fix(iOSmacOS): Obsolete the use of readonly fields

src/Uno.UI/Extensions/UIViewExtensions.iOSmacOS.cs

@@ -487,17 +487,14 @@ public static T AddTo<T>(this T thisView, _View toAddTo) where T : _View
 
 		public static void AddBorder(this _View thisButton, float borderThickness = 1, _Color borderColor = null)
 		{
+			var layer = thisButton.Layer;
 			if (borderColor != null)
 			{
-				thisButton.Layer.BorderColor = borderColor.CGColor;
+				layer.BorderColor = borderColor.CGColor;
 			}
 			if (borderThickness > 0)
 			{
-				if (Math.Abs(borderThickness - 1f) < float.Epsilon && ViewHelper.IsRetinaDisplay)
-				{
-					borderThickness = (float)ViewHelper.OnePixel;
-				}
-				thisButton.Layer.BorderWidth = borderThickness;
+				layer.BorderWidth = ViewHelper.GetConvertedPixel(borderThickness);
 			}
 		}
 

src/Uno.UI/Extensions/ViewHelper.iOSmacOS.cs

@@ -1,10 +1,12 @@
 using System;
 using System.Collections.Generic;
+using System.ComponentModel;
 using System.Drawing;
 using System.Runtime.CompilerServices;
 using Uno.UI.Extensions;
 using Uno.Foundation.Logging;
 using Uno.Extensions;
+using Windows.Graphics.Display;
 
 using Foundation;
 using CoreGraphics;
@@ -27,15 +29,23 @@ namespace Uno.UI
 	public static class ViewHelper
 	{
 #if __IOS__
+		// This return the value from the original screen. Use 'DisplayInformation.RawPixelsPerViewPixel' to get the value for the current screen.
+		[EditorBrowsable(EditorBrowsableState.Never)]
 		public static readonly nfloat MainScreenScale = UIScreen.MainScreen.Scale;
-		public static readonly bool IsRetinaDisplay = UIScreen.MainScreen.Scale > 1.0f;
+		// This return the value from the original screen. Use 'DisplayInformation.RawPixelsPerViewPixel > 1.0f' for the current screen.
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public static readonly bool IsRetinaDisplay = MainScreenScale > 1.0f;
 #elif __MACOS__
+		// This return the value from the original screen. Use 'DisplayInformation.RawPixelsPerViewPixel' to get the value for the current screen.
+		[EditorBrowsable(EditorBrowsableState.Never)]
 		public static readonly nfloat MainScreenScale = NSScreen.MainScreen.BackingScaleFactor;
-		public static readonly bool IsRetinaDisplay = NSScreen.MainScreen.BackingScaleFactor > 1.0f;
+		// This return the value from the original screen. Use 'DisplayInformation.RawPixelsPerViewPixel > 1.0f' for the current screen.
+		[EditorBrowsable(EditorBrowsableState.Never)]
+		public static readonly bool IsRetinaDisplay = MainScreenScale > 1.0f;
 #endif
 
 		private static double _rectangleRoundingEpsilon = 0.05;
-		private static double _scaledRectangleRoundingEpsilon = _rectangleRoundingEpsilon * MainScreenScale;
+		private static double _scaledRectangleRoundingEpsilon = _rectangleRoundingEpsilon * DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
 
 		/// <summary>
 		/// This is used to correct some errors when using Floor and Ceiling in LogicalToPhysicalPixels for CGRect.
@@ -46,7 +56,7 @@ public static double RectangleRoundingEpsilon
 			set
 			{
 				_rectangleRoundingEpsilon = value;
-				_scaledRectangleRoundingEpsilon = value * MainScreenScale;
+				_scaledRectangleRoundingEpsilon = value * DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
 			}
 		}
 
@@ -57,15 +67,15 @@ static ViewHelper()
 		{
 			if (typeof(ViewHelper).Log().IsEnabled(Uno.Foundation.Logging.LogLevel.Debug))
 			{
-				typeof(ViewHelper).Log().DebugFormat("Display scale is {0}", MainScreenScale);
+				typeof(ViewHelper).Log().DebugFormat("Display scale is {0}", DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel);
 			}
 		}
 
 		public static nfloat OnePixel
 		{
 			get
 			{
-				return (1.0f / MainScreenScale);
+				return (nfloat)(1.0d / DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel);
 			}
 		}
 
@@ -139,12 +149,13 @@ public static CGRect LogicalToPhysicalPixels(this CGRect size)
 			// and its size upward to the nearest whole integers, 
 			// such that the result contains the original rectangle.
 
+			var scale = DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel;
 			return new CGRect
 			(
-				(nfloat)FloorWithEpsilon(size.X * MainScreenScale) / MainScreenScale,
-				(nfloat)FloorWithEpsilon(size.Y * MainScreenScale) / MainScreenScale,
-				(nfloat)CeilingWithEpsilon(size.Width * MainScreenScale) / MainScreenScale,
-				(nfloat)CeilingWithEpsilon(size.Height * MainScreenScale) / MainScreenScale
+				(nfloat)FloorWithEpsilon(size.X * scale) / scale,
+				(nfloat)FloorWithEpsilon(size.Y * scale) / scale,
+				(nfloat)CeilingWithEpsilon(size.Width * scale) / scale,
+				(nfloat)CeilingWithEpsilon(size.Height * scale) / scale
 			);
 		}
 
@@ -182,7 +193,7 @@ private static double FloorWithEpsilon(double value)
 
 		public static nfloat GetConvertedPixel(float thickness)
 		{
-			if (IsRetinaDisplay && thickness > 0 && thickness <= 1)
+			if (thickness > 0 && thickness <= 1 && (DisplayInformation.GetForCurrentView().RawPixelsPerViewPixel > 1.0f))
 			{
 				return OnePixel;
 			}