fix: Apply zoom and content offset simultaneously on iOS

Author: MartinZikmund

src/Uno.UI/UI/Xaml/Controls/ListViewBase/ListViewBaseScrollContentPresenter.iOS.cs

@@ -2,11 +2,10 @@
 using System.Collections.Generic;
 using System.Text;
 using CoreGraphics;
+using UIKit;
 using Uno.Extensions;
-
 using Uno.Foundation.Logging;
 using Windows.Foundation;
-using UIKit;
 
 #if NET6_0_OR_GREATER
 using ObjCRuntime;
@@ -26,6 +25,44 @@ public UIEdgeInsets ContentInset
 
 		Size? IScrollContentPresenter.CustomContentExtent => NativePanel?.ContentSize;
 
+		CGPoint IUIScrollView.ContentOffset => NativePanel?.ContentOffset ?? default(CGPoint);
+
+		nfloat IUIScrollView.ZoomScale => NativePanel?.ZoomScale ?? default(nfloat);
+
+		void IUIScrollView.ApplyZoomScale(nfloat scale, bool animated)
+		{
+			if (NativePanel == null)
+			{
+				return;
+			}
+
+			if (animated)
+			{
+				NativePanel.SetZoomScale(scale, animated);
+			}
+			else
+			{
+				NativePanel.ZoomScale = scale;
+			}
+		}
+
+		void IUIScrollView.ApplyContentOffset(CGPoint contentOffset, bool animated)
+		{
+			if (NativePanel == null)
+			{
+				return;
+			}
+
+			if (animated)
+			{
+				NativePanel.SetContentOffset(contentOffset, animated);
+			}
+			else
+			{
+				NativePanel.ContentOffset = contentOffset;
+			}
+		}
+
 		public void SetContentOffset(CGPoint contentOffset, bool animated)
 		{
 			NativePanel?.SetContentOffset(contentOffset, animated);

src/Uno.UI/UI/Xaml/Controls/ScrollContentPresenter/IUIScrollView.iOSmacOS.cs

@@ -13,10 +13,14 @@ internal interface IUIScrollView
 	{
 		CGPoint UpperScrollLimit { get; }
 
-		void SetContentOffset(CGPoint contentOffset, bool animated);
+		CGPoint ContentOffset { get; }
+
+		void ApplyContentOffset(CGPoint contentOffset, bool animated);
 
 #if __IOS__
-		void SetZoomScale(nfloat scale, bool animated);
+		nfloat ZoomScale { get; }
+
+		void ApplyZoomScale(nfloat scale, bool animated);
 #endif
 	}
 }

src/Uno.UI/UI/Xaml/Controls/ScrollContentPresenter/NativeScrollContentPresenter.iOS.cs

@@ -43,6 +43,11 @@ partial class NativeScrollContentPresenter : UIScrollView, DependencyObject, ISe
 		private bool _isInAnimatedScroll;
 
 		CGPoint IUIScrollView.UpperScrollLimit => UpperScrollLimit;
+
+		CGPoint IUIScrollView.ContentOffset => ContentOffset;
+
+		nfloat IUIScrollView.ZoomScale => ZoomScale;
+
 		internal CGPoint UpperScrollLimit
 		{
 			get
@@ -158,6 +163,30 @@ public override void SetContentOffset(CGPoint contentOffset, bool animated)
 			}
 		}
 
+		void IUIScrollView.ApplyZoomScale(nfloat scale, bool animated)
+		{
+			if (!animated)
+			{
+				ZoomScale = scale;
+			}
+			else
+			{
+				base.SetZoomScale(scale, true);
+			}
+		}
+
+		void IUIScrollView.ApplyContentOffset(CGPoint contentOffset, bool animated)
+		{
+			if (!animated)
+			{
+				ContentOffset = contentOffset;
+			}
+			else
+			{
+				base.SetContentOffset(contentOffset, true);
+			}
+		}
+
 		partial void OnContentChanged(UIView previousView, UIView newView)
 		{
 			// If Content is a view it may have already been set as Content somewhere else in certain scenarios
@@ -166,7 +195,7 @@ partial void OnContentChanged(UIView previousView, UIView newView)
 				previousView.RemoveFromSuperview();
 			}
 
-            // Ensure we're working with an empty view, in case previously removed views were missed.
+			// Ensure we're working with an empty view, in case previously removed views were missed.
 			while (Subviews.Length > 0)
 			{
 				Subviews[0].RemoveFromSuperview();
@@ -534,7 +563,7 @@ public override void TouchesBegan(NSSet touches, UIEvent evt)
 				//							  (e.g. it would prevent all sub-sequent events for the given pointer).
 
 				_touchTarget = parent;
-				_touchTarget.TouchesBegan(touches, evt, canBubbleNatively: true); 
+				_touchTarget.TouchesBegan(touches, evt, canBubbleNatively: true);
 			}
 		}
 

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.iOS.cs

@@ -86,24 +86,31 @@ private bool ChangeViewNative(double? horizontalOffset, double? verticalOffset,
 				var desiredOffsets = new Windows.Foundation.Point(horizontalOffset ?? HorizontalOffset, verticalOffset ?? VerticalOffset);
 				var clampedOffsets = new Windows.Foundation.Point(MathEx.Clamp(desiredOffsets.X, 0, limit.X), MathEx.Clamp(desiredOffsets.Y, 0, limit.Y));
 
+				var contentOffsetChange =
+					(horizontalOffset != null && _scrollableContainer.ContentOffset.X != horizontalOffset) ||
+					(verticalOffset != null && _scrollableContainer.ContentOffset.Y != verticalOffset);
+
+				var zoomFactorChange = zoomFactor != null && _scrollableContainer.ZoomScale != zoomFactor;
+
 				var success = desiredOffsets == clampedOffsets;
+
+				if (zoomFactor is { } zoom && zoom != _scrollableContainer.ZoomScale)
+				{
+					_scrollableContainer.ApplyZoomScale(zoom, !disableAnimation);
+				}
+
 				if (!success && IsArrangeDirty)
 				{
 					// If the the requested offsets are out-of - bounds, but we actually does have our final bounds yet,
 					// we allow to set the desired offsets. If needed, they will then be clamped by the OnAfterArrange().
 					// This is needed to allow a ScrollTo before the SV has been layouted.
 
 					_pendingChangeView = (horizontalOffset, verticalOffset, disableAnimation);
-					_scrollableContainer.SetContentOffset(desiredOffsets, !disableAnimation);
+					_scrollableContainer.ApplyContentOffset(desiredOffsets, !disableAnimation);
 				}
 				else
 				{
-					_scrollableContainer.SetContentOffset(clampedOffsets, !disableAnimation);
-				}
-
-				if(zoomFactor is { } zoom)
-				{
-					ChangeViewZoom(zoom, disableAnimation);
+					_scrollableContainer.ApplyContentOffset(clampedOffsets, !disableAnimation);
 				}
 
 				// Return true if successfully scrolled to asked offsets
@@ -130,11 +137,6 @@ partial void OnZoomModeChangedPartial(ZoomMode zoomMode)
 			}
 		}
 
-		private void ChangeViewZoom(float zoomFactor, bool disableAnimation)
-		{
-			_scrollableContainer?.SetZoomScale(zoomFactor, animated: !disableAnimation);
-		}
-
 		private void UpdateZoomedContentAlignment()
 		{
 			if (ZoomFactor != 1 && Content is IFrameworkElement fe)

src/Uno.UI/UI/Xaml/Controls/TextBox/MultilineTextBoxView.iOS.cs

@@ -30,6 +30,30 @@ public partial class MultilineTextBoxView : UITextView, ITextBoxView, Dependency
 
 		CGPoint IUIScrollView.UpperScrollLimit { get { return (CGPoint)(ContentSize - Frame.Size); } }
 
+		void IUIScrollView.ApplyZoomScale(nfloat scale, bool animated)
+		{
+			if (animated)
+			{
+				SetZoomScale(scale, animated);
+			}
+			else
+			{
+				ZoomScale = scale;
+			}
+		}
+
+		void IUIScrollView.ApplyContentOffset(CGPoint contentOffset, bool animated)
+		{
+			if (animated)
+			{
+				SetContentOffset(contentOffset, animated);
+			}
+			else
+			{
+				ContentOffset = contentOffset;
+			}
+		}
+
 		public MultilineTextBoxView(TextBox textBox)
 		{
 			_textBox = new WeakReference<TextBox>(textBox);