Using reflection to add handler for user preference events (dotnet/co…

…refx#37853)

* using reflection to add handler for user preference events

* adding comments, correcting typo and using GetType

* adding debug.asserts

* pushing down color translator

* using open unbound delegate pointing directly to getter method of the eventargs category property

* No longer using colorTable on netcoreapp 2.1 in system.Drawing.Common

* reverting the use of extension method.

* doing  s_color check first and adding null check for category getter

* missing semicolon

* improving comments and adding tests

* removing extra using

* using already defined known color

* skipping the test on nano and non-windows platform

* introducing a custom property


Commit migrated from dotnet/corefx@d24b3e3

src/libraries/Common/src/System/Drawing/KnownColorTable.cs

@@ -3,16 +3,13 @@
 // See the LICENSE file in the project root for more information.
 
 using System.Diagnostics;
+using System.Reflection;
 
 namespace System.Drawing
 {
-#if FEATURE_SYSTEM_EVENTS
-    using Microsoft.Win32;
-    using System.Drawing.Internal;
-#endif
-
     static internal class KnownColorTable
     {
+        private static Func<EventArgs, int> s_categoryGetter;
         private static int[] s_colorTable;
         private static string[] s_colorNameTable;
 
@@ -59,9 +56,48 @@ private static void InitColorTable()
         {
             int[] values = new int[(unchecked((int)KnownColor.MenuHighlight)) + 1];
 
-#if FEATURE_SYSTEM_EVENTS
-            SystemEvents.UserPreferenceChanging += new UserPreferenceChangingEventHandler(OnUserPreferenceChanging);
-#endif
+            // When Microsoft.Win32.SystemEvents is available, we can react to the UserPreferenceChanging events by updating
+            // SystemColors. In order to avoid a static dependency on SystemEvents since it is not available on all platforms 
+            // and as such we don't want to bring it into the shared framework. We use the desktop identity for SystemEvents
+            // since it is stable and will remain stable for compatibility whereas the core identity could change.
+            Type systemEventsType = Type.GetType("Microsoft.Win32.SystemEvents, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", throwOnError: false);
+            EventInfo upEventInfo = systemEventsType?.GetEvent("UserPreferenceChanging", BindingFlags.Public | BindingFlags.Static);
+
+            if (upEventInfo != null)
+            {
+                // Delegate TargetType
+                Type userPrefChangingDelegateType = Type.GetType("Microsoft.Win32.UserPreferenceChangingEventHandler, System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089", throwOnError: false);
+                Debug.Assert(userPrefChangingDelegateType != null);
+
+                if (userPrefChangingDelegateType != null)
+                {
+                    // we are using MethodInfo overload because it allows relaxed signature binding i.e. the types dont need to be exact match. It allows base classes as well.
+                    MethodInfo mi = typeof(KnownColorTable).GetMethod(nameof(OnUserPreferenceChanging), BindingFlags.NonPublic | BindingFlags.Static);
+                    Debug.Assert(mi != null);
+
+                    if (mi != null)
+                    {
+                        // Creating a delegate to use it as event handler.
+                        Delegate handler = Delegate.CreateDelegate(userPrefChangingDelegateType, mi);
+                        upEventInfo.AddEventHandler(null, handler);
+                    }
+
+                    // Retrieving getter of the category property of the UserPreferenceChangingEventArgs.
+                    Type argsType = Type.GetType("Microsoft.Win32.UserPreferenceChangingEventArgs, System, Version = 4.0.0.0, Culture = neutral, PublicKeyToken = b77a5c561934e089", throwOnError: false);
+                    PropertyInfo categoryProperty = argsType?.GetProperty("Category", BindingFlags.Instance | BindingFlags.Public);
+                    MethodInfo categoryGetter = categoryProperty?.GetGetMethod();
+
+                    Debug.Assert(categoryGetter != null);
+                    if (categoryGetter != null)
+                    {
+                        // Creating a Delegate pointing to the getter method. 
+                        s_categoryGetter = (Func<EventArgs, int>)typeof(KnownColorTable).GetMethod(nameof(CreateGetter), BindingFlags.NonPublic | BindingFlags.Static)
+                            .MakeGenericMethod(argsType, categoryGetter.ReturnType)
+                            .Invoke(null, new object[] { categoryGetter });
+                    }
+                }
+            }
+
             UpdateSystemColors(values);
 
             // just consts...
@@ -210,6 +246,15 @@ private static void InitColorTable()
             s_colorTable = values;
         }
 
+        // Generic method that we specialize at runtime once we've loaded the UserPreferenceChangingEventArgs type.
+        // It permits creating an unbound delegate so that we can avoid reflection after the initial
+        // lightup code completes.
+        private static Func<EventArgs, int> CreateGetter<TInstance, TProperty>(MethodInfo method) where TInstance : EventArgs where TProperty : Enum
+        {
+            Func<TInstance, TProperty> typedDelegate = (Func<TInstance, TProperty>)Delegate.CreateDelegate(typeof(Func<TInstance, TProperty>), null, method);
+            return (EventArgs instance) => (int)(object)typedDelegate((TInstance)instance);
+        }
+
         private static void EnsureColorNameTable()
         {
             // no need to lock... worse case is a double create of the table...
@@ -438,15 +483,15 @@ private static int FromWin32Value(int value)
         }
 #endif
 
-#if FEATURE_SYSTEM_EVENTS
-        private static void OnUserPreferenceChanging(object sender, UserPreferenceChangingEventArgs e)
+        private static void OnUserPreferenceChanging(object sender, EventArgs args)
         {
-            if (e.Category == UserPreferenceCategory.Color && s_colorTable != null)
+            Debug.Assert(s_categoryGetter != null);
+            // Access UserPreferenceChangingEventArgs.Category value through cached delegate.
+            if (s_colorTable != null && s_categoryGetter != null && s_categoryGetter(args) == 2) // UserPreferenceCategory.Color = 2
             {
                 UpdateSystemColors(s_colorTable);
             }
         }
-#endif
 
         private static void UpdateSystemColors(int[] colorTable)
         {

src/libraries/System.Drawing.Common/ref/System.Drawing.Common.Forwards.cs

@@ -2,4 +2,5 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Drawing.SystemColors))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Drawing.SystemColors))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Drawing.ColorTranslator))]

src/libraries/System.Drawing.Common/ref/System.Drawing.Common.cs

@@ -238,15 +238,6 @@ public partial struct CharacterRange
         public static bool operator ==(System.Drawing.CharacterRange cr1, System.Drawing.CharacterRange cr2) { throw null; }
         public static bool operator !=(System.Drawing.CharacterRange cr1, System.Drawing.CharacterRange cr2) { throw null; }
     }
-    public static partial class ColorTranslator
-    {
-        public static System.Drawing.Color FromHtml(string htmlColor) { throw null; }
-        public static System.Drawing.Color FromOle(int oleColor) { throw null; }
-        public static System.Drawing.Color FromWin32(int win32Color) { throw null; }
-        public static string ToHtml(System.Drawing.Color c) { throw null; }
-        public static int ToOle(System.Drawing.Color c) { throw null; }
-        public static int ToWin32(System.Drawing.Color c) { throw null; }
-    }
     public enum ContentAlignment
     {
         TopLeft = 1,

src/libraries/System.Drawing.Common/ref/System.Drawing.Common.netstandard.cs

@@ -3,7 +3,16 @@
 // See the LICENSE file in the project root for more information.
 
 namespace System.Drawing
-{    
+{
+    public static partial class ColorTranslator
+    {
+        public static System.Drawing.Color FromHtml(string htmlColor) { throw null; }
+        public static System.Drawing.Color FromOle(int oleColor) { throw null; }
+        public static System.Drawing.Color FromWin32(int win32Color) { throw null; }
+        public static string ToHtml(System.Drawing.Color c) { throw null; }
+        public static int ToOle(System.Drawing.Color c) { throw null; }
+        public static int ToWin32(System.Drawing.Color c) { throw null; }
+    }
     public static partial class SystemColors
     {
         public static System.Drawing.Color ActiveBorder { get { throw null; } }

src/libraries/System.Drawing.Common/src/System.Drawing.Common.csproj

@@ -20,7 +20,6 @@
     <Compile Include="System\Drawing\BufferedGraphicsContext.cs" />
     <Compile Include="System\Drawing\Brushes.cs" />
     <Compile Include="System\Drawing\CharacterRange.cs" />
-    <Compile Include="System\Drawing\ColorTranslator.cs" />
     <Compile Include="System\Drawing\ContentAlignment.cs" />
     <Compile Include="System\Drawing\IDeviceContext.cs" />
     <Compile Include="System\Drawing\GdiplusNative.cs" />
@@ -154,19 +153,22 @@
     <Compile Include="System\Drawing\Imaging\ImageCodecInfo.cs" />
     <Compile Include="System\Drawing\Imaging\ImageCodecInfoPrivate.cs" />
     <Compile Include="System\Drawing\Imaging\MetafileFrameUnit.cs" />
-    <Compile Include="$(CommonPath)\System\Drawing\ColorConverterCommon.cs">
+    <Compile Condition="'$(TargetGroup)' == 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\ColorConverterCommon.cs">
       <Link>System\Drawing\ColorConverterCommon.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)\System\Drawing\ColorTable.cs">
+    <Compile Condition="'$(TargetGroup)' == 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\ColorTable.cs">
       <Link>System\Drawing\ColorTable.cs</Link>
     </Compile>
+    <Compile Condition="'$(TargetGroup)' == 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\ColorTranslator.cs">
+      <Link>System\Drawing\ColorTranslator.cs</Link>
+    </Compile>
     <Compile Condition="'$(TargetGroup)' == 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\ColorUtil.netcoreapp20.cs">
       <Link>System\Drawing\ColorUtil.netcoreapp20.cs</Link>
     </Compile>
     <Compile Condition="'$(TargetGroup)' != 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\ColorUtil.netcoreapp21.cs">
       <Link>System\Drawing\ColorUtil.netcoreapp21.cs</Link>
     </Compile>
-    <Compile Include="$(CommonPath)\System\Drawing\KnownColorTable.cs">
+    <Compile Condition="'$(TargetGroup)' == 'netcoreapp2.0'" Include="$(CommonPath)\System\Drawing\KnownColorTable.cs">
       <Link>System\Drawing\KnownColorTable.cs</Link>
     </Compile>
     <Compile Include="$(CommonPath)\System\Runtime\InteropServices\FunctionWrapper.cs">

src/libraries/System.Drawing.Primitives/ref/System.Drawing.Primitives.cs

@@ -180,6 +180,15 @@ namespace System.Drawing
         public System.Drawing.KnownColor ToKnownColor() { throw null; }
         public override string ToString() { throw null; }
     }
+    public static partial class ColorTranslator
+    {
+        public static System.Drawing.Color FromHtml(string htmlColor) { throw null; }
+        public static System.Drawing.Color FromOle(int oleColor) { throw null; }
+        public static System.Drawing.Color FromWin32(int win32Color) { throw null; }
+        public static string ToHtml(System.Drawing.Color c) { throw null; }
+        public static int ToOle(System.Drawing.Color c) { throw null; }
+        public static int ToWin32(System.Drawing.Color c) { throw null; }
+    }
     public enum KnownColor
     {
         ActiveBorder = 1,

src/libraries/System.Drawing.Primitives/src/Resources/Strings.resx

@@ -57,6 +57,12 @@
   <resheader name="writer">
     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
+  <data name="ConvertInvalidPrimitive" xml:space="preserve">
+    <value>{0} is not a valid value for {1}.</value>
+  </data>
+  <data name="InvalidColor" xml:space="preserve">
+    <value>Color '{0}' is not valid.</value>
+  </data>
   <data name="InvalidEx2BoundArgument" xml:space="preserve">
     <value>Value of '{1}' is not valid for '{0}'. '{0}' should be greater than or equal to {2} and less than or equal to {3}.</value>
   </data>

src/libraries/System.Drawing.Primitives/src/System.Drawing.Primitives.csproj

@@ -25,9 +25,15 @@
     <Compile Include="System\Drawing\Size.cs" />
     <Compile Include="System\Drawing\SizeF.cs" />
     <Compile Include="System\Drawing\Color.cs" />
+    <Compile Include="$(CommonPath)\System\Drawing\ColorConverterCommon.cs">
+      <Link>System\Drawing\ColorConverterCommon.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)\System\Drawing\ColorTable.cs">
       <Link>System\Drawing\ColorTable.cs</Link>
     </Compile>
+    <Compile Include="$(CommonPath)\System\Drawing\ColorTranslator.cs">
+      <Link>System\Drawing\ColorTranslator.cs</Link>
+    </Compile>
     <Compile Include="$(CommonPath)\System\Drawing\ColorUtil.netcoreapp21.cs">
       <Link>System\Drawing\ColorUtil.netcoreapp21.cs</Link>
     </Compile>

src/libraries/System.Drawing.Primitives/tests/ColorTests.cs

@@ -5,12 +5,15 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.Drawing.Primitives.Tests
 {
     public partial class ColorTests
     {
+        public static bool SupportsSystemEvents => PlatformDetection.IsWindows && !PlatformDetection.IsUap && PlatformDetection.IsNotWindowsNanoServer;
+
         public static readonly IEnumerable<object[]> NamedArgbValues =
             new[]
             {
@@ -491,5 +494,45 @@ public void DebuggerAttributesAreValid()
             DebuggerAttributes.ValidateDebuggerDisplayReferences(Color.Aquamarine);
             DebuggerAttributes.ValidateDebuggerDisplayReferences(Color.FromArgb(4, 3, 2, 1));
         }
+
+        [ConditionalFact(nameof(SupportsSystemEvents))]
+        public void UserPreferenceChangingEventTest()
+        {
+            int element = 12; // Win32SystemColors.AppWorkSpace.
+            Color oldColor = System.Drawing.SystemColors.AppWorkspace;
+
+            // A call to ToArgb is necessary before changing the system colors because it initializes the knownColorTable.
+            int oldColorArgb = oldColor.ToArgb();
+            int oldColorAbgr = GetColorRefValue(oldColor);
+
+            Color newColor = oldColor != Color.Gold ? Color.Gold : Color.Silver;
+            int newColorArgb = newColor.ToArgb();
+            int newColorAbgr = GetColorRefValue(newColor);
+
+            Assert.NotEqual(newColorArgb, oldColorArgb);
+
+            try
+            {
+                Assert.Equal(1, SetSysColors(1, new int[] { element }, new int[] { newColorAbgr }));
+
+                RetryHelper.Execute(() =>
+                {
+                    Assert.Equal(newColorArgb, oldColor.ToArgb());
+                });
+            }
+            finally
+            {
+                Assert.Equal(1, SetSysColors(1, new int[] { element }, new int[] { oldColorAbgr }));
+            }
+        }
+
+        [DllImport("user32.dll", SetLastError = true)]
+        private static extern int SetSysColors(int cElements, int[] lpaElements, int[] lpaRgbValues);
+
+        private static int GetColorRefValue(Color color)
+        {
+            // The COLORREF value has the following hexadecimal form: 0x00bbggrr.
+            return color.B << 16 | color.G << 8 | color.R;
+        }
     }
 }