Remove KnownColors static constructor

src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Knowncolors.cs

@@ -7,8 +7,9 @@
 #if PBTCOMPILER
 namespace MS.Internal.Markup
 #else
-using System.Collections.Generic;
 using MS.Internal;
+using System.Collections.Generic;
+using System.Globalization;
 
 namespace System.Windows.Media
 #endif
@@ -169,16 +170,6 @@ internal static class KnownColors
     {
 #if !PBTCOMPILER
 
-        static KnownColors()
-        {
-            KnownColor[] knownColorValues = Enum.GetValues<KnownColor>();
-            foreach (KnownColor colorValue in knownColorValues)
-            {
-                string aRGBString = String.Format("#{0,8:X8}", (uint)colorValue);
-                s_knownArgbColors[aRGBString] = colorValue;
-            }
-        }
-
         /// Return the solid color brush from a color string.  If there's no match, null
         public static SolidColorBrush ColorStringToKnownBrush(string s)
         {
@@ -819,20 +810,28 @@ internal static KnownColor ColorStringToKnownColor(string colorString)
 #if !PBTCOMPILER
         internal static KnownColor ArgbStringToKnownColor(string argbString)
         {
-            string argbUpper = argbString.Trim().ToUpper(System.Globalization.CultureInfo.InvariantCulture);
+            ArgumentNullException.ThrowIfNull(argbString);
+
+            ReadOnlySpan<char> argbSpan = argbString.AsSpan().Trim();
+
+            // Use NumberStyles.AllowHexSpecifier instead of NumberStyles.HexNumber because NumberStyles.HexNumber
+            // trims the whitespaces when we already trim it in the code above and we don't consider values
+            // with whitespaces between the "#" and the hex value to be valid values.
+            if (argbSpan.StartsWith('#') && uint.TryParse(argbSpan[1..], NumberStyles.AllowHexSpecifier, CultureInfo.InvariantCulture, out uint uintValue))
+            {
+                KnownColor color = (KnownColor)uintValue;
 
-            KnownColor color;
-            if (s_knownArgbColors.TryGetValue(argbUpper, out color))
-                return color;
+                if (Enum.IsDefined(color))
+                    return color;
+            }
 
-            return KnownColor.UnknownColor; 
+            return KnownColor.UnknownColor;
         }
 #if DEBUG
         private static int s_count = 0;
 #endif
 
         private static Dictionary<uint, SolidColorBrush> s_solidColorBrushCache = new Dictionary<uint, SolidColorBrush>();
-        private static Dictionary<string, KnownColor> s_knownArgbColors = new Dictionary<string, KnownColor>();
 #endif
     }
 

src/Microsoft.DotNet.Wpf/tests/UnitTests/PresentationCore.Tests/System/Windows/Media/KnownColorsTests.cs

@@ -0,0 +1,29 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Windows.Media;
+
+public sealed class KnownColorsTests
+{
+    [Theory]
+    // Supported values.
+    [InlineData(KnownColor.AliceBlue, "#FFF0F8FF")]
+    [InlineData(KnownColor.AliceBlue, " #FFF0F8FF")]
+    [InlineData(KnownColor.AliceBlue, " #FFF0F8FF ")]
+    [InlineData(KnownColor.AliceBlue, "#FFF0F8FF ")]
+    // Unsupported values.
+    [InlineData(KnownColor.UnknownColor, "")]
+    [InlineData(KnownColor.UnknownColor, " ")]
+    [InlineData(KnownColor.UnknownColor, "#020B37EF")] // Random ARGB that is not a known color.
+    [InlineData(KnownColor.UnknownColor, "# FFF0F8FF")]
+    public void ArgbStringToKnownColor_ReturnsExpected(object expected, string? argbString)
+    {
+        Assert.Equal((KnownColor)expected, KnownColors.ArgbStringToKnownColor(argbString));
+    }
+
+    [Fact]
+    public void ArgbStringToKnownColor_NullValue_ThrowsArgumentNullException()
+    {
+        Assert.Throws<ArgumentNullException>(() => KnownColors.ArgbStringToKnownColor(argbString: null));
+    }
+}