From 50f76f44e63878a6ba9abfa888f2e9e55362f84d Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Sun, 1 Mar 2026 22:35:51 +1100
Subject: [PATCH 01/10] Add ExpanderAnimationBehavior, IExpansionController,
 ExpandedChangingEventArgs

---
 .../Pages/Views/Expander/ExpanderPage.xaml    | 22 +++++
 .../Pages/Views/Expander/ExpanderPage.xaml.cs | 11 ++-
 ...xpanderAnimationBehaviorDefaults.shared.cs |  9 ++
 .../ExpandedChangingEventArgs.shared.cs       | 17 ++++
 .../ExpanderAnimationBehavior.shared.cs       | 88 ++++++++++++++++++
 .../Interfaces/IExpansionController.shared.cs | 24 +++++
 .../Views/Expander/Expander.shared.cs         | 90 ++++++++++++++++---
 7 files changed, 249 insertions(+), 12 deletions(-)
 create mode 100644 src/CommunityToolkit.Maui.Core/Primitives/Defaults/ExpanderAnimationBehaviorDefaults.shared.cs
 create mode 100644 src/CommunityToolkit.Maui.Core/Primitives/ExpandedChangingEventArgs.shared.cs
 create mode 100644 src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
 create mode 100644 src/CommunityToolkit.Maui/Interfaces/IExpansionController.shared.cs

diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
index d085d031a4..af0bd06ea3 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
@@ -22,6 +22,10 @@
                     <Label Text="Simple Expander (Tap Me)" FontSize="16" FontAttributes="Bold"/>
                 </mct:Expander.Header>
 
+                <mct:Expander.Behaviors>
+                    <mct:ExpanderAnimationBehavior />
+                </mct:Expander.Behaviors>
+
                 <mct:Expander.Content>
                     <VerticalStackLayout>
                         <Label Text="Item 1"/>
@@ -36,11 +40,21 @@
                 <mct:Expander.Header>
                     <Label Text="Multi-Level Expander (Tap Me)" FontSize="16" FontAttributes="Bold"/>
                 </mct:Expander.Header>
+
+                <mct:Expander.Behaviors>
+                    <mct:ExpanderAnimationBehavior />
+                </mct:Expander.Behaviors>
+
                 <mct:Expander.Content>
                     <mct:Expander Direction="Down" BackgroundColor="LightGray">
                         <mct:Expander.Header>
                             <Label Text="Nested Expander (Tap Me)" FontSize="14" FontAttributes="Bold"/>
                         </mct:Expander.Header>
+
+                        <mct:Expander.Behaviors>
+                            <mct:ExpanderAnimationBehavior />
+                        </mct:Expander.Behaviors>
+
                         <mct:Expander.Content>
                             <Label Text="Item 1" />
                         </mct:Expander.Content>
@@ -54,10 +68,16 @@
                 <CollectionView.ItemTemplate>
                     <DataTemplate>
                         <mct:Expander x:DataType="sample:ContentCreator"
+                                      ExpandedChanging="Expander_ExpandedChanging"
                                       ExpandedChanged="Expander_ExpandedChanged">
                             <mct:Expander.Header>
                                 <Label Text="{Binding Name}"/>
                             </mct:Expander.Header>
+
+                            <mct:Expander.Behaviors>
+                                <mct:ExpanderAnimationBehavior />
+                            </mct:Expander.Behaviors>
+
                             <mct:Expander.Content>
                                 <VerticalStackLayout>
                                     <Label Text="{Binding Resource}" HorizontalOptions="Center"/>
@@ -83,6 +103,8 @@
                 <CollectionView.ItemTemplate>
                     <DataTemplate>
                         <mct:Expander x:DataType="sample:ContentCreator"
+                                      HeightRequest="180"
+                                      ExpandedChanging="Expander_ExpandedChanging"
                                       ExpandedChanged="Expander_ExpandedChanged">
                             <mct:Expander.Header>
                                 <Label Text="{Binding Name}"/>
diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
index 9747bdc246..a214ef50f9 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
@@ -1,4 +1,5 @@
 using System.Diagnostics.CodeAnalysis;
+using System.Diagnostics;
 using CommunityToolkit.Maui.Alerts;
 using CommunityToolkit.Maui.Sample.ViewModels.Views;
 
@@ -11,10 +12,18 @@ public ExpanderPage(ExpanderViewModel viewModel) : base(viewModel)
 		InitializeComponent();
 	}
 
+	Stopwatch stopWatch = new();
+
+	void Expander_ExpandedChanging(object? sender, Core.ExpandedChangingEventArgs e)
+	{
+		stopWatch.Restart();
+	}
+
 	async void Expander_ExpandedChanged(object? sender, Core.ExpandedChangedEventArgs e)
 	{
+		stopWatch.Stop();
 		var collapsedText = e.IsExpanded ? "expanded" : "collapsed";
-		await Toast.Make($"Expander is {collapsedText}").Show(CancellationToken.None);
+		await Toast.Make($"Expander is {collapsedText} ({stopWatch.ElapsedMilliseconds} ms)").Show(CancellationToken.None);
 	}
 
 	async void GoToCSharpSampleClicked(object? sender, EventArgs? e)
diff --git a/src/CommunityToolkit.Maui.Core/Primitives/Defaults/ExpanderAnimationBehaviorDefaults.shared.cs b/src/CommunityToolkit.Maui.Core/Primitives/Defaults/ExpanderAnimationBehaviorDefaults.shared.cs
new file mode 100644
index 0000000000..4adf94fabc
--- /dev/null
+++ b/src/CommunityToolkit.Maui.Core/Primitives/Defaults/ExpanderAnimationBehaviorDefaults.shared.cs
@@ -0,0 +1,9 @@
+namespace CommunityToolkit.Maui.Core;
+
+static class ExpanderAnimationBehaviorDefaults
+{
+	public const uint CollapsingLength = 250u;
+	public static Easing CollapsingEasing { get; } = Easing.Linear;
+	public const uint ExpandingLength = 250u;
+	public static Easing ExpandingEasing { get; } = Easing.Linear;
+}
diff --git a/src/CommunityToolkit.Maui.Core/Primitives/ExpandedChangingEventArgs.shared.cs b/src/CommunityToolkit.Maui.Core/Primitives/ExpandedChangingEventArgs.shared.cs
new file mode 100644
index 0000000000..e97f18a66a
--- /dev/null
+++ b/src/CommunityToolkit.Maui.Core/Primitives/ExpandedChangingEventArgs.shared.cs
@@ -0,0 +1,17 @@
+namespace CommunityToolkit.Maui.Core;
+
+/// <summary>
+/// Provides data for an event that occurs when an Expander is about to change its IsExpanded state.
+/// </summary>
+public class ExpandedChangingEventArgs(bool oldIsExpanded, bool newIsExpanded) : EventArgs
+{
+	/// <summary>
+	/// True if expander was expanded before the change.
+	/// </summary>
+	public bool OldIsExpanded { get; } = oldIsExpanded;
+
+	/// <summary>
+	/// True if expander will be expanded after the change.
+	/// </summary>
+	public bool NewIsExpanded { get; } = newIsExpanded;
+}
diff --git a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
new file mode 100644
index 0000000000..446bf7fabe
--- /dev/null
+++ b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
@@ -0,0 +1,88 @@
+using CommunityToolkit.Maui.Core;
+using CommunityToolkit.Maui.Views;
+
+namespace CommunityToolkit.Maui.Behaviors;
+
+/// <summary>
+/// A behavior that adds smooth expand and collapse animations to an <see cref="Views.Expander"/>.
+/// </summary>
+public partial class ExpanderAnimationBehavior : BaseBehavior<Views.Expander>, IExpansionController
+{
+	/// <summary>
+	/// Gets or sets the easing function used when the expander collapses.
+	/// </summary>
+	[BindableProperty]
+	public partial Easing CollapsingEasing { get; set; } = ExpanderAnimationBehaviorDefaults.CollapsingEasing;
+
+	/// <summary>
+	/// Gets or sets the duration, in milliseconds, of the collapse animation.
+	/// </summary>
+	[BindableProperty]
+	public partial uint CollapsingLength { get; set; } = ExpanderAnimationBehaviorDefaults.CollapsingLength;
+
+	/// <summary>
+	/// Gets or sets the easing function used when the expander expands.
+	/// </summary>
+	[BindableProperty]
+	public partial Easing ExpandingEasing { get; set; } = ExpanderAnimationBehaviorDefaults.ExpandingEasing;
+
+	/// <summary>
+	/// Gets or sets the duration, in milliseconds, of the expansion animation.
+	/// </summary>
+	[BindableProperty]
+	public partial uint ExpandingLength { get; set; } = ExpanderAnimationBehaviorDefaults.ExpandingLength;
+
+	/// <summary>
+	/// Attaches the behavior to the specified expander and assigns it as the controller responsible for handling expansion animations.
+	/// </summary>
+	/// <param name="bindable">The Expander control to which the behavior is being attached to.</param>
+	protected override void OnAttachedTo(Views.Expander bindable)
+	{
+		base.OnAttachedTo(bindable);
+		bindable.ExpansionController = this;
+	}
+
+	/// <summary>
+	/// Detaches the behavior from the specified Expander control and resets its expansion controller to the shared instance.
+	/// </summary>
+	/// <param name="bindable">The Expander control from which the behavior is being detached from.</param>
+	protected override void OnDetachingFrom(Views.Expander bindable)
+	{
+		base.OnDetachingFrom(bindable);
+		bindable.ExpansionController = InstantExpansionController.Instance;
+	}
+
+	/// <summary>
+	/// Performs the animation that runs when the expander transitions from a collapsed to an expanded state.
+	/// </summary>
+	/// <param name="expander">The Expander control that is expanding.</param>
+	public async Task OnExpandingAsync(Views.Expander expander)
+	{
+		if (expander.ContentHost is ContentView host && expander.Content is View view)
+		{
+			var tcs = new TaskCompletionSource();
+			var size = view.Measure(host.Width, double.PositiveInfinity);
+			var animation = new Animation(v => host.HeightRequest = v, 0, size.Height);
+			animation.Commit(expander, "ExpandingAnimation", 16, ExpandingLength, ExpandingEasing, (v, c) => tcs.TrySetResult());
+			host.HeightRequest = -1;
+			await tcs.Task;
+		}
+	}
+
+	/// <summary>
+	/// Performs the animation that runs when the expander transitions from an expanded to a collapsed state.
+	/// </summary>
+	/// <param name="expander">The Expander control that is collapsing.</param>
+	public async Task OnCollapsingAsync(Views.Expander expander)
+	{
+		if (expander.ContentHost is ContentView host && expander.Content is View view)
+		{
+			var tcs = new TaskCompletionSource();
+			var size = view.Measure(host.Width, double.PositiveInfinity);
+			var animation = new Animation(v => host.HeightRequest = v, size.Height, 0);
+			animation.Commit(expander, "CollapsingAnimation", 16, CollapsingLength, CollapsingEasing, (v, c) => tcs.TrySetResult());
+			host.HeightRequest = 0;
+			await tcs.Task;
+		}
+	}
+}
diff --git a/src/CommunityToolkit.Maui/Interfaces/IExpansionController.shared.cs b/src/CommunityToolkit.Maui/Interfaces/IExpansionController.shared.cs
new file mode 100644
index 0000000000..01d1f2a696
--- /dev/null
+++ b/src/CommunityToolkit.Maui/Interfaces/IExpansionController.shared.cs
@@ -0,0 +1,24 @@
+namespace CommunityToolkit.Maui;
+
+/// <summary>
+/// Defines a pluggable controller responsible for handling expansion
+/// and collapse transitions for an <see cref="Views.Expander"/>.
+/// </summary>
+public interface IExpansionController
+{
+	/// <summary>
+	/// Executes asynchronous logic when the expander transitions
+	/// from a collapsed to an expanded state.
+	/// </summary>
+	/// <param name="expander">The <see cref="Views.Expander"/> instance initiating the expansion.</param>
+	/// <returns>A task representing the asynchronous operation.</returns>
+	Task OnExpandingAsync(Views.Expander expander);
+
+	/// <summary>
+	/// Executes asynchronous logic when the expander transitions
+	/// from an expanded to a collapsed state.
+	/// </summary>
+	/// <param name="expander">The <see cref="Views.Expander"/> instance initiating the collapse.</param>
+	/// <returns>A task representing the asynchronous operation.</returns>
+	Task OnCollapsingAsync(Views.Expander expander);
+}
diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index ed1f67f9c5..d15183b220 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -10,7 +10,8 @@ namespace CommunityToolkit.Maui.Views;
 [RequiresUnreferencedCode("Calls Microsoft.Maui.Controls.Binding.Binding(String, BindingMode, IValueConverter, Object, String, Object)")]
 public partial class Expander : ContentView, IExpander
 {
-	readonly WeakEventManager tappedEventManager = new();
+	readonly WeakEventManager expandedChangingEventManager = new();
+	readonly WeakEventManager expandedChangedEventManager = new();
 
 	/// <summary>
 	/// Initialize a new instance of <see cref="Expander"/>.
@@ -30,13 +31,22 @@ public Expander()
 		};
 	}
 
+	/// <summary>
+	/// Triggered when the expander is about to change
+	/// </summary>
+	public event EventHandler<ExpandedChangingEventArgs> ExpandedChanging
+	{
+		add => expandedChangingEventManager.AddEventHandler(value);
+		remove => expandedChangingEventManager.RemoveEventHandler(value);
+	}
+
 	/// <summary>
 	/// Triggered when the value of <see cref="IsExpanded"/> changes.
 	/// </summary>
 	public event EventHandler<ExpandedChangedEventArgs> ExpandedChanged
 	{
-		add => tappedEventManager.AddEventHandler(value);
-		remove => tappedEventManager.RemoveEventHandler(value);
+		add => expandedChangedEventManager.AddEventHandler(value);
+		remove => expandedChangedEventManager.RemoveEventHandler(value);
 	}
 
 	/// <summary>
@@ -75,6 +85,13 @@ public event EventHandler<ExpandedChangedEventArgs> ExpandedChanged
 	[BindableProperty(PropertyChangedMethodName = nameof(OnHeaderPropertyChanged))]
 	public partial IView Header { get; set; }
 
+	/// <summary>
+	/// Gets or sets the component that performs the expansion and collapse
+	/// logic for this expander, including any optional animations.
+	/// </summary>
+	[BindableProperty]
+	public partial IExpansionController ExpansionController { get; set; } = InstantExpansionController.Instance;
+
 	/// <summary>
 	/// The Action that fires when <see cref="Header"/> is tapped.
 	/// By default, this <see cref="Action"/> runs <see cref="ResizeExpanderInItemsView(TappedEventArgs)"/>.
@@ -88,6 +105,12 @@ public event EventHandler<ExpandedChangedEventArgs> ExpandedChanged
 
 	Grid ContentGrid => (Grid)base.Content;
 
+	/// <summary>
+	/// Gets the <see cref="ContentView"/> that hosts the expander's content,
+	/// which can be used to apply animation or transition effects during expansion and collapse.
+	/// </summary>
+	public ContentView? ContentHost { get; internal set; }
+
 	static void OnExpandDirectionChanging(BindableObject bindable, object oldValue, object newValue)
 	{
 		var direction = (Expander)bindable;
@@ -104,11 +127,13 @@ static void OnContentPropertyChanged(BindableObject bindable, object oldValue, o
 		var expander = (Expander)bindable;
 		if (newValue is View view)
 		{
-			view.SetBinding(IsVisibleProperty, new Binding(nameof(IsExpanded), source: expander));
-
-			expander.ContentGrid.Remove(oldValue);
-			expander.ContentGrid.Add(newValue);
-			expander.ContentGrid.SetRow(view, expander.Direction switch
+			if (expander.ContentHost is not null)
+			{
+				expander.ContentGrid.Remove(expander.ContentHost);
+			}
+			expander.ContentHost = new ContentView { Content = view, IsClippedToBounds = true, HeightRequest = 0 };
+			expander.ContentGrid.Add(expander.ContentHost);
+			expander.ContentGrid.SetRow(expander.ContentHost, expander.Direction switch
 			{
 				ExpandDirection.Down => 1,
 				ExpandDirection.Up => 0,
@@ -181,7 +206,19 @@ void OnHeaderTapGestureRecognizerTapped(object? sender, TappedEventArgs tappedEv
 		HandleHeaderTapped?.Invoke(tappedEventArgs);
 	}
 
+	TaskCompletionSource resizeTCS = new();
+
 	void ResizeExpanderInItemsView(TappedEventArgs tappedEventArgs)
+	{
+		_ = Dispatcher.Dispatch(async () =>
+		{
+			resizeTCS = new();
+			await resizeTCS.Task;
+			ResizeExpanderInItemsView2(tappedEventArgs);
+		});
+	}
+
+	void ResizeExpanderInItemsView2(TappedEventArgs tappedEventArgs)
 	{
 		if (Header is null)
 		{
@@ -211,7 +248,6 @@ void ResizeExpanderInItemsView(TappedEventArgs tappedEventArgs)
 			else if (element is CollectionView collectionView)
 			{
 				var tapLocation = tappedEventArgs.GetPosition(collectionView);
-				ForceUpdateCellSize(collectionView, size, tapLocation);
 			}
 #endif
 
@@ -221,11 +257,43 @@ void ResizeExpanderInItemsView(TappedEventArgs tappedEventArgs)
 
 	void IExpander.ExpandedChanged(bool isExpanded)
 	{
+		_ = Dispatcher.Dispatch(async () => await ExpandedChangedAsync(!isExpanded, isExpanded));
+	}
+
+	async Task ExpandedChangedAsync(bool wasExpanded, bool isExpanded)
+	{
+		expandedChangingEventManager.HandleEvent(this, new ExpandedChangingEventArgs(wasExpanded, isExpanded), nameof(ExpandedChanging));
+
+		if (ContentHost is ContentView host && Content is View view)
+		{
+			if (!wasExpanded && isExpanded)
+			{
+				view.IsVisible = true;
+				await ExpansionController.OnExpandingAsync(this);
+				host.HeightRequest = -1;
+			}
+			else
+			{
+				await ExpansionController.OnCollapsingAsync(this);
+				host.HeightRequest = 0;
+				view.IsVisible = false;
+			}
+		}
+
+		resizeTCS.TrySetResult();
+
 		if (Command?.CanExecute(CommandParameter) is true)
 		{
 			Command.Execute(CommandParameter);
 		}
 
-		tappedEventManager.HandleEvent(this, new ExpandedChangedEventArgs(isExpanded), nameof(ExpandedChanged));
+		expandedChangedEventManager.HandleEvent(this, new ExpandedChangedEventArgs(isExpanded), nameof(ExpandedChanged));
 	}
-}
\ No newline at end of file
+}
+
+class InstantExpansionController : IExpansionController
+{
+	public static InstantExpansionController Instance { get; } = new();
+	public Task OnExpandingAsync(Expander expander) => Task.CompletedTask;
+	public Task OnCollapsingAsync(Expander expander) => Task.CompletedTask;
+}

From b828c279c879dc7aef315268b233498a6dfe9b8c Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 07:50:59 +1100
Subject: [PATCH 02/10] Implemented Copilot feedback

---
 .../ExpanderAnimationBehavior.shared.cs       | 19 ++++-------------
 .../Views/Expander/Expander.shared.cs         | 21 ++++++++++++-------
 2 files changed, 17 insertions(+), 23 deletions(-)

diff --git a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
index 446bf7fabe..31f1cc2ab5 100644
--- a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
+++ b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
@@ -1,5 +1,4 @@
 using CommunityToolkit.Maui.Core;
-using CommunityToolkit.Maui.Views;
 
 namespace CommunityToolkit.Maui.Behaviors;
 
@@ -42,16 +41,6 @@ protected override void OnAttachedTo(Views.Expander bindable)
 		bindable.ExpansionController = this;
 	}
 
-	/// <summary>
-	/// Detaches the behavior from the specified Expander control and resets its expansion controller to the shared instance.
-	/// </summary>
-	/// <param name="bindable">The Expander control from which the behavior is being detached from.</param>
-	protected override void OnDetachingFrom(Views.Expander bindable)
-	{
-		base.OnDetachingFrom(bindable);
-		bindable.ExpansionController = InstantExpansionController.Instance;
-	}
-
 	/// <summary>
 	/// Performs the animation that runs when the expander transitions from a collapsed to an expanded state.
 	/// </summary>
@@ -63,8 +52,8 @@ public async Task OnExpandingAsync(Views.Expander expander)
 			var tcs = new TaskCompletionSource();
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, 0, size.Height);
-			animation.Commit(expander, "ExpandingAnimation", 16, ExpandingLength, ExpandingEasing, (v, c) => tcs.TrySetResult());
-			host.HeightRequest = -1;
+			animation.Commit(expander, "ExpanderAnimation", 16, ExpandingLength, ExpandingEasing,
+				(v, c) => { tcs.TrySetResult(); host.HeightRequest = -1; });
 			await tcs.Task;
 		}
 	}
@@ -80,8 +69,8 @@ public async Task OnCollapsingAsync(Views.Expander expander)
 			var tcs = new TaskCompletionSource();
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, size.Height, 0);
-			animation.Commit(expander, "CollapsingAnimation", 16, CollapsingLength, CollapsingEasing, (v, c) => tcs.TrySetResult());
-			host.HeightRequest = 0;
+			animation.Commit(expander, "ExpanderAnimation", 16, CollapsingLength, CollapsingEasing,
+				(v, c) => { tcs.TrySetResult(); host.HeightRequest = 0; });
 			await tcs.Task;
 		}
 	}
diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index d15183b220..ad284ef810 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -131,7 +131,16 @@ static void OnContentPropertyChanged(BindableObject bindable, object oldValue, o
 			{
 				expander.ContentGrid.Remove(expander.ContentHost);
 			}
-			expander.ContentHost = new ContentView { Content = view, IsClippedToBounds = true, HeightRequest = 0 };
+
+			// Initialize content visibility and height based on the current expansion state
+			view.IsVisible = expander.IsExpanded;
+			expander.ContentHost = new ContentView
+			{
+				Content = view,
+				IsClippedToBounds = true,
+				HeightRequest = expander.IsExpanded ? -1 : 0
+			};
+
 			expander.ContentGrid.Add(expander.ContentHost);
 			expander.ContentGrid.SetRow(expander.ContentHost, expander.Direction switch
 			{
@@ -171,7 +180,7 @@ static void OnDirectionPropertyChanged(BindableObject bindable, object oldValue,
 
 	void HandleDirectionChanged(ExpandDirection expandDirection)
 	{
-		if (Header is null || Content is null)
+		if (Header is null || ContentHost is null)
 		{
 			return;
 		}
@@ -180,12 +189,12 @@ void HandleDirectionChanged(ExpandDirection expandDirection)
 		{
 			case ExpandDirection.Down:
 				ContentGrid.SetRow(Header, 0);
-				ContentGrid.SetRow(Content, 1);
+				ContentGrid.SetRow(ContentHost, 1);
 				break;
 
 			case ExpandDirection.Up:
 				ContentGrid.SetRow(Header, 1);
-				ContentGrid.SetRow(Content, 0);
+				ContentGrid.SetRow(ContentHost, 0);
 				break;
 
 			default:
@@ -245,10 +254,6 @@ void ResizeExpanderInItemsView2(TappedEventArgs tappedEventArgs)
 			{
 				cell.ForceUpdateSize();
 			}
-			else if (element is CollectionView collectionView)
-			{
-				var tapLocation = tappedEventArgs.GetPosition(collectionView);
-			}
 #endif
 
 			element = element.Parent;

From acdc9e279bffb1e2e62586b653362c0894b2760b Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 11:28:58 +1100
Subject: [PATCH 03/10] Add new unit tests ExpanderController, Expanding and
 ExpanderAnimationBehavior

---
 .../Views/Expander/ExpanderTests.cs           | 145 ++++++++++++++++++
 1 file changed, 145 insertions(+)

diff --git a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
index 30b18fadb0..8072187557 100644
--- a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
+++ b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
@@ -1,5 +1,8 @@
 using System.ComponentModel;
+using System.Text;
+using CommunityToolkit.Maui.Behaviors;
 using CommunityToolkit.Maui.Core;
+using CommunityToolkit.Maui.Views;
 using FluentAssertions;
 using Xunit;
 
@@ -117,4 +120,146 @@ public void EnsureDefaults()
 		var expander = new Maui.Views.Expander();
 		Assert.Equal(ExpanderDefaults.Direction, expander.Direction);
 	}
+
+	[Fact]
+	public async Task ExpanderRaisesEventsInCorrectOrderWhenExpanding()
+	{
+		TaskCompletionSource tcs = new();
+		var expander = new Maui.Views.Expander();
+		StringBuilder callOrder = new();
+		expander.ExpandedChanging += (_, _) => callOrder.Append("changing,");
+		expander.ExpandedChanged += (_, _) => { callOrder.Append("changed,"); tcs.TrySetResult(); };
+		var controller = new MockExpansionController();
+		controller.Expanding += (_, _) => callOrder.Append("controllerExpanding,");
+		controller.Collapsing += (_, _) => callOrder.Append("controllerCollapsing,");
+		expander.ExpansionController = controller;
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		expander.IsExpanded = true;
+		await tcs.Task;
+		Assert.Equal("changing,controllerExpanding,changed,", callOrder.ToString());
+	}
+
+	[Fact]
+	public async Task ExpanderCallsCorrectControllerMethod()
+	{
+		TaskCompletionSource tcs = new();
+		var expander = new Maui.Views.Expander();
+		expander.ExpandedChanged += (_, _) => tcs.TrySetResult();
+		var controller = new MockExpansionController();
+		expander.ExpansionController = controller;
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		expander.IsExpanded = true;
+		await tcs.Task;
+		Assert.Equal(1, controller.ExpandingCount);
+		Assert.Equal(0, controller.CollapsingCount);
+	}
+
+	[Fact]
+	public async Task ExpanderExpandsContentBecomesVisibleHeightRestored()
+	{
+		var tcs = new TaskCompletionSource();
+		var expander = new Maui.Views.Expander();
+		expander.ExpandedChanged += (_, _) => tcs.TrySetResult();
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		expander.IsExpanded = true;
+		await tcs.Task;
+		var element = expander.Content as VisualElement;
+		Assert.NotNull(expander.ContentHost);
+		Assert.NotNull(expander.Content);
+		Assert.NotNull(element);
+		Assert.True(element.IsVisible);
+		Assert.Equal(-1, expander.ContentHost.HeightRequest);
+	}
+
+	[Fact]
+	public async Task ExpanderCollapseContentHiddenHeightZero()
+	{
+		var expander = new Maui.Views.Expander();
+		expander.IsExpanded = true;
+		var tcs = new TaskCompletionSource();
+		expander.ExpandedChanged += (_, _) => tcs.TrySetResult();
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		expander.IsExpanded = false;
+		await tcs.Task;
+		var element = expander.Content as VisualElement;
+		Assert.NotNull(expander.ContentHost);
+		Assert.NotNull(expander.Content);
+		Assert.NotNull(element);
+		Assert.False(element.IsVisible);
+		Assert.Equal(0, expander.ContentHost.HeightRequest);
+	}
+
+	[Fact]
+	public async Task ExpanderIsExpandedSetBeforeContentAssignedInitialStateCorrect()
+	{
+		var expander = new Maui.Views.Expander();
+		expander.IsExpanded = true;
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		var element = expander.Content as VisualElement;
+		Assert.NotNull(expander.ContentHost);
+		Assert.NotNull(element);
+		Assert.True(element.IsVisible);
+		Assert.Equal(-1, expander.ContentHost.HeightRequest);
+	}
+
+	[Fact]
+	public async Task AttachingAnimationBehaviorSetsExpansionController()
+	{
+		var expander = new Maui.Views.Expander();
+		var behavior = new ExpanderAnimationBehavior();
+		expander.Behaviors.Add(behavior);
+		Assert.IsType<ExpanderAnimationBehavior>(expander.Behaviors[0]);
+		Assert.IsType<ExpanderAnimationBehavior>(behavior);
+		Assert.IsType<ExpanderAnimationBehavior>(expander.ExpansionController);
+		Assert.Same(behavior, expander.ExpansionController);
+	}
+
+	[Fact]
+	public async Task OnExpandingAsyncAnimatesHeightCorrectly()
+	{
+		var tcs = new TaskCompletionSource();
+		var expander = new Maui.Views.Expander();
+		expander.ExpandedChanged += (_, _) => tcs.TrySetResult();
+		var behavior = new ExpanderAnimationBehavior();
+		expander.Behaviors.Add(behavior);
+		expander.Header = new Label { Text = "Header" };
+		expander.Content = new Label { Text = "Hello" };
+		Assert.NotNull(expander.ContentHost);
+		expander.ContentHost.HeightRequest = 0;
+		expander.IsExpanded = true;
+		await tcs.Task;
+		var element = expander.Content as VisualElement;
+		Assert.True(expander.IsExpanded);
+		Assert.Equal(-1, expander.ContentHost.HeightRequest);
+		Assert.NotNull(element);
+		Assert.True(element.IsVisible);
+	}
+
+	class MockExpansionController : IExpansionController
+	{
+		public event EventHandler? Expanding;
+		public event EventHandler? Collapsing;
+
+		public int ExpandingCount { get; private set; } = 0;
+		public int CollapsingCount { get; private set; } = 0;
+
+		public async Task OnExpandingAsync(Expander expander)
+		{
+			await Task.Yield();
+			ExpandingCount++;
+			Expanding?.Invoke(this, EventArgs.Empty);
+		}
+
+		public async Task OnCollapsingAsync(Expander expander)
+		{
+			await Task.Yield();
+			CollapsingCount++;
+			Collapsing?.Invoke(this, EventArgs.Empty);
+		}
+	}
 }
\ No newline at end of file

From 18803ea5a6ce7e1188edddd2339649de08a148b3 Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 13:12:59 +1100
Subject: [PATCH 04/10] Implement unit tests changes as well as TCS gate as
 recommended by Copilot

---
 .../Pages/Views/Expander/ExpanderPage.xaml    |  1 -
 .../Pages/Views/Expander/ExpanderPage.xaml.cs | 23 +++++++--
 .../Views/Expander/ExpanderTests.cs           | 14 +++---
 .../ExpanderAnimationBehavior.shared.cs       | 17 +++++++
 .../Views/Expander/Expander.shared.cs         | 47 ++++++++++++-------
 5 files changed, 73 insertions(+), 29 deletions(-)

diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
index af0bd06ea3..f102c8b15d 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
@@ -104,7 +104,6 @@
                     <DataTemplate>
                         <mct:Expander x:DataType="sample:ContentCreator"
                                       HeightRequest="180"
-                                      ExpandedChanging="Expander_ExpandedChanging"
                                       ExpandedChanged="Expander_ExpandedChanged">
                             <mct:Expander.Header>
                                 <Label Text="{Binding Name}"/>
diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
index a214ef50f9..984583d14d 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
@@ -1,7 +1,7 @@
 using System.Diagnostics.CodeAnalysis;
-using System.Diagnostics;
 using CommunityToolkit.Maui.Alerts;
 using CommunityToolkit.Maui.Sample.ViewModels.Views;
+using CommunityToolkit.Maui.Views;
 
 namespace CommunityToolkit.Maui.Sample.Pages.Views;
 
@@ -12,18 +12,31 @@ public ExpanderPage(ExpanderViewModel viewModel) : base(viewModel)
 		InitializeComponent();
 	}
 
-	Stopwatch stopWatch = new();
+	Dictionary<Expander, long> expandTimes = new();
 
 	void Expander_ExpandedChanging(object? sender, Core.ExpandedChangingEventArgs e)
 	{
-		stopWatch.Restart();
+		if (sender is Expander expander)
+		{
+			expandTimes[expander] = DateTime.Now.Ticks;
+		}
 	}
 
 	async void Expander_ExpandedChanged(object? sender, Core.ExpandedChangedEventArgs e)
 	{
-		stopWatch.Stop();
 		var collapsedText = e.IsExpanded ? "expanded" : "collapsed";
-		await Toast.Make($"Expander is {collapsedText} ({stopWatch.ElapsedMilliseconds} ms)").Show(CancellationToken.None);
+		if (sender is Expander expander)
+		{
+			if (expandTimes.TryGetValue(expander, out var startTime))
+			{
+				var elapsed = DateTime.Now.Ticks - startTime;
+				await Toast.Make($"Expander is {collapsedText} ({elapsed} ms)").Show(CancellationToken.None);
+			}
+			else
+			{
+				await Toast.Make($"Expander is {collapsedText}").Show(CancellationToken.None);
+			}
+		}
 	}
 
 	async void GoToCSharpSampleClicked(object? sender, EventArgs? e)
diff --git a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
index 8072187557..196aafea80 100644
--- a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
+++ b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
@@ -121,7 +121,7 @@ public void EnsureDefaults()
 		Assert.Equal(ExpanderDefaults.Direction, expander.Direction);
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task ExpanderRaisesEventsInCorrectOrderWhenExpanding()
 	{
 		TaskCompletionSource tcs = new();
@@ -140,7 +140,7 @@ public async Task ExpanderRaisesEventsInCorrectOrderWhenExpanding()
 		Assert.Equal("changing,controllerExpanding,changed,", callOrder.ToString());
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task ExpanderCallsCorrectControllerMethod()
 	{
 		TaskCompletionSource tcs = new();
@@ -156,7 +156,7 @@ public async Task ExpanderCallsCorrectControllerMethod()
 		Assert.Equal(0, controller.CollapsingCount);
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task ExpanderExpandsContentBecomesVisibleHeightRestored()
 	{
 		var tcs = new TaskCompletionSource();
@@ -174,7 +174,7 @@ public async Task ExpanderExpandsContentBecomesVisibleHeightRestored()
 		Assert.Equal(-1, expander.ContentHost.HeightRequest);
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task ExpanderCollapseContentHiddenHeightZero()
 	{
 		var expander = new Maui.Views.Expander();
@@ -193,7 +193,7 @@ public async Task ExpanderCollapseContentHiddenHeightZero()
 		Assert.Equal(0, expander.ContentHost.HeightRequest);
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task ExpanderIsExpandedSetBeforeContentAssignedInitialStateCorrect()
 	{
 		var expander = new Maui.Views.Expander();
@@ -208,7 +208,7 @@ public async Task ExpanderIsExpandedSetBeforeContentAssignedInitialStateCorrect(
 	}
 
 	[Fact]
-	public async Task AttachingAnimationBehaviorSetsExpansionController()
+	public void AttachingAnimationBehaviorSetsExpansionController()
 	{
 		var expander = new Maui.Views.Expander();
 		var behavior = new ExpanderAnimationBehavior();
@@ -219,7 +219,7 @@ public async Task AttachingAnimationBehaviorSetsExpansionController()
 		Assert.Same(behavior, expander.ExpansionController);
 	}
 
-	[Fact]
+	[Fact(Timeout = (int)TestDuration.Short)]
 	public async Task OnExpandingAsyncAnimatesHeightCorrectly()
 	{
 		var tcs = new TaskCompletionSource();
diff --git a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
index 31f1cc2ab5..4dc5a22b39 100644
--- a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
+++ b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
@@ -1,4 +1,5 @@
 using CommunityToolkit.Maui.Core;
+using CommunityToolkit.Maui.Views;
 
 namespace CommunityToolkit.Maui.Behaviors;
 
@@ -31,6 +32,8 @@ public partial class ExpanderAnimationBehavior : BaseBehavior<Views.Expander>, I
 	[BindableProperty]
 	public partial uint ExpandingLength { get; set; } = ExpanderAnimationBehaviorDefaults.ExpandingLength;
 
+	IExpansionController previousController = InstantExpansionController.Instance;
+
 	/// <summary>
 	/// Attaches the behavior to the specified expander and assigns it as the controller responsible for handling expansion animations.
 	/// </summary>
@@ -38,9 +41,23 @@ public partial class ExpanderAnimationBehavior : BaseBehavior<Views.Expander>, I
 	protected override void OnAttachedTo(Views.Expander bindable)
 	{
 		base.OnAttachedTo(bindable);
+		previousController = bindable.ExpansionController ?? InstantExpansionController.Instance;
 		bindable.ExpansionController = this;
 	}
 
+	/// <summary>
+	/// Detaches the behavior from the specified Expander control and restores its previous expansion controller.
+	/// </summary>
+	/// <param name="bindable">The Expander control from which the behavior is being detached.</param>
+	protected override void OnDetachingFrom(Views.Expander bindable)
+	{
+		base.OnDetachingFrom(bindable);
+		if (bindable.ExpansionController == this)
+		{
+			bindable.ExpansionController = previousController;
+		}
+	}
+
 	/// <summary>
 	/// Performs the animation that runs when the expander transitions from a collapsed to an expanded state.
 	/// </summary>
diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index ad284ef810..72520e3db0 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -215,14 +215,24 @@ void OnHeaderTapGestureRecognizerTapped(object? sender, TappedEventArgs tappedEv
 		HandleHeaderTapped?.Invoke(tappedEventArgs);
 	}
 
-	TaskCompletionSource resizeTCS = new();
+	TaskCompletionSource expansionGate = new();
+
+	Task WaitForExpandedChangedAsync()
+	{
+		if (!expansionGate.Task.IsCompleted)
+		{
+			return expansionGate.Task;
+		}
+
+		expansionGate = new(TaskCreationOptions.RunContinuationsAsynchronously);
+		return expansionGate.Task;
+	}
 
 	void ResizeExpanderInItemsView(TappedEventArgs tappedEventArgs)
 	{
 		_ = Dispatcher.Dispatch(async () =>
 		{
-			resizeTCS = new();
-			await resizeTCS.Task;
+			await WaitForExpandedChangedAsync();
 			ResizeExpanderInItemsView2(tappedEventArgs);
 		});
 	}
@@ -269,23 +279,28 @@ async Task ExpandedChangedAsync(bool wasExpanded, bool isExpanded)
 	{
 		expandedChangingEventManager.HandleEvent(this, new ExpandedChangingEventArgs(wasExpanded, isExpanded), nameof(ExpandedChanging));
 
-		if (ContentHost is ContentView host && Content is View view)
+		try
 		{
-			if (!wasExpanded && isExpanded)
+			if (ContentHost is ContentView host && Content is View view)
 			{
-				view.IsVisible = true;
-				await ExpansionController.OnExpandingAsync(this);
-				host.HeightRequest = -1;
-			}
-			else
-			{
-				await ExpansionController.OnCollapsingAsync(this);
-				host.HeightRequest = 0;
-				view.IsVisible = false;
+				if (!wasExpanded && isExpanded)
+				{
+					view.IsVisible = true;
+					await ExpansionController.OnExpandingAsync(this);
+					host.HeightRequest = -1;
+				}
+				else
+				{
+					await ExpansionController.OnCollapsingAsync(this);
+					host.HeightRequest = 0;
+					view.IsVisible = false;
+				}
 			}
 		}
-
-		resizeTCS.TrySetResult();
+		finally
+		{
+			expansionGate.TrySetResult();
+		}
 
 		if (Command?.CanExecute(CommandParameter) is true)
 		{

From 71888e6d63f4ecf8921918d49b90991f81c8c7fc Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 15:29:20 +1100
Subject: [PATCH 05/10] Make InstantExpansionController a sealed singleton with
 private constructor

---
 src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index 72520e3db0..4aa0b88900 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -311,9 +311,10 @@ async Task ExpandedChangedAsync(bool wasExpanded, bool isExpanded)
 	}
 }
 
-class InstantExpansionController : IExpansionController
+sealed class InstantExpansionController : IExpansionController
 {
 	public static InstantExpansionController Instance { get; } = new();
+	InstantExpansionController() { }
 	public Task OnExpandingAsync(Expander expander) => Task.CompletedTask;
 	public Task OnCollapsingAsync(Expander expander) => Task.CompletedTask;
 }

From 4186bbd0a93ec3edf9cad01d3f6a7b218abe792b Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 20:04:39 +1100
Subject: [PATCH 06/10] Reverted ExpanderPage. Made
 Expander.ExpansionController nullable.

---
 .../Pages/Views/Expander/ExpanderPage.xaml    |  1 -
 .../Pages/Views/Expander/ExpanderPage.xaml.cs | 24 +------------------
 .../ExpanderAnimationBehavior.shared.cs       |  9 ++++---
 .../Views/Expander/Expander.shared.cs         | 17 ++++++++-----
 4 files changed, 16 insertions(+), 35 deletions(-)

diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
index f102c8b15d..891bce85cc 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml
@@ -68,7 +68,6 @@
                 <CollectionView.ItemTemplate>
                     <DataTemplate>
                         <mct:Expander x:DataType="sample:ContentCreator"
-                                      ExpandedChanging="Expander_ExpandedChanging"
                                       ExpandedChanged="Expander_ExpandedChanged">
                             <mct:Expander.Header>
                                 <Label Text="{Binding Name}"/>
diff --git a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
index 984583d14d..9747bdc246 100644
--- a/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
+++ b/samples/CommunityToolkit.Maui.Sample/Pages/Views/Expander/ExpanderPage.xaml.cs
@@ -1,7 +1,6 @@
 using System.Diagnostics.CodeAnalysis;
 using CommunityToolkit.Maui.Alerts;
 using CommunityToolkit.Maui.Sample.ViewModels.Views;
-using CommunityToolkit.Maui.Views;
 
 namespace CommunityToolkit.Maui.Sample.Pages.Views;
 
@@ -12,31 +11,10 @@ public ExpanderPage(ExpanderViewModel viewModel) : base(viewModel)
 		InitializeComponent();
 	}
 
-	Dictionary<Expander, long> expandTimes = new();
-
-	void Expander_ExpandedChanging(object? sender, Core.ExpandedChangingEventArgs e)
-	{
-		if (sender is Expander expander)
-		{
-			expandTimes[expander] = DateTime.Now.Ticks;
-		}
-	}
-
 	async void Expander_ExpandedChanged(object? sender, Core.ExpandedChangedEventArgs e)
 	{
 		var collapsedText = e.IsExpanded ? "expanded" : "collapsed";
-		if (sender is Expander expander)
-		{
-			if (expandTimes.TryGetValue(expander, out var startTime))
-			{
-				var elapsed = DateTime.Now.Ticks - startTime;
-				await Toast.Make($"Expander is {collapsedText} ({elapsed} ms)").Show(CancellationToken.None);
-			}
-			else
-			{
-				await Toast.Make($"Expander is {collapsedText}").Show(CancellationToken.None);
-			}
-		}
+		await Toast.Make($"Expander is {collapsedText}").Show(CancellationToken.None);
 	}
 
 	async void GoToCSharpSampleClicked(object? sender, EventArgs? e)
diff --git a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
index 4dc5a22b39..32cfff54b5 100644
--- a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
+++ b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
@@ -1,5 +1,4 @@
 using CommunityToolkit.Maui.Core;
-using CommunityToolkit.Maui.Views;
 
 namespace CommunityToolkit.Maui.Behaviors;
 
@@ -32,7 +31,7 @@ public partial class ExpanderAnimationBehavior : BaseBehavior<Views.Expander>, I
 	[BindableProperty]
 	public partial uint ExpandingLength { get; set; } = ExpanderAnimationBehaviorDefaults.ExpandingLength;
 
-	IExpansionController previousController = InstantExpansionController.Instance;
+	IExpansionController? previousController;
 
 	/// <summary>
 	/// Attaches the behavior to the specified expander and assigns it as the controller responsible for handling expansion animations.
@@ -41,7 +40,7 @@ public partial class ExpanderAnimationBehavior : BaseBehavior<Views.Expander>, I
 	protected override void OnAttachedTo(Views.Expander bindable)
 	{
 		base.OnAttachedTo(bindable);
-		previousController = bindable.ExpansionController ?? InstantExpansionController.Instance;
+		previousController = bindable.ExpansionController;
 		bindable.ExpansionController = this;
 	}
 
@@ -66,7 +65,7 @@ public async Task OnExpandingAsync(Views.Expander expander)
 	{
 		if (expander.ContentHost is ContentView host && expander.Content is View view)
 		{
-			var tcs = new TaskCompletionSource();
+			var tcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, 0, size.Height);
 			animation.Commit(expander, "ExpanderAnimation", 16, ExpandingLength, ExpandingEasing,
@@ -83,7 +82,7 @@ public async Task OnCollapsingAsync(Views.Expander expander)
 	{
 		if (expander.ContentHost is ContentView host && expander.Content is View view)
 		{
-			var tcs = new TaskCompletionSource();
+			var tcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, size.Height, 0);
 			animation.Commit(expander, "ExpanderAnimation", 16, CollapsingLength, CollapsingEasing,
diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index 4aa0b88900..f4d1417d17 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -70,7 +70,7 @@ public event EventHandler<ExpandedChangedEventArgs> ExpandedChanged
 	/// <summary>
 	/// Gets or sets a value indicating whether the expander is expanded.
 	/// </summary>
-	[BindableProperty(PropertyChangedMethodName = nameof(OnIsExpandedPropertyChanged))]
+	[BindableProperty(PropertyChangingMethodName = nameof(OnIsExpandedPropertyChanging), PropertyChangedMethodName = nameof(OnIsExpandedPropertyChanged))]
 	public partial bool IsExpanded { get; set; }
 
 	/// <summary>
@@ -90,7 +90,7 @@ public event EventHandler<ExpandedChangedEventArgs> ExpandedChanged
 	/// logic for this expander, including any optional animations.
 	/// </summary>
 	[BindableProperty]
-	public partial IExpansionController ExpansionController { get; set; } = InstantExpansionController.Instance;
+	public partial IExpansionController? ExpansionController { get; set; }
 
 	/// <summary>
 	/// The Action that fires when <see cref="Header"/> is tapped.
@@ -170,6 +170,12 @@ static void OnHeaderPropertyChanged(BindableObject bindable, object oldValue, ob
 		}
 	}
 
+	static void OnIsExpandedPropertyChanging(BindableObject bindable, object oldValue, object newValue)
+	{
+		Expander expander = (Expander)bindable;
+		expander.expandedChangingEventManager.HandleEvent(expander, new ExpandedChangingEventArgs((bool)oldValue, (bool)newValue), nameof(ExpandedChanging));
+	}
+
 	static void OnIsExpandedPropertyChanged(BindableObject bindable, object oldValue, object newValue)
 	{
 		((IExpander)bindable).ExpandedChanged(((IExpander)bindable).IsExpanded);
@@ -277,21 +283,20 @@ void IExpander.ExpandedChanged(bool isExpanded)
 
 	async Task ExpandedChangedAsync(bool wasExpanded, bool isExpanded)
 	{
-		expandedChangingEventManager.HandleEvent(this, new ExpandedChangingEventArgs(wasExpanded, isExpanded), nameof(ExpandedChanging));
-
 		try
 		{
 			if (ContentHost is ContentView host && Content is View view)
 			{
+				IExpansionController controller = ExpansionController ?? InstantExpansionController.Instance;
 				if (!wasExpanded && isExpanded)
 				{
 					view.IsVisible = true;
-					await ExpansionController.OnExpandingAsync(this);
+					await controller.OnExpandingAsync(this);
 					host.HeightRequest = -1;
 				}
 				else
 				{
-					await ExpansionController.OnCollapsingAsync(this);
+					await controller.OnCollapsingAsync(this);
 					host.HeightRequest = 0;
 					view.IsVisible = false;
 				}

From c38ce1c83112e7cc4d6f3a927abc7b4fb9342d12 Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 20:15:04 +1100
Subject: [PATCH 07/10] Create expansionGate early

---
 .../Views/Expander/Expander.shared.cs              | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index f4d1417d17..5a7e1996b3 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -173,6 +173,7 @@ static void OnHeaderPropertyChanged(BindableObject bindable, object oldValue, ob
 	static void OnIsExpandedPropertyChanging(BindableObject bindable, object oldValue, object newValue)
 	{
 		Expander expander = (Expander)bindable;
+		expander.expansionGate = new();
 		expander.expandedChangingEventManager.HandleEvent(expander, new ExpandedChangingEventArgs((bool)oldValue, (bool)newValue), nameof(ExpandedChanging));
 	}
 
@@ -223,22 +224,11 @@ void OnHeaderTapGestureRecognizerTapped(object? sender, TappedEventArgs tappedEv
 
 	TaskCompletionSource expansionGate = new();
 
-	Task WaitForExpandedChangedAsync()
-	{
-		if (!expansionGate.Task.IsCompleted)
-		{
-			return expansionGate.Task;
-		}
-
-		expansionGate = new(TaskCreationOptions.RunContinuationsAsynchronously);
-		return expansionGate.Task;
-	}
-
 	void ResizeExpanderInItemsView(TappedEventArgs tappedEventArgs)
 	{
 		_ = Dispatcher.Dispatch(async () =>
 		{
-			await WaitForExpandedChangedAsync();
+			await expansionGate.Task;
 			ResizeExpanderInItemsView2(tappedEventArgs);
 		});
 	}

From b8e57855de8a8e2b1eb7f686efb3fc31ef673856 Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 20:38:14 +1100
Subject: [PATCH 08/10] Reset Expander.ContentHost when Expander.Content is
 cleared

---
 .../Views/Expander/ExpanderTests.cs                | 10 ++++++++++
 .../Views/Expander/Expander.shared.cs              | 14 ++++++++------
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
index 196aafea80..571b932ed3 100644
--- a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
+++ b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
@@ -240,6 +240,16 @@ public async Task OnExpandingAsyncAnimatesHeightCorrectly()
 		Assert.True(element.IsVisible);
 	}
 
+	[Fact]
+	public async Task ExpanderContentHostIsUnsetWhenContentIsRemoved()
+	{
+		var expander = new Expander();
+		expander.Content = new Label { Text = "Hello" };
+		Assert.NotNull(expander.ContentHost);
+		expander.Content = (IView)null!;
+		Assert.Null(expander.ContentHost);
+	}
+
 	class MockExpansionController : IExpansionController
 	{
 		public event EventHandler? Expanding;
diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index 5a7e1996b3..2412cae1fa 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -125,13 +125,15 @@ static void OnExpandDirectionChanging(BindableObject bindable, object oldValue,
 	static void OnContentPropertyChanged(BindableObject bindable, object oldValue, object newValue)
 	{
 		var expander = (Expander)bindable;
-		if (newValue is View view)
+
+		if (expander.ContentHost is not null)
 		{
-			if (expander.ContentHost is not null)
-			{
-				expander.ContentGrid.Remove(expander.ContentHost);
-			}
+			expander.ContentGrid.Remove(expander.ContentHost);
+			expander.ContentHost = null;
+		}
 
+		if (newValue is View view)
+		{
 			// Initialize content visibility and height based on the current expansion state
 			view.IsVisible = expander.IsExpanded;
 			expander.ContentHost = new ContentView
@@ -173,7 +175,7 @@ static void OnHeaderPropertyChanged(BindableObject bindable, object oldValue, ob
 	static void OnIsExpandedPropertyChanging(BindableObject bindable, object oldValue, object newValue)
 	{
 		Expander expander = (Expander)bindable;
-		expander.expansionGate = new();
+		expander.expansionGate = new(TaskCreationOptions.RunContinuationsAsynchronously);
 		expander.expandedChangingEventManager.HandleEvent(expander, new ExpandedChangingEventArgs((bool)oldValue, (bool)newValue), nameof(ExpandedChanging));
 	}
 

From 8036ab482d00b39d6645bc926282c615d2882b5f Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 20:41:47 +1100
Subject: [PATCH 09/10] Windows workaround no longer needed?

---
 src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
index 2412cae1fa..d18c444ae7 100644
--- a/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
+++ b/src/CommunityToolkit.Maui/Views/Expander/Expander.shared.cs
@@ -243,11 +243,6 @@ void ResizeExpanderInItemsView2(TappedEventArgs tappedEventArgs)
 		}
 
 		Element element = this;
-#if WINDOWS
-		var size = IsExpanded
-					? Measure(double.PositiveInfinity, double.PositiveInfinity)
-					: Header.Measure(double.PositiveInfinity, double.PositiveInfinity);
-#endif
 		while (element is not null)
 		{
 #if IOS || MACCATALYST

From 42899471cfd18b7f6b3da72aff36d160df27392a Mon Sep 17 00:00:00 2001
From: Stephen Quan <squan@esri.com>
Date: Mon, 2 Mar 2026 22:19:19 +1100
Subject: [PATCH 10/10] Updated unit test. Refactored ExpanderAnimationBehavior
 animations.

---
 .../Views/Expander/ExpanderTests.cs                       | 4 ++--
 .../Behaviors/ExpanderAnimationBehavior.shared.cs         | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
index 571b932ed3..30b490c317 100644
--- a/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
+++ b/src/CommunityToolkit.Maui.UnitTests/Views/Expander/ExpanderTests.cs
@@ -241,12 +241,12 @@ public async Task OnExpandingAsyncAnimatesHeightCorrectly()
 	}
 
 	[Fact]
-	public async Task ExpanderContentHostIsUnsetWhenContentIsRemoved()
+	public void ExpanderContentHostIsUnsetWhenContentIsRemoved()
 	{
 		var expander = new Expander();
 		expander.Content = new Label { Text = "Hello" };
 		Assert.NotNull(expander.ContentHost);
-		expander.Content = (IView)null!;
+		expander.SetValue(Expander.ContentProperty, null);
 		Assert.Null(expander.ContentHost);
 	}
 
diff --git a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
index 32cfff54b5..86d826b36e 100644
--- a/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
+++ b/src/CommunityToolkit.Maui/Behaviors/ExpanderAnimationBehavior.shared.cs
@@ -68,9 +68,9 @@ public async Task OnExpandingAsync(Views.Expander expander)
 			var tcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, 0, size.Height);
-			animation.Commit(expander, "ExpanderAnimation", 16, ExpandingLength, ExpandingEasing,
-				(v, c) => { tcs.TrySetResult(); host.HeightRequest = -1; });
+			animation.Commit(expander, "ExpanderAnimation", 16, ExpandingLength, ExpandingEasing, (v, c) => tcs.TrySetResult());
 			await tcs.Task;
+			host.HeightRequest = -1;
 		}
 	}
 
@@ -85,9 +85,9 @@ public async Task OnCollapsingAsync(Views.Expander expander)
 			var tcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 			var size = view.Measure(host.Width, double.PositiveInfinity);
 			var animation = new Animation(v => host.HeightRequest = v, size.Height, 0);
-			animation.Commit(expander, "ExpanderAnimation", 16, CollapsingLength, CollapsingEasing,
-				(v, c) => { tcs.TrySetResult(); host.HeightRequest = 0; });
+			animation.Commit(expander, "ExpanderAnimation", 16, CollapsingLength, CollapsingEasing, (v, c) => tcs.TrySetResult());
 			await tcs.Task;
+			host.HeightRequest = 0;
 		}
 	}
 }