[Android] System Fonts fix (#20961)

* Added a UI test (#19556)

* [Android] Systemfonts fix (#19556)

* Code review comments

* [android] Add screenshot for UI test

---------

Co-authored-by: Rui Marinho <me@ruimarinho.net>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue19556.xaml

@@ -0,0 +1,42 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue19556"
+             xmlns:ios="clr-namespace:Microsoft.Maui.Controls.PlatformConfiguration.iOSSpecific;assembly=Microsoft.Maui.Controls"
+             ios:NavigationPage.PrefersLargeTitles="false"
+             Title="Issue19556">
+    <StackLayout Padding="30,0" Spacing="0">
+        <Label Text="NET Multi-platform App UI monospace"
+                FontFamily="monospace"
+                AutomationId="label"
+                SemanticProperties.HeadingLevel="Level1" />
+        <Label Text=".NET Multi-platform App UI sans-serif-condensed"
+                FontFamily="sans-serif-condensed"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif-condensed" />
+        <Label Text=".NET Multi-platform App UI sans-serif-condensed-light"
+                FontFamily="sans-serif-condensed-light"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif-condensed-light" />
+        <Label Text=".NET Multi-platform App UI serif"
+                FontFamily="serif"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I serif " />
+        <Label Text=".NET Multi-platform App UI sans-serif"
+                FontFamily="sans-serif"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif" />
+        <Label Text=".NET Multi-platform App UI sans-serif-black"
+                FontFamily="sans-serif-black"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif-black" />
+        <Label Text=".NET Multi-platform App UI sans-serif-light"
+                FontFamily="sans-serif-light"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif-light" />
+        <Label Text=".NET Multi-platform App UI sans-serif-medium"
+                FontFamily="sans-serif-medium"
+                SemanticProperties.HeadingLevel="Level2"
+                SemanticProperties.Description="Welcome to dot net Multi platform App U I sans-serif-medium" />
+    </StackLayout>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue19556.xaml.cs

@@ -0,0 +1,14 @@
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+namespace Maui.Controls.Sample.Issues;
+
+[XamlCompilation(XamlCompilationOptions.Compile)]
+[Issue(IssueTracker.Github, 19556, "[Android] Systemfonts (light/black etc.) not working", PlatformAffected.Android)]
+
+public partial class Issue19556 : ContentPage
+{
+	public Issue19556()
+	{
+		InitializeComponent();
+	}
+}

src/Controls/tests/UITests/Tests/Issues/Issue19556.cs

@@ -0,0 +1,25 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues;
+
+public class Issue19556 : _IssuesUITest
+{
+	public override string Issue => "[Android] Systemfonts (light/black etc.) not working";
+
+	public Issue19556(TestDevice device)
+		: base(device)
+	{ }
+
+    [Test]
+	public void SystemFontsShouldRenderCorrectly()
+	{
+		this.IgnoreIfPlatforms(new TestDevice[] { TestDevice.iOS, TestDevice.Mac, TestDevice.Windows });
+
+		_ = App.WaitForElement("label");
+
+		// The test passes if fonts are correctly rendered
+		VerifyScreenshot();
+	}
+}

src/Core/src/Fonts/FontManager.Android.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.IO;
 using Android.Graphics;
 using Android.Graphics.Fonts;
@@ -18,6 +19,14 @@ public class FontManager : IFontManager
 			"fonts/",
 		};
 
+		static readonly Dictionary<string, FontWeight> FontWeightMap = new(StringComparer.OrdinalIgnoreCase)
+		{
+			{ "-light", FontWeight.Light },
+			{ "-medium", FontWeight.Medium },
+			{ "-black", FontWeight.Black }
+			// Add more styles as needed
+		};
+
 		readonly ConcurrentDictionary<(string? fontFamilyName, FontWeight weight, bool italic), Typeface?> _typefaces = new();
 		readonly IFontRegistrar _fontRegistrar;
 		readonly IServiceProvider? _serviceProvider;
@@ -171,7 +180,20 @@ public FontSize GetFontSize(Font font, float defaultFontSize = 0)
 			}
 
 			if (OperatingSystem.IsAndroidVersionAtLeast(28))
+			{
+				if (!string.IsNullOrWhiteSpace(fontFamily))
+				{
+					foreach (var fontWeight in FontWeightMap)
+					{
+						if (fontFamily.EndsWith(fontWeight.Key, StringComparison.OrdinalIgnoreCase))
+						{
+							return Typeface.Create(result, (int)fontWeight.Value, italic);
+						}
+					}
+				}
+
 				result = Typeface.Create(result, (int)weight, italic);
+			}
 			else
 				result = Typeface.Create(result, style);