Ensure the iOS ScrollView content container is at least the ScrollVie…

…w size (#8451)

Co-authored-by: Shane Neuville <[email protected]>

src/Controls/src/Core/HandlerImpl/ScrollView/ScrollView.Impl.cs

@@ -94,8 +94,8 @@ Size IContentView.CrossPlatformArrange(Rect bounds)
 				// Normally we'd just want the content to be arranged within the ContentView's Frame,
 				// but ScrollView content might be larger than the ScrollView itself (for obvious reasons)
 				// So in each dimension, we assume the larger of the two values.
-				bounds.Width = Math.Max(Frame.Width, presentedContent.DesiredSize.Width + padding.HorizontalThickness);
-				bounds.Height = Math.Max(Frame.Height, presentedContent.DesiredSize.Height + padding.VerticalThickness);
+				bounds.Width = Math.Max(bounds.Width, presentedContent.DesiredSize.Width + padding.HorizontalThickness);
+				bounds.Height = Math.Max(bounds.Height, presentedContent.DesiredSize.Height + padding.VerticalThickness);
 
 				this.ArrangeContent(bounds);
 			}

src/Core/src/Handlers/ScrollView/ScrollViewHandler.iOS.cs

@@ -1,11 +1,13 @@
 using System;
 using System.Collections.Generic;
+using System.Drawing;
 using System.Text;
 using CoreGraphics;
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Layouts;
 using ObjCRuntime;
 using UIKit;
+using Size = Microsoft.Maui.Graphics.Size;
 
 namespace Microsoft.Maui.Handlers
 {
@@ -56,13 +58,6 @@ public static void MapContent(IScrollViewHandler handler, IScrollView scrollView
 		public static void MapContentSize(IScrollViewHandler handler, IScrollView scrollView)
 		{
 			handler.PlatformView.UpdateContentSize(scrollView.ContentSize);
-
-			if (GetContentView(handler.PlatformView) is ContentView currentContentContainer)
-			{
-				var rect = new Rect(Point.Zero, scrollView.ContentSize);
-				currentContentContainer.Center = new CGPoint(rect.Center.X, rect.Center.Y);
-				currentContentContainer.Bounds = new CGRect(currentContentContainer.Bounds.X, currentContentContainer.Bounds.Y, rect.Width, rect.Height);
-			}
 		}
 
 		public static void MapIsEnabled(IScrollViewHandler handler, IScrollView scrollView)
@@ -131,6 +126,7 @@ static void UpdateContentView(IScrollView scrollView, IScrollViewHandler handler
 				{
 					currentContentContainer.ClearSubviews();
 					currentContentContainer.AddSubview(nativeContent);
+					currentContentContainer.View = scrollView.PresentedContent;
 				}
 			}
 			else
@@ -148,16 +144,41 @@ static void InsertContentView(UIScrollView platformScrollView, IScrollView scrol
 
 			var contentContainer = new ContentView()
 			{
+				View = scrollView.PresentedContent,
 				CrossPlatformMeasure = ConstrainToScrollView(scrollView.CrossPlatformMeasure, platformScrollView, scrollView),
-				CrossPlatformArrange = scrollView.CrossPlatformArrange,
 				Tag = ContentPanelTag
 			};
 
+			contentContainer.CrossPlatformArrange = ArrangeScrollViewContent(scrollView.CrossPlatformArrange, contentContainer);
+
 			platformScrollView.ClearSubviews();
 			contentContainer.AddSubview(platformContent);
 			platformScrollView.AddSubview(contentContainer);
 		}
 
+		static Func<Rect, Size> ArrangeScrollViewContent(Func<Rect, Size> internalArrange, ContentView container)
+		{
+			return (rect) =>
+			{
+				if (container.Superview is UIScrollView scrollView)
+				{
+					// 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 out side the 
+					// container. (Everything will look correct if they do, but hit testing won't work properly.)
+
+					var scrollViewBounds = scrollView.Bounds;
+					var containerBounds = container.Bounds;
+
+					container.Bounds = new CGRect(0, 0, 
+						Math.Max(containerBounds.Width, scrollViewBounds.Width), 
+						Math.Max(containerBounds.Height, scrollViewBounds.Height));
+					container.Center = new CGPoint(container.Bounds.GetMidX(), container.Bounds.GetMidY());
+				}
+
+				return internalArrange(rect);
+			};
+		}
+
 		static Func<double, double, Size> ConstrainToScrollView(Func<double, double, Size> internalMeasure, UIScrollView platformScrollView, IScrollView scrollView)
 		{
 			return (widthConstraint, heightConstraint) =>
@@ -176,20 +197,19 @@ static Size MeasureScrollViewContent(double widthConstraint, double heightConstr
 
 			if (widthConstraint == 0)
 			{
-				widthConstraint = platformScrollView.Frame.Width;
+				widthConstraint = platformScrollView.Bounds.Width;
 			}
 
 			if (heightConstraint == 0)
 			{
-				heightConstraint = platformScrollView.Frame.Height;
+				heightConstraint = platformScrollView.Bounds.Height;
 			}
 
 			widthConstraint -= scrollView.Padding.HorizontalThickness;
 			heightConstraint -= scrollView.Padding.VerticalThickness;
 
 			var result = internalMeasure.Invoke(widthConstraint, heightConstraint);
 
-			// If the presented content has LayoutAlignment Fill, we'll need to adjust the measurement to account for that
 			return result.AdjustForFill(new Rect(0, 0, widthConstraint, heightConstraint), presentedContent);
 		}
 	}