[RC1/9.0] Backport Dark Mode fix

src/Microsoft.VisualBasic.Forms/src/Microsoft/VisualBasic/ApplicationServices/WindowsFormsApplicationBase.vb

@@ -550,6 +550,10 @@ Namespace Microsoft.VisualBasic.ApplicationServices
             Debug.Assert(dpiSetResult, "We could net set the HighDpiMode.")
 
             ' Now, let's set VisualStyles and ColorMode:
+            If (_enableVisualStyles) Then
+                Application.EnableVisualStyles()
+            End If
+
             Application.SetColorMode(_colorMode)
 
 #Enable Warning WFO5001 ' Type is for evaluation purposes only and is subject to change or removal in future updates.

src/System.Windows.Forms/src/System/Windows/Forms/Application.cs

@@ -45,12 +45,12 @@ public sealed partial class Application
     private static bool s_useWaitCursor;
 
 #pragma warning disable WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
-    private static SystemColorMode? s_systemColorMode;
+    private static SystemColorMode? s_colorMode;
 #pragma warning restore WFO5001 // Type is for evaluation purposes only and is subject to change or removal in future updates. Suppress this diagnostic to proceed.
 
     private const string DarkModeKeyPath = "HKEY_CURRENT_USER\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize";
     private const string DarkModeKey = "AppsUseLightTheme";
-    private const int DarkModeNotAvailable = -1;
+    private const int SystemDarkModeDisabled = 1;
 
     /// <summary>
     ///  Events the user can hook into
@@ -247,27 +247,51 @@ internal static bool CustomThreadExceptionHandlerAttached
         => ThreadContext.FromCurrent().CustomThreadExceptionHandlerAttached;
 
     /// <summary>
-    ///  Gets the default dark mode for the application. This is the SystemColorMode which either has been set
-    ///  by <see cref="SetColorMode(SystemColorMode)"/> or its default value <see cref="SystemColorMode.Classic"/>.
+    ///  Gets the default color mode (dark mode) for the application.
     /// </summary>
+    /// <remarks>
+    ///  <para>
+    ///    This is the <see cref="SystemColorMode"/> which either has been set by <see cref="SetColorMode(SystemColorMode)"/>
+    ///    or its default value <see cref="SystemColorMode.Classic"/>. If it has been set to <see cref="SystemColorMode.System"/>,
+    ///    then the actual color mode is determined by the system settings (which can be retrieved by the
+    ///    static (shared in VB) <see cref="Application.SystemColorMode"/> property.
+    ///  </para>
+    /// </remarks>
     [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]
     public static SystemColorMode ColorMode =>
-        !s_systemColorMode.HasValue
-            ? SystemColorMode.Classic
-            : s_systemColorMode.Value == SystemColorMode.System
-                ? SystemColorMode
-                : s_systemColorMode.Value;
+        s_colorMode ?? SystemColorMode.Classic;
 
     /// <summary>
-    ///  Sets the default dark mode for the application.
+    ///  Sets the default color mode (dark mode) for the application.
     /// </summary>
-    /// <param name="systemColorMode">The default dark mode to set.</param>
+    /// <param name="systemColorMode">The application's default color mode (dark mode) to set.</param>
+    /// <remarks>
+    ///  <para>
+    ///    You should use this method to set the default color mode (dark mode) for the application. Set it,
+    ///    before creating any UI elements, to ensure that the correct color mode is used. You can set it to
+    ///    dark mode (<see cref="SystemColorMode.Dark"/>), light mode (<see cref="SystemColorMode.Classic"/>)
+    ///    or to the system setting (<see cref="SystemColorMode.System"/>).
+    ///  </para>
+    ///  <para>
+    ///    If you set it to <see cref="SystemColorMode.System"/>, the actual color mode is determined by the
+    ///    Windows system settings. If the system setting is changed, the application will not automatically
+    ///    adapt to the new setting.
+    ///  </para>
+    ///  <para>
+    ///    Note that the dark color mode is only available from Windows 11 on or later versions. If the system
+    ///    is set to a high contrast mode, the dark mode is not available.
+    ///  </para>
+    ///  <para>
+    ///    <b>Note for Visual Basic:</b> If you are using the Visual Basic Application Framework, you should set the
+    ///    color mode by handling the Application Events (see "WindowsFormsApplicationBase.ApplyApplicationDefaults").
+    ///  </para>
+    /// </remarks>
     [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]
     public static void SetColorMode(SystemColorMode systemColorMode)
     {
         try
         {
-            // Can't use the Generator here, since it cannot deal with experimentals.
+            // Can't use the Generator here, since it cannot deal with [Experimental].
             _ = systemColorMode switch
             {
                 SystemColorMode.Classic => systemColorMode,
@@ -276,18 +300,12 @@ public static void SetColorMode(SystemColorMode systemColorMode)
                 _ => throw new ArgumentOutOfRangeException(nameof(systemColorMode))
             };
 
-            if (systemColorMode == s_systemColorMode)
+            if (systemColorMode == s_colorMode)
             {
                 return;
             }
 
-            if (GetSystemColorModeInternal() > -1)
-            {
-                s_systemColorMode = systemColorMode;
-                return;
-            }
-
-            s_systemColorMode = SystemColorMode.Classic;
+            s_colorMode = systemColorMode;
         }
         finally
         {
@@ -315,6 +333,7 @@ static void NotifySystemEventsOfColorChange()
             bool complete = false;
             bool success = PInvoke.SendMessageCallback(hwnd, PInvoke.WM_SYSCOLORCHANGE + MessageId.WM_REFLECT, () => complete = true);
             Debug.Assert(success);
+
             if (!success)
             {
                 return;
@@ -357,25 +376,21 @@ private static int GetSystemColorModeInternal()
     {
         if (SystemInformation.HighContrast)
         {
-            return DarkModeNotAvailable;
+            return SystemDarkModeDisabled;
         }
 
-        int systemColorMode = DarkModeNotAvailable;
+        int systemColorMode = SystemDarkModeDisabled;
 
-        // Dark mode is supported when we are >= W11/22000
-        // Technically, we could go earlier, but then the APIs we're using weren't officially public.
-        if (OsVersion.IsWindows11_OrGreater())
+        try
+        {
+            // 0 for dark mode and |1| for light mode.
+            systemColorMode = Math.Abs((Registry.GetValue(
+                keyName: DarkModeKeyPath,
+                valueName: DarkModeKey,
+                defaultValue: SystemDarkModeDisabled) as int?) ?? systemColorMode);
+        }
+        catch (Exception ex) when (!ex.IsCriticalException())
         {
-            try
-            {
-                systemColorMode = (Registry.GetValue(
-                    keyName: DarkModeKeyPath,
-                    valueName: DarkModeKey,
-                    defaultValue: DarkModeNotAvailable) as int?) ?? systemColorMode;
-            }
-            catch (Exception ex) when (!ex.IsCriticalException())
-            {
-            }
         }
 
         return systemColorMode;
@@ -388,7 +403,8 @@ private static int GetSystemColorModeInternal()
     [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]
     public static bool IsDarkModeEnabled =>
         !SystemInformation.HighContrast
-        && (ColorMode == SystemColorMode.Dark);
+        && (ColorMode == SystemColorMode.Dark
+            || (ColorMode == SystemColorMode.System && SystemColorMode == SystemColorMode.Dark));
 
     /// <summary>
     ///  Gets the path for the executable file that started the application.