fix: Correctly change PivotHeaderItem content when PivotItem.Header c…

…hanges

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Controls/Given_Pivot.cs

@@ -11,6 +11,7 @@
 using FluentAssertions.Execution;
 using static Private.Infrastructure.TestServices;
 using Uno.UI.Extensions;
+using Windows.UI.Xaml.Controls.Primitives;
 
 namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Controls
 {
@@ -71,6 +72,26 @@ public async Task Check_Binding()
 			items[1].Content.Should().Be(tbs2.ElementAt(0).Text);
 		}
 
+		[TestMethod]
+		[RunsOnUIThread]
+		public async Task Check_Changing_Header_Affects_UI()
+		{
+			var pivotItem = new PivotItem { Header = "Initial text" };
+			var SUT = new Pivot
+			{
+				Items = { pivotItem },
+			};
+
+			WindowHelper.WindowContent = SUT;
+			await WindowHelper.WaitForIdle();
+
+			var pivotHeaderPanel = (PivotHeaderPanel)SUT.GetTemplateChild("StaticHeader");
+			var headerItem = (PivotHeaderItem)pivotHeaderPanel.Children.Single();
+			headerItem.Content.Should().Be("Initial text");
+			pivotItem.Header = "New text";
+			headerItem.Content.Should().Be("New text");
+		}
+
 		private class MyContext
 		{
 			public MyContext()

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

@@ -165,6 +165,7 @@ private void SynchronizeItems()
 
 					if (item is PivotItem pivotItem)
 					{
+						pivotItem.PivotHeaderItem = headerItem;
 						headerItem.Content = pivotItem.Header;
 					}
 					else

src/Uno.UI/UI/Xaml/Controls/Pivot/PivotItem.cs

@@ -3,14 +3,15 @@
 using System.Drawing;
 using System.Text;
 using Uno.UI;
+using Windows.UI.Xaml.Controls.Primitives;
 #if XAMARIN_ANDROID
 using Android.Views;
 #endif
 
 namespace Windows.UI.Xaml.Controls
 {
-    public partial class PivotItem : ContentControl
-    {
+	public partial class PivotItem : ContentControl
+	{
 		public PivotItem()
 		{
 			this.HorizontalAlignment = HorizontalAlignment.Stretch;
@@ -27,6 +28,8 @@ public PivotItem(string header) : this()
 			Header = header;
 		}
 
+		internal PivotHeaderItem PivotHeaderItem { get; set; }
+
 		protected override bool CanCreateTemplateWithoutParent => true;
 
 		public object Header
@@ -35,8 +38,17 @@ public object Header
 			set { this.SetValue(HeaderProperty, value); }
 		}
 
-		public static DependencyProperty HeaderProperty { get ; } =
-			DependencyProperty.Register("Header", typeof(object), typeof(PivotItem), new FrameworkPropertyMetadata(null));
+		public static DependencyProperty HeaderProperty { get; } =
+			DependencyProperty.Register("Header", typeof(object), typeof(PivotItem), new FrameworkPropertyMetadata(null, propertyChangedCallback: OnHeaderChanged));
+
+		private static void OnHeaderChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs args)
+		{
+			if (dependencyObject is PivotItem item && item.PivotHeaderItem != null)
+			{
+				item.PivotHeaderItem.Content = args.NewValue;
+
+			}
+		}
 
 #if XAMARIN_ANDROID
 		// This allows the PivotItem to fill the whole available space.