[Windows] Fix crash using complex html content (dotnet#11409)

* Fix crash using complex html content on Windows

* Use device test in all the platforms

src/Core/src/Platform/Windows/TextBlockExtensions.cs

@@ -1,7 +1,9 @@
 using System;
+using System.IO;
 using System.Text.RegularExpressions;
+using System.Xml;
 using System.Xml.Linq;
-using Microsoft.UI.Xaml;
+using System.Xml.Resolvers;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Documents;
 
@@ -111,7 +113,7 @@ internal static void UpdateTextHtml(this TextBlock platformControl, ILabel label
 
  try
  {
- var element = XElement.Parse(modifiedText);
+ var element = ParseXhtml(modifiedText);
  LabelHtmlHelper.ParseText(element, platformControl.Inlines, label);
  }
  catch (Exception)
@@ -125,5 +127,33 @@ internal static void UpdateTextPlainText(this TextBlock platformControl, IText l
  {
  platformControl.Text = label.Text;
  }
+
+ static XElement? ParseXhtml(string? html)
+ {
+ if (string.IsNullOrEmpty(html))
+ return null;
+
+ XmlNameTable nt = new NameTable();
+ XmlNamespaceManager nsmgr = new XmlNamespaceManager(nt);
+ var xmlParserContext = new XmlParserContext(null, nsmgr, null, XmlSpace.None);
+ XmlParserContext context = xmlParserContext;
+ context.DocTypeName = "html";
+ context.PublicId = "-//W3C//DTD XHTML 1.0 Strict//EN";
+ context.SystemId = "xhtml1-strict.dtd";
+ XmlParserContext xhtmlContext = context;
+
+ StringReader stringReader = new StringReader(html);
+
+ XmlReaderSettings settings = new XmlReaderSettings
+ {
+ DtdProcessing = DtdProcessing.Parse,
+ ValidationType = ValidationType.DTD,
+ XmlResolver = new XmlPreloadedResolver(XmlKnownDtds.All)
+ };
+
+ XmlReader reader = XmlReader.Create(stringReader, settings, xhtmlContext);
+
+ return XElement.Load(reader);
+ }
  }
 }

src/Core/tests/DeviceTests/Handlers/Label/LabelHandlerTests.Windows.cs

@@ -1,6 +1,4 @@
-using System;
-using System.Threading.Tasks;
-using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Media;
 
 namespace Microsoft.Maui.DeviceTests

src/Core/tests/DeviceTests/Handlers/Label/LabelHandlerTests.cs

@@ -298,6 +298,23 @@ public async Task LineHeightInitializesCorrectly()
  }
 #endif
 
+ [Fact(DisplayName = "Html Text Initializes Correctly")]
+ public async Task HtmlTextInitializesCorrectly()
+ {
+ var label = new LabelStub()
+ {
+ TextType = TextType.Html,
+ Text = "<h2><strong>Test1&nbsp;</strong>Test2</h2>"
+ };
+
+ var platformText = await GetValueAsync(label, (handler) =>
+ {
+ return handler.PlatformView.Text;
+ });
+
+ Assert.NotNull(platformText);
+ }
+
  [Category(TestCategory.Label)]
  public class LabelTextStyleTests : TextStyleHandlerTests<LabelHandler, LabelStub>
  {