[iOS] Fixed updating Label TextDecorations when no Text is set

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5003.xaml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:local="clr-namespace:Xamarin.Forms.Controls.Issues"
+             x:Class="Xamarin.Forms.Controls.Issues.Issue5003">
+    <ContentPage.Resources>
+        <ResourceDictionary>
+            <local:StrikeThroughIfTrueConverter x:Key="StrikeThroughIfTrueConverter"/>
+        </ResourceDictionary>
+    </ContentPage.Resources>
+    <ContentPage.Content>
+    <Label  Text="{Binding MyNullString}" 
+                TextDecorations="{Binding SomeBoolean, Converter={StaticResource StrikeThroughIfTrueConverter}}"/>
+    </ContentPage.Content>
+</ContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue5003.xaml.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Globalization;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+namespace Xamarin.Forms.Controls.Issues
+{
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 5003, "iOS StrikeThrough applied to null string throws error", PlatformAffected.iOS)]
+	public partial class Issue5003 : ContentPage
+	{
+
+		public Issue5003()
+		{
+#if APP
+			InitializeComponent();
+#endif
+			BindingContext = new VM();
+		}
+
+		[Preserve(AllMembers = true)]
+		class VM
+		{
+			public string MyNullString { get; set; }
+			public bool SomeBoolean { get; set; }
+		}
+	}
+
+	public class StrikeThroughIfTrueConverter : IValueConverter
+	{
+		public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+		{
+			if (value is bool b)
+			{
+				if (b)
+					return TextDecorations.Strikethrough;
+			}
+
+			return TextDecorations.None;
+		}
+
+		public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+		{
+			throw new NotImplementedException();
+		}
+	}
+}

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

@@ -427,6 +427,10 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)Issue4600.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Issue5003.xaml.cs">
+      <DependentUpon>Issue5003.xaml</DependentUpon>
+      <SubType>Code</SubType>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)LegacyComponents\NonAppCompatSwitch.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)MapsModalCrash.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ModalActivityIndicatorTest.cs" />
@@ -1089,4 +1093,10 @@
       <Generator>MSBuild:UpdateDesignTimeXaml</Generator>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue5003.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

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

@@ -133,7 +133,7 @@ protected override void Dispose(bool disposing)
 			base.Dispose(disposing);
 			if (disposing)
 			{
-				if(Element != null)
+				if (Element != null)
 				{
 					Element.PropertyChanging -= ElementPropertyChanging;
 				}
@@ -216,6 +216,14 @@ void UpdateTextDecorations()
 			if (!Element.IsSet(Label.TextDecorationsProperty))
 				return;
 
+#if __MOBILE__
+			if (!(Control.AttributedText?.Length > 0))
+				return;
+#else
+			if (!(Control.AttributedStringValue?.Length > 0))
+				return;
+#endif
+
 			var textDecorations = Element.TextDecorations;
 #if __MOBILE__
 			var newAttributedText = new NSMutableAttributedString(Control.AttributedText);