromObject(@object);
 			}
 		}
 

src/Uno.UI/UI/Xaml/Controls/ComboBox/ComboBox.partial.mux.cs

@@ -310,9 +310,9 @@ private void SetContentPresenter(int index, bool forceSelectionBoxToNull = false
 			}
 		}
 
-		var spGenerator = ItemContainerGenerator;
-		ItemContainerGenerator pItemContainerGenerator = spGenerator;
-		if (m_iLastGeneratedItemIndexforFaceplate > 0)
+		ItemContainerGenerator? spGenerator = null; // TODO Uno: Support for ItemContainerGenerator #17808 (Should reference this.ItemContainerGenerator property)
+		ItemContainerGenerator? pItemContainerGenerator = spGenerator;
+		if (m_iLastGeneratedItemIndexforFaceplate > 0 && pItemContainerGenerator is not null)
 		{
 			// This container was generated just for the purpose of extracting Content and ContentTemplate.
 			// This is the case where we generated an item which was its own container (e.g. defined in XAML or code behind).
@@ -358,7 +358,7 @@ private void SetContentPresenter(int index, bool forceSelectionBoxToNull = false
 		spContainer = ContainerFromIndex(index);
 		spComboBoxItem = spContainer as ComboBoxItem;
 
-		if (spComboBoxItem is null)
+		if (spComboBoxItem is null && pItemContainerGenerator is not null)
 		{
 			bool isNewlyRealized = false;
 			generatorPosition = pItemContainerGenerator.GeneratorPositionFromIndex(index);
@@ -385,6 +385,11 @@ private void SetContentPresenter(int index, bool forceSelectionBoxToNull = false
 			m_iLastGeneratedItemIndexforFaceplate = index;
 		}
 
+		if (spComboBoxItem is null)
+		{
+			return;
+		}
+
 		spContent = spComboBoxItem.Content;
 		{
 			// Because we can't keep UIElement in 2 different place
@@ -421,7 +426,7 @@ private void SetContentPresenter(int index, bool forceSelectionBoxToNull = false
 
 		}
 
-		if (bGeneratedComboBoxItem)
+		if (bGeneratedComboBoxItem && pItemContainerGenerator is not null)
 		{
 			// This container was generated just for the purpose of extracting Content and ContentTemplate
 			// It is not connected to the visual tree which might have unintended consequences, so remove it

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

@@ -1413,4 +1413,14 @@ private void SetUpdateTemplate()
 	}
 
 	partial void SetUpdateTemplatePartial();
+
+	internal string GetTextBlockText()
+	{
+		if (IsUsingDefaultTemplate && ContentTemplateRoot is ImplicitTextBlock tb)
+		{
+			return tb.Text;
+		}
+
+		return null;
+	}
 }

src/Uno.UI/UI/Xaml/Controls/MenuFlyout/MenuFlyoutItem.cs

@@ -742,7 +742,7 @@ protected override AutomationPeer OnCreateAutomationPeer()
 			return new MenuFlyoutItemAutomationPeer(this);
 		}
 
-		private protected override string GetPlainText() => Text;
+		internal override string GetPlainText() => Text;
 
 		internal string KeyboardAcceleratorTextOverrideImpl
 		{

src/Uno.UI/UI/Xaml/Controls/MenuFlyout/MenuFlyoutPresenter.cs

@@ -618,7 +618,7 @@ protected override void OnPointerEntered(PointerRoutedEventArgs pArgs)
 			}
 		}
 
-		private protected override string GetPlainText()
+		internal override string GetPlainText()
 		{
 			string automationName = null;
 

src/Uno.UI/UI/Xaml/Controls/MenuFlyout/MenuFlyoutSubItem.cs

@@ -732,7 +732,7 @@ protected override AutomationPeer OnCreateAutomationPeer()
 			return null;
 		}
 
-		private protected override string GetPlainText() => Text;
+		internal override string GetPlainText() => Text;
 
 		bool ISubMenuOwner.IsSubMenuOpen => IsOpen;
 

src/Uno.UI/UI/Xaml/Controls/Primitives/SelectorItem.partial.mux.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.UI.Xaml.Automation;
+using static Uno.UI.FeatureConfiguration;
+
+namespace Microsoft.UI.Xaml.Controls.Primitives;
+
+partial class SelectorItem
+{
+	//---------------------------------------------------------------------------
+	//
+	//  Synopsis:
+	//      Returns a plain text string to provide a default AutomationProperties.Name
+	//      in the absence of an explicitly defined one
+	//
+	//---------------------------------------------------------------------------
+	internal override string GetPlainText()
+	{
+		string strPlainText = null;
+
+		var contentTemplateRoot = ContentTemplateRoot;
+
+		if (contentTemplateRoot != null)
+		{
+			// we have the first child of the content. Check whether it has an automation name
+
+			strPlainText = AutomationProperties.GetName(contentTemplateRoot);
+
+			// fallback: use getplain text on it
+			if (string.IsNullOrEmpty(strPlainText))
+			{
+				var contentTemplateRootAsIFE = contentTemplateRoot as FrameworkElement;
+
+				strPlainText = null;
+
+				if (contentTemplateRootAsIFE is not null)
+				{
+					strPlainText = contentTemplateRootAsIFE.GetPlainText();
+				}
+			}
+
+			// fallback, use GetPlainText on the contentpresenter, who has some special logic to account for old templates
+			if (string.IsNullOrEmpty(strPlainText))
+			{
+				var contentTemplateRootAsIFE = contentTemplateRoot as FrameworkElement;
+
+				strPlainText = null;
+
+				if (contentTemplateRootAsIFE is not null)
+				{
+					var pParent = contentTemplateRootAsIFE.Parent;
+					if (pParent is ContentPresenter cp)
+					{
+						strPlainText = cp.GetTextBlockText();
+					}
+				}
+			}
+		}
+
+		return strPlainText;
+	}
+}

src/Uno.UI/UI/Xaml/Controls/Slider/Slider.mux.cs

@@ -533,7 +533,7 @@ private void OnPointerCaptureLost(object sender, PointerRoutedEventArgs args)
 	//		in the absence of an explicitly defined one
 	//
 	//---------------------------------------------------------------------------
-	private protected override string GetPlainText()
+	internal override string GetPlainText()
 	{
 		var header = Header;
 

src/Uno.UI/UI/Xaml/FrameworkElement.mux.cs

@@ -10,7 +10,7 @@ namespace Microsoft.UI.Xaml
 {
 	public partial class FrameworkElement
 	{
-		private protected virtual string GetPlainText() => "";
+		internal virtual string GetPlainText() => "";
 
 		internal protected static string GetStringFromObject(object pObject)
 		{