[iOS] Label HorizontalTextAlignment="Center" not working in conjunction with LineHeight on iOS (#4275)

* fix issue#4262
Label HorizontalTextAlignment="Center" not working in conjunction with LineHeight on iOS

* Add missing parameter for macOS due to the previous method param change

* merge

* Added using UITextAlignment = AppKit.NSTextAlignment; as maintainability requested

* Revert "merge"

This reverts commit 939b6e1bc8ebd538af0db91dd8656e7eb2d31203.

* Revert "merge"

This reverts commit 939b6e1bc8ebd538af0db91dd8656e7eb2d31203.

* make test case more clear

Xamarin.Forms.Build

@@ -1 +1 @@
-Subproject commit dcf2726eac6b47c64555ddb19966aa40ef31d1fa
+Subproject commit 8f864cf6b0c9e7b1973bee04e5fd81933067163e

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue4262.cs

@@ -0,0 +1,22 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 4262, "Label HorizontalTextAlignment=\"Center\" not working in conjunction with LineHeight on iOS", PlatformAffected.iOS)]
+	public class Issue4262 : ContentPage
+	{
+		public Issue4262()
+		{
+			var label = new Label() { Text = "This is center aligned
line 2.", HorizontalTextAlignment = TextAlignment.Center };
+			var label2 = new Label() { Text = "If this is not center aligned, this test has failed.", HorizontalTextAlignment = TextAlignment.Center, LineHeight = 1.5 };
+
+			Content = new StackLayout()
+			{
+				Children = { label, label2 },
+				VerticalOptions = LayoutOptions.CenterAndExpand
+			};
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -406,6 +406,7 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue4136.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue4262.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)LegacyComponents\NonAppCompatSwitch.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)MapsModalCrash.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ModalActivityIndicatorTest.cs" />

Xamarin.Forms.Platform.iOS/Renderers/FormattedStringExtensions.cs

@@ -8,7 +8,7 @@ namespace Xamarin.Forms.Platform.iOS
 #else
 using AppKit;
 using UIColor = AppKit.NSColor;
-
+using UITextAlignment = AppKit.NSTextAlignment;
 namespace Xamarin.Forms.Platform.MacOS
 #endif
 {
@@ -53,8 +53,8 @@ namespace Xamarin.Forms.Platform.MacOS
 
 			return attributed;
 		}
-
-		internal static NSAttributedString ToAttributed(this Span span, Element owner, Color defaultForegroundColor, double lineHeight = -1.0)
+		
+		internal static NSAttributedString ToAttributed(this Span span, Element owner, Color defaultForegroundColor, TextAlignment textAlignment, double lineHeight = -1.0)
 		{
 			if (span == null)
 				return null;
@@ -63,14 +63,30 @@ namespace Xamarin.Forms.Platform.MacOS
 			if (text == null)
 				return null;
 
-			NSMutableParagraphStyle style = null;
+			NSMutableParagraphStyle style = new NSMutableParagraphStyle();
 			lineHeight = span.LineHeight >= 0 ? span.LineHeight : lineHeight;
 			if (lineHeight >= 0)
 			{
-				style = new NSMutableParagraphStyle();
 				style.LineHeightMultiple = new nfloat(lineHeight);
 			}
 
+			switch (textAlignment)
+			{
+				case TextAlignment.Start:
+					style.Alignment = UITextAlignment.Left;
+					break;
+				case TextAlignment.Center:
+					style.Alignment = UITextAlignment.Center;
+					break;
+				case TextAlignment.End:
+					style.Alignment = UITextAlignment.Right;
+					break;
+				default:
+					style.Alignment = UITextAlignment.Left;
+					break;
+			}
+
+
 #if __MOBILE__
 			UIFont targetFont;
 			if (span.IsDefault())
@@ -120,7 +136,7 @@ namespace Xamarin.Forms.Platform.MacOS
 		}
 
 		internal static NSAttributedString ToAttributed(this FormattedString formattedString, Element owner,
-			Color defaultForegroundColor, double lineHeight = -1.0)
+			Color defaultForegroundColor, TextAlignment textAlignment = TextAlignment.Start, double lineHeight = -1.0)
 		{
 			if (formattedString == null)
 				return null;
@@ -129,7 +145,9 @@ namespace Xamarin.Forms.Platform.MacOS
 			for (int i = 0; i < formattedString.Spans.Count; i++)
 			{
 				Span span = formattedString.Spans[i];
-				var attributedString = span.ToAttributed(owner, defaultForegroundColor, lineHeight);
+
+				var attributedString = span.ToAttributed(owner, defaultForegroundColor, textAlignment, lineHeight);
+
 				if (attributedString == null)
 					continue;
 

Xamarin.Forms.Platform.iOS/Renderers/LabelRenderer.cs

@@ -328,9 +328,9 @@ namespace Xamarin.Forms.Platform.MacOS
 		void UpdateFormattedText()
 		{
 #if __MOBILE__
-			Control.AttributedText = _formatted.ToAttributed(Element, Element.TextColor, Element.LineHeight);
+			Control.AttributedText = _formatted.ToAttributed(Element, Element.TextColor, Element.HorizontalTextAlignment, Element.LineHeight);
 #else
-			Control.AttributedStringValue = _formatted.ToAttributed(Element, Element.TextColor, Element.LineHeight);
+			Control.AttributedStringValue = _formatted.ToAttributed(Element, Element.TextColor, Element.HorizontalTextAlignment, Element.LineHeight);
 #endif
 		}