Ensure an exact measure for the nested horizontal scrollview

src/Core/src/Platform/Android/MauiScrollView.cs

@@ -2,6 +2,7 @@
 using Android.Animation;
 using Android.Content;
 using Android.Graphics;
+using Android.Hardware.Lights;
 using Android.Runtime;
 using Android.Util;
 using Android.Views;
@@ -189,12 +190,20 @@ protected override void OnLayout(bool changed, int left, int top, int right, int
 
 			if (_hScrollView?.Parent == this && _content is not null)
 			{
-				double scrollViewContentHeight = _content.Height;
+				var scrollViewContentHeight = _content.Height;
 				var hScrollViewHeight = bottom - top;
+				var hScrollViewWidth = right - left;
+
 				//if we are scrolling both ways we need to lay out our MauiHorizontalScrollView with more than the available height
 				//so its parent the NestedScrollView can scroll vertically
-				var newBottom = _isBidirectional ? Math.Max(hScrollViewHeight, scrollViewContentHeight) : hScrollViewHeight;
-				_hScrollView.Layout(0, 0, right - left, (int)newBottom);
+				hScrollViewHeight = _isBidirectional ? Math.Max(hScrollViewHeight, scrollViewContentHeight) : hScrollViewHeight;
+
+				// Ensure that the horizontal scrollview has been measured at the actual target size
+				// so that it updates its internal bookkeeping to use the full size
+				_hScrollView.Measure(MeasureSpec.MakeMeasureSpec(right - left, MeasureSpecMode.Exactly),
+					MeasureSpec.MakeMeasureSpec(hScrollViewHeight, MeasureSpecMode.Exactly));
+
+				_hScrollView.Layout(0, 0, hScrollViewWidth, hScrollViewHeight);
 			}
 
 			if (CrossPlatformArrange == null)
@@ -301,6 +310,7 @@ protected MauiHorizontalScrollView(IntPtr javaReference, JniHandleOwnership tran
 		public MauiHorizontalScrollView(Context? context, MauiScrollView parentScrollView) : base(context)
 		{
 			_parentScrollView = parentScrollView;
+			Tag = "Microsoft.Maui.Android.HorizontalScrollView";
 		}
 
 		public MauiHorizontalScrollView(Context? context, IAttributeSet? attrs) : base(context, attrs)

src/Core/tests/DeviceTests/Handlers/ScrollView/ScrollViewHandlerTests.Android.cs

@@ -1,12 +1,14 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
+using Android.Widget;
 using AndroidX.AppCompat.Widget;
 using AndroidX.Core.Widget;
 using Microsoft.Maui.DeviceTests.Stubs;
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Handlers;
 using Xunit;
+using static Android.Views.View;
 
 namespace Microsoft.Maui.DeviceTests
 {
@@ -99,5 +101,33 @@ public async Task VerticalVisibilityInitializesCorrectly(ScrollBarVisibility vis
 
 			Assert.Equal(expected, result);
 		}
+
+		[Fact]
+		public async Task MauiScrollViewGetsFullHeightInHorizontalOrientation()
+		{
+			await InvokeOnMainThreadAsync(() =>
+			{
+				var sv = new MauiScrollView(MauiContext.Context);
+				sv.SetOrientation(ScrollOrientation.Horizontal);
+				var content = new Button(MauiContext.Context);
+				sv.SetContent(content);
+
+				var hsv = sv.FindViewWithTag("Microsoft.Maui.Android.HorizontalScrollView") as MauiHorizontalScrollView;
+
+				Assert.NotNull(hsv);
+
+				sv.Measure(
+					MeasureSpec.MakeMeasureSpec(1000, Android.Views.MeasureSpecMode.Exactly),
+					MeasureSpec.MakeMeasureSpec(1000, Android.Views.MeasureSpecMode.Exactly));
+
+				sv.Layout(0, 0, 1000, 1000);
+
+				var measuredWidth = hsv.MeasuredWidth;
+				var measuredHeight = hsv.MeasuredHeight;
+
+				Assert.Equal(1000, measuredWidth);
+				Assert.Equal(1000, measuredHeight);
+			});
+		}
 	}
 }