[iOS] Flyout Menu CollectionView First Item Misaligned - fix (#30501)

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### Description of Change

The regression is caused by this PR:
#28670, but I think that the changes
introduced by @albyrock87 let us simplify the code and easily fix the
regression

### Issues Fixed

Fixes #30483

|Before|After|
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src="https://github.com/user-attachments/assets/fdc507b6-a156-4175-944d-efdf8d22340e"
width="300px"></video>|<video
src="https://github.com/user-attachments/assets/a8dcddae-65b7-4047-82f7-c876907720e4"
width="300px"></video>|

Author: jfversluis

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellFlyoutLayoutManager.cs

@@ -199,43 +199,10 @@ internal void UpdateHeaderSize()
 				HeaderView.SizeThatFits(new CGSize(ContentView.Superview.Frame.Width, double.PositiveInfinity));
 			}
 
-			SetHeaderContentInset();
 			UpdateHeaderMaximumSize(ScrollView?.ContentOffset.Y);
 			LayoutParallax();
 		}
 
-
-		internal void SetHeaderContentInset()
-		{
-			if (ScrollView is null)
-				return;
-
-			var offset = ScrollView.ContentInset.Top;
-
-			if (HeaderView is not null)
-			{
-				if (double.IsNaN(MeasuredHeaderViewHeightWithNoMargin))
-				{
-					return;
-				}
-
-				// We take the measured header height without margin, since the margin is already accounted for in the positioning of the scroll view itself.
-				ScrollView.ContentInset = new UIEdgeInsets((nfloat)Math.Max(HeaderMinimumHeight, MeasuredHeaderViewHeightWithNoMargin), 0, 0, 0);
-			}
-			else
-			{
-				ScrollView.ContentInset = new UIEdgeInsets(UIApplication.SharedApplication.GetSafeAreaInsetsForWindow().Top, 0, 0, 0);
-			}
-
-			offset -= ScrollView.ContentInset.Top;
-
-			var yContentOffset = ScrollView.ContentOffset.Y;
-			ScrollView.ContentOffset =
-				new CGPoint(ScrollView.ContentOffset.X, yContentOffset + offset);
-
-			UpdateVerticalScrollMode();
-		}
-
 		public void UpdateVerticalScrollMode()
 		{
 			if (ScrollView is null)
@@ -319,17 +286,7 @@ void LayoutContent(CGRect parentBounds, nfloat footerHeight)
 
 			if (HeaderView is not null)
 			{
-				if (ScrollView is null)
-				{
-					// The margin is already managed by MAUI's layout system, so we don't need to add it here and we just offset the content by the header's height.				
-					contentYOffset += HeaderView.Frame.Height;
-				}
-				else
-				{
-					// For ScrollView, we need to consider the margin, but we should not consider the header height, since it should overlap with the scroll view. 
-					// The content inset is already managed by SetHeaderContentInset.
-					contentYOffset += HeaderView.View.Margin.VerticalThickness;
-				}
+				contentYOffset += HeaderView.Frame.Height;
 			}
 
 			var contentFrame = new Rect(parentBounds.X, contentYOffset, parentBounds.Width, parentBounds.Height - contentYOffset - footerHeight);
@@ -356,7 +313,6 @@ void OnShellPropertyChanged(object sender, PropertyChangedEventArgs e)
 		{
 			if (e.Is(Shell.FlyoutHeaderBehaviorProperty))
 			{
-				SetHeaderContentInset();
 				LayoutParallax();
 			}
 			else if (e.Is(Shell.FlyoutVerticalScrollModeProperty))

src/Controls/src/Core/Compatibility/Handlers/Shell/iOS/ShellTableViewController.cs

@@ -94,7 +94,6 @@ public override void ViewDidLoad()
 		[System.Runtime.Versioning.SupportedOSPlatform("tvos11.0")]
 		public override void ViewSafeAreaInsetsDidChange()
 		{
-			ShellFlyoutContentManager.SetHeaderContentInset();
 			base.ViewSafeAreaInsetsDidChange();
 		}
 

src/Controls/tests/TestCases.Android.Tests/snapshots/android/FlyoutMenuCollectionViewFirstItemMisaligned.png

@@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Shell xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+       xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+       x:Class="Maui.Controls.Sample.Issues.Issue30483">
+    <Shell.FlyoutHeader>
+        <Grid Padding="10">
+            <Image Background="Red"
+                   Aspect="AspectFit"
+                   Source="dotnet_bot.png">
+            </Image>
+        </Grid>
+    </Shell.FlyoutHeader>
+
+    <Shell.FlyoutContent>
+        <CollectionView x:Name="CollectionView"
+            AutomationId="CollectionView"
+                        Margin="10"
+                        BackgroundColor="Green">
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <HorizontalStackLayout Padding="10">
+                        <Label Text="{Binding .}"
+                               FontSize="20"
+                               HorizontalOptions="Center"/>
+                        <Image Source="dotnet_bot.png"
+                               Aspect="AspectFit"
+                               HorizontalOptions="Center"
+                               VerticalOptions="CenterAndExpand"/>
+                    </HorizontalStackLayout>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+            <CollectionView.ItemsSource>
+                <x:Array Type="{x:Type x:String}">
+                    <x:String>Item 1</x:String>
+                    <x:String>Item 2</x:String>
+                    <x:String>Item 3</x:String>
+                    <x:String>Item 4</x:String>
+                    <x:String>Item 5</x:String>
+                    <x:String>Item 6</x:String>
+                    <x:String>Item 7</x:String>
+                </x:Array>
+            </CollectionView.ItemsSource>
+        </CollectionView>
+    </Shell.FlyoutContent>
+
+    <Shell.FlyoutFooter>
+        <Button Margin="10"
+                Text="User Settings"
+                Background="CornflowerBlue"
+                HorizontalOptions="Fill"
+                VerticalOptions="Fill"/>
+    </Shell.FlyoutFooter>
+
+    <FlyoutItem Route="MainPage"
+                Title="Main Page"
+                Icon="dotnet_bot.png">
+        <ShellContent>
+            <ContentPage Title="Main Page">
+                <Label Text="Welcome to the Main Page!"
+                       HorizontalOptions="Center"
+                       VerticalOptions="Center"/>
+            </ContentPage>
+        </ShellContent>
+    </FlyoutItem>
+</Shell>

src/Controls/tests/TestCases.HostApp/Issues/Issue30483.xaml

@@ -0,0 +1,12 @@
+namespace Maui.Controls.Sample.Issues
+{
+	[Issue(IssueTracker.Github, 30483, "Flyout Menu CollectionView First Item Misaligned", PlatformAffected.iOS)]
+	public partial class Issue30483 : Shell
+	{
+		public Issue30483()
+		{
+			InitializeComponent();
+			FlyoutIsPresented = true;
+		}
+	}
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue30483.xaml.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue30483 : _IssuesUITest
+{
+	public Issue30483(TestDevice device) : base(device) { }
+
+	public override string Issue => "Flyout Menu CollectionView First Item Misaligned";
+
+	[Test]
+	[Category(UITestCategories.CollectionView)]
+	public void FlyoutMenuCollectionViewFirstItemMisaligned()
+	{
+		App.WaitForElement("CollectionView");
+		App.ScrollDown("CollectionView");
+		VerifyScreenshot();
+	}
+}