Refactor some darkmode checks.

Author: KlausLoeffelmann

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

@@ -50,7 +50,7 @@ public sealed partial class Application
 
     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
@@ -277,7 +277,14 @@ public static void SetColorMode(SystemColorMode systemColorMode)
                 return;
             }
 
-            if (GetSystemColorModeInternal() > -1)
+            if ((systemColorMode == SystemColorMode.Dark && IsSystemDarkModeAvailable)
+                || systemColorMode == SystemColorMode.Classic)
+            {
+                s_systemColorMode = systemColorMode;
+                return;
+            }
+
+            if (GetSystemColorModeInternal() > SystemDarkModeDisabled)
             {
                 s_systemColorMode = systemColorMode;
                 return;
@@ -348,43 +355,41 @@ static void NotifySystemEventsOfColorChange()
             ? SystemColorMode.Dark
             : SystemColorMode.Classic;
 
-    // Returns 0 if dark mode is available, otherwise -1 (DarkModeNotAvailable)
+    // Returns 0 if dark mode is enabled in the system, otherwise -1 (SystemDarkModeDisabled)
     private static int GetSystemColorModeInternal()
     {
-        if (SystemInformation.HighContrast)
+        if (!IsSystemDarkModeAvailable)
         {
-            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
+        {
+            systemColorMode = (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;
     }
 
+    private static bool IsSystemDarkModeAvailable =>
+        !SystemInformation.HighContrast && OsVersion.IsWindows11_OrGreater();
+
     /// <summary>
     ///  Gets a value indicating whether the application is running in a dark system color context.
     ///  Note: In a high contrast mode, this will always return <see langword="false"/>.
     /// </summary>
     [Experimental(DiagnosticIDs.ExperimentalDarkMode, UrlFormat = DiagnosticIDs.UrlFormat)]
     public static bool IsDarkModeEnabled =>
         !SystemInformation.HighContrast
-        && (SystemColorMode == SystemColorMode.Dark);
+        && (ColorMode == SystemColorMode.Dark);
 
     /// <summary>
     ///  Gets the path for the executable file that started the application.

src/System.Windows.Forms/src/System/Windows/Forms/Form.cs

@@ -4309,6 +4309,29 @@ protected override void OnHandleCreated(EventArgs e)
     {
         _formStateEx[s_formStateExUseMdiChildProc] = (IsMdiChild && Visible) ? 1 : 0;
         base.OnHandleCreated(e);
+
+        if (Properties.TryGetValue(s_propFormBorderColor, out Color? formBorderColor))
+        {
+            SetFormAttributeColorInternal(DWMWINDOWATTRIBUTE.DWMWA_BORDER_COLOR, formBorderColor.Value);
+        }
+
+        if (Properties.TryGetValue(s_propFormCaptionBackColor, out Color? formCaptionBackColor))
+        {
+            SetFormAttributeColorInternal(DWMWINDOWATTRIBUTE.DWMWA_CAPTION_COLOR, formCaptionBackColor.Value);
+        }
+
+        if (Properties.TryGetValue(s_propFormCaptionTextColor, out Color? formCaptionTextColor))
+        {
+            SetFormAttributeColorInternal(DWMWINDOWATTRIBUTE.DWMWA_TEXT_COLOR, formCaptionTextColor.Value);
+        }
+
+#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.
+        if (Properties.TryGetValue(s_propFormCornerPreference, out FormCornerPreference? cornerPreference))
+        {
+            SetFormCornerPreferenceInternal(cornerPreference.Value);
+        }
+#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.
+
         UpdateLayered();
     }
 
@@ -5912,7 +5935,7 @@ public DialogResult ShowDialog(IWin32Window? owner)
     ///   This method immediately returns, even if the form is large and takes a long time to be set up.
     ///  </para>
     ///  <para>
-    ///   If the form is already displayed asynchronously by <see cref="Form.ShowAsync"/>, an <see cref="InvalidOperationException"/> will be thrown.
+    ///   If the form is already displayed asynchronously by <see cref="ShowAsync"/>, an <see cref="InvalidOperationException"/> will be thrown.
     ///  </para>
     ///  <para>
     ///   An <see cref="InvalidOperationException"/> will also occur if no <see cref="WindowsFormsSynchronizationContext"/> could be retrieved or installed.
@@ -5947,7 +5970,7 @@ public DialogResult ShowDialog(IWin32Window? owner)
     ///   This method immediately returns, even if the form is large and takes a long time to be set up.
     ///  </para>
     ///  <para>
-    ///   If the form is already displayed asynchronously by <see cref="Form.ShowAsync"/>, an <see cref="InvalidOperationException"/> will be thrown.
+    ///   If the form is already displayed asynchronously by <see cref="ShowAsync"/>, an <see cref="InvalidOperationException"/> will be thrown.
     ///  </para>
     ///  <para>
     ///   An <see cref="InvalidOperationException"/> will also occur if no <see cref="WindowsFormsSynchronizationContext"/> could be retrieved or installed.