[Windows] Fix wrong Layout from hidden CollectionView

src/Controls/samples/Controls.Sample.UITests/Issues/Issue17400.xaml

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue17400"
+             xmlns:ns="clr-namespace:Maui.Controls.Sample.Issues"
+             Title="Issue 17400">
+    <Grid
+        Padding="30,0"
+        VerticalOptions="Center"
+        RowDefinitions="*, Auto">
+        <CollectionView 
+            x:Name="ItemsView"
+            ItemsSource="{Binding Items}"
+            IsVisible="{Binding AreItemsVisible}">
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <Grid
+                        HeightRequest="60" 
+                        RowDefinitions=" 30,29,1">
+                        <Label 
+                            AutomationId="WaitForStubControl"
+                            Grid.Row="0" 
+                            Text="{Binding Label}" 
+                            FontSize="20" 
+                            FontAttributes="Bold"/>
+                        <Label 
+                            Grid.Row="1" 
+                            Text="{Binding Description}" 
+                            FontSize="16"/>
+                        <BoxView 
+                            Grid.Row="2" 
+                            HeightRequest="1" 
+                            Color="Red" />
+                    </Grid>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+        </CollectionView>
+        <Button
+            Grid.Row="1"
+            AutomationId="UpdateBtn"
+            Text="Change Visibility"
+            Command="{Binding UpdateCommand}"
+            HorizontalOptions="Center" />
+    </Grid>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue17400.xaml.cs

@@ -0,0 +1,78 @@
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Windows.Input;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	internal class Issue17400Item : BindableObject
+	{
+		public string Label { get; set; }
+
+		public string Description { get; set; }
+	}
+
+	internal class Issue17400ViewModel : BindableObject
+	{
+		ObservableCollection<Issue17400Item> _items;
+		bool _areItemsVisible;
+
+		public Issue17400ViewModel()
+		{
+			List<Issue17400Item> items = new List<Issue17400Item>();
+
+			foreach (var item in Enumerable.Range(0, 20))
+			{
+				items.Add(new Issue17400Item
+				{
+					Label = "Label " + item,
+					Description = "Description " + item,
+				});
+			}
+
+			Items = new ObservableCollection<Issue17400Item>(items);
+			AreItemsVisible = false;
+		}
+
+		public ObservableCollection<Issue17400Item> Items
+		{
+			get { return _items; }
+			set
+			{
+				_items = value;
+				OnPropertyChanged();
+			}
+		}
+
+		public bool AreItemsVisible
+		{
+			get { return _areItemsVisible; }
+			set
+			{
+				_areItemsVisible = value;
+				OnPropertyChanged();
+			}
+		}
+
+		public ICommand UpdateCommand => new Command(Update);
+
+		void Update()
+		{
+			AreItemsVisible = !AreItemsVisible;
+		}
+	}
+
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.Github, 17400, "CollectionView wrong Layout", PlatformAffected.UWP)]
+	public partial class Issue17400 : ContentPage
+	{
+		public Issue17400()
+		{
+			InitializeComponent();
+
+			BindingContext = new Issue17400ViewModel();
+		}
+	}
+}

src/Controls/src/Core/Platform/Windows/CollectionView/FormsGridView.cs

@@ -25,7 +25,6 @@ public FormsGridView()
 			DefaultStyleKey = typeof(FormsGridView);
 
 			RegisterPropertyChangedCallback(ItemsPanelProperty, ItemsPanelChanged);
-			Loaded += OnLoaded;
 		}
 
 		public int Span
@@ -120,11 +119,6 @@ void ItemsPanelChanged(DependencyObject sender, DependencyProperty dp)
 			FindItemsWrapGrid();
 		}
 
-		void OnLoaded(object sender, RoutedEventArgs e)
-		{
-			FindItemsWrapGrid();
-		}
-
 		public void SetEmptyView(FrameworkElement emptyView, View formsEmptyView)
 		{
 			_emptyView = emptyView;
@@ -152,10 +146,10 @@ protected override void OnApplyTemplate()
 
 		protected override global::Windows.Foundation.Size ArrangeOverride(global::Windows.Foundation.Size finalSize)
 		{
-			if (_formsEmptyView != null)
-			{
-				_formsEmptyView.Layout(new Rect(0, 0, finalSize.Width, finalSize.Height));
-			}
+			_formsEmptyView?.Layout(new Rect(0, 0, finalSize.Width, finalSize.Height));
+
+			if (_wrapGrid is null)
+				FindItemsWrapGrid();
 
 			return base.ArrangeOverride(finalSize);
 		}

src/Controls/tests/UITests/Tests/Issues/Issue17400.cs

@@ -0,0 +1,27 @@
+using Microsoft.Maui.Appium;
+using NUnit.Framework;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+	public class Issue17400 : _IssuesUITest
+	{
+		public Issue17400(TestDevice device)
+			: base(device)
+		{ }
+
+		public override string Issue => "CollectionView wrong Layout";
+
+		[Test]
+		public void Issue17400Test()
+		{
+			UITestContext.IgnoreIfPlatforms(new TestDevice[] { TestDevice.iOS, TestDevice.Android, TestDevice.Mac },
+				"Is a Windows issue; see https://github.com/dotnet/maui/issues/17400");
+
+			App.WaitForElement("UpdateBtn");
+			App.Tap("UpdateBtn");
+
+			App.WaitForElement("WaitForStubControl");
+			VerifyScreenshot();
+		}
+	}
+}