Ensure that viewport calculations for iOS ScrollView account for content insets (#18277)

* Ensure that viewport calculations for iOS ScrollView account for content insets
Fixes #17224

* Update baseline image

Author: hartez

src/Controls/tests/DeviceTests/Elements/ScrollView/ScrollViewTests.iOS.cs

@@ -7,6 +7,7 @@
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Hosting;
+using UIKit;
 using Xunit;
 
 namespace Microsoft.Maui.DeviceTests
@@ -35,5 +36,52 @@ await scrollViewHandler.PlatformView.AttachAndRun(() =>
 				});
 			});
 		}
+
+		[Fact]
+		public async Task ContentSizeExpandsToViewport()
+		{
+			EnsureHandlerCreated(builder => { builder.ConfigureMauiHandlers(handlers => { handlers.AddHandler<Entry, EntryHandler>(); }); });
+
+			var scrollView = new ScrollView();
+	
+			var entry = new Entry() { Text = "In a ScrollView", HeightRequest = 10 };
+			
+
+			static CoreGraphics.CGSize getViewportSize(UIScrollView scrollView)
+			{
+				return scrollView.AdjustedContentInset.InsetRect(scrollView.Bounds).Size;
+			};
+
+			var scrollViewHandler = await InvokeOnMainThreadAsync(() =>
+			{
+				return CreateHandlerAsync<ScrollViewHandler>(scrollView);
+			});
+
+			await InvokeOnMainThreadAsync(async () =>
+			{
+				await scrollViewHandler.PlatformView.AttachAndRun(async () =>
+				{
+					var uiScrollView = scrollViewHandler.PlatformView;
+
+					uiScrollView.ContentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentBehavior.Always;
+					var parent = uiScrollView.Superview;
+					uiScrollView.Bounds = parent.Bounds;
+					uiScrollView.Center = parent.Center;
+
+					scrollView.Content = entry;
+
+					parent.SetNeedsLayout();
+					parent.LayoutIfNeeded();
+
+					await Task.Yield();
+
+					var contentSize = uiScrollView.ContentSize;
+					var viewportSize = getViewportSize(uiScrollView);
+
+					Assert.Equal(viewportSize.Height, contentSize.Height);
+					Assert.Equal(viewportSize.Width, contentSize.Width);
+				});
+			});
+		}
 	}
 }

src/Controls/tests/UITests/snapshots/ios/Issue16094Test.png

@@ -1,13 +1,7 @@
 using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Drawing;
-using System.Text;
 using CoreGraphics;
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Layouts;
-using Microsoft.Maui.Platform;
-using ObjCRuntime;
 using UIKit;
 using Size = Microsoft.Maui.Graphics.Size;
 
@@ -103,9 +97,11 @@ public static void MapOrientation(IScrollViewHandler handler, IScrollView scroll
 			// without having to re-layout the ScrollView
 
 			var fullContentSize = scrollView.PresentedContent?.DesiredSize ?? Size.Zero;
-			var viewportBounds = uiScrollView.Bounds;
+
+			var viewportBounds = GetViewportBounds(uiScrollView);
 			var viewportWidth = viewportBounds.Width;
 			var viewportHeight = viewportBounds.Height;
+
 			SetContentSizeForOrientation(uiScrollView, viewportWidth, viewportHeight, scrollView.Orientation, fullContentSize);
 		}
 
@@ -127,7 +123,7 @@ public static void MapRequestScrollTo(IScrollViewHandler handler, IScrollView sc
 				var availableScrollWidth = uiScrollView.ContentSize.Width - uiScrollView.Frame.Width;
 				var minScrollHorizontal = Math.Min(request.HorizontalOffset, availableScrollWidth);
 				var minScrollVertical = Math.Min(request.VerticalOffset, availableScrollHeight);
-				uiScrollView.SetContentOffset(new CoreGraphics.CGPoint(minScrollHorizontal, minScrollVertical), !request.Instant);
+				uiScrollView.SetContentOffset(new CGPoint(minScrollHorizontal, minScrollVertical), !request.Instant);
 
 				if (request.Instant)
 				{
@@ -185,16 +181,15 @@ static void InsertContentView(UIScrollView platformScrollView, IScrollView scrol
 				return;
 			}
 
-			var contentContainer = new ContentView()
+			var contentContainer = new ContentView
 			{
 				View = scrollView.PresentedContent,
-				Tag = ContentPanelTag
+				Tag = ContentPanelTag,
+				// This is where we normally would inject the cross-platform ScrollView's layout logic; instead, we're injecting the
+				// methods from this handler so it can make some adjustments for things like Padding before the default logic is invoked
+				CrossPlatformLayout = crossPlatformLayout
 			};
 
-			// This is where we normally would inject the cross-platform ScrollView's layout logic; instead, we're injecting the
-			// methods from this handler so it can make some adjustments for things like Padding before the default logic is invoked
-			contentContainer.CrossPlatformLayout = crossPlatformLayout;
-
 			platformScrollView.ClearSubviews();
 			contentContainer.AddSubview(platformContent);
 			platformScrollView.AddSubview(contentContainer);
@@ -289,6 +284,11 @@ static void SetContentSizeForOrientation(UIScrollView uiScrollView, double viewp
 			uiScrollView.ContentSize = contentSize;
 		}
 
+		static CGRect GetViewportBounds(UIScrollView platformScrollView)
+		{
+			return platformScrollView.AdjustedContentInset.InsetRect(platformScrollView.Bounds);
+		}
+
 		Size ICrossPlatformLayout.CrossPlatformMeasure(double widthConstraint, double heightConstraint)
 		{
 			var scrollView = VirtualView;
@@ -301,17 +301,18 @@ Size ICrossPlatformLayout.CrossPlatformMeasure(double widthConstraint, double he
 				return Size.Zero;
 			}
 
-			var scrollViewBounds = platformScrollView.Bounds;
+			var viewPortBounds = GetViewportBounds(platformScrollView);
+
 			var padding = scrollView.Padding;
 
 			if (widthConstraint == 0)
 			{
-				widthConstraint = scrollViewBounds.Width;
+				widthConstraint = viewPortBounds.Width;
 			}
 
 			if (heightConstraint == 0)
 			{
-				heightConstraint = scrollViewBounds.Height;
+				heightConstraint = viewPortBounds.Height;
 			}
 
 			// Account for the ScrollView Padding before measuring the content
@@ -330,29 +331,28 @@ Size ICrossPlatformLayout.CrossPlatformArrange(Rect bounds)
 			var crossPlatformLayout = scrollView as ICrossPlatformLayout;
 			var platformScrollView = PlatformView;
 
-			var contentSize = crossPlatformLayout.CrossPlatformArrange(bounds);
-
 			// The UIScrollView's bounds are available, so we can use them to make sure the ContentSize makes sense
 			// for the ScrollView orientation
-			var viewportBounds = platformScrollView.Bounds;
+			var viewportBounds = GetViewportBounds(platformScrollView);
+
+			var contentSize = crossPlatformLayout.CrossPlatformArrange(viewportBounds.ToRectangle());
+
 			var viewportHeight = viewportBounds.Height;
 			var viewportWidth = viewportBounds.Width;
 			SetContentSizeForOrientation(platformScrollView, viewportWidth, viewportHeight, scrollView.Orientation, contentSize);
 
 			var container = GetContentView(platformScrollView);
 
-			if (container?.Superview is UIScrollView uiScrollView)
+			if (container != null)
 			{
 				// Ensure the container is at least the size of the UIScrollView itself, so that the 
 				// cross-platform layout logic makes sense and the contents don't arrange outside the 
 				// container. (Everything will look correct if they do, but hit testing won't work properly.)
-
-				var scrollViewBounds = uiScrollView.Bounds;
 				var containerBounds = contentSize;
 
 				container.Bounds = new CGRect(0, 0,
-					Math.Max(containerBounds.Width, scrollViewBounds.Width),
-					Math.Max(containerBounds.Height, scrollViewBounds.Height));
+					Math.Max(containerBounds.Width, viewportBounds.Width),
+					Math.Max(containerBounds.Height, viewportBounds.Height));
 
 				container.Center = new CGPoint(container.Bounds.GetMidX(), container.Bounds.GetMidY());
 			}