Fixes footer position not updated on CV1 when clearing all items (#29173)

* Fixes footer position not updated on CV1 when clearing all items

* Fix UITest

Author: albyrock87

src/Controls/src/Core/Handlers/Items/iOS/ItemsViewController.cs

@@ -924,6 +924,12 @@ internal virtual void CellDisplayingEndedFromDelegate(UICollectionViewCell cell,
 					!Equals(itemsSource[indexPath], bindingContext))
 				{
 					templatedCell.Unbind();
+
+					if (CollectionView is MauiCollectionView collectionView)
+					{
+						// When removing a cell, we need to trigger a layout update in order to sync the footer position
+						collectionView.NeedsCellLayout = true;
+					}
 				}
 			}
 		}

src/Controls/tests/TestCases.HostApp/Elements/CollectionView/HeaderFooterGalleries/HeaderFooterView.xaml

@@ -7,7 +7,7 @@
              x:Class=" Maui.Controls.Sample.CollectionViewGalleries.HeaderFooterGalleries.HeaderFooterView">
     <ContentPage.Content>
 
-        <CollectionView x:Name="CollectionView" ItemsSource="{Binding Items}">
+        <CollectionView x:Name="CollectionView" AutomationId="CV" ItemsSource="{Binding Items}">
 
             <CollectionView.Header>
 

src/Controls/tests/TestCases.HostApp/Elements/CollectionView/HeaderFooterGalleries/HeaderFooterView.xaml.cs

@@ -21,17 +21,16 @@ public HeaderFooterViewModel(int count = 50, Func<string, CollectionViewGalleryT
 		{
 		}
 
-		public ICommand AddCommand => new Command(async () => await AddItemsAsync());
+		public ICommand AddCommand => new Command(AddItemsAsync);
 
 		public ICommand ClearCommand => new Command(() => Items.Clear());
 
 		public string HeaderText => "This Is A Header";
 
 		public string FooterText => "This Is A Footer";
 
-		async Task AddItemsAsync()
+		void AddItemsAsync()
 		{
-			await Task.Delay(TimeSpan.FromSeconds(1));
 			AddItems(Items, 2);
 		}
 	}

src/Controls/tests/TestCases.Shared.Tests/Tests/CollectionView/CollectionViewUITests.HeaderAndFooter.cs

@@ -1,4 +1,5 @@
 using NUnit.Framework;
+using NUnit.Framework.Legacy;
 using UITest.Appium;
 using UITest.Core;
 
@@ -31,7 +32,7 @@ public void HeaderFooterStringWorks()
 #if IOS || ANDROID
 		[Test]
         [Category(UITestCategories.CollectionView)]
-        public void HeaderFooterViewWorks()
+        public async Task HeaderFooterViewWorks()
         {
             // Navigate to the selection galleries
             VisitInitialGallery("Header Footer");
@@ -41,6 +42,20 @@ public void HeaderFooterViewWorks()
 
             App.WaitForElement("This Is A Header");
             App.WaitForElement("This Is A Footer");
+
+			// Now let's add items until the footer goes out of the screen
+			// and then remove them all and verify the footer is visible again (#29137)
+			var i = 5;
+			while (--i > 0)
+			{
+				App.WaitForElement("Add 2 Items").Tap();
+				App.ScrollDownTo("Add 2 Items", "CV");				
+			}
+
+            App.WaitForElement("Clear All Items").Tap();
+            await Task.Delay(300);
+
+            ClassicAssert.IsTrue(App.WaitForElement("This Is A Footer").IsDisplayed());
         }
 
 		[Test]