Darken TabControl in dark mode

Author: willibrandon

src/System.Windows.Forms/System/Windows/Forms/Control.cs

@@ -162,6 +162,7 @@ public unsafe partial class Control :
     internal const string ExplorerThemeIdentifier = "Explorer";
     internal const string ItemsViewThemeIdentifier = "ItemsView";
     internal const string ComboBoxButtonThemeIdentifier = "CFD";
+    internal const string BannerContainerThemeIdentifier = "FileExplorerBannerContainer";
 
     private const short PaintLayerBackground = 1;
     private const short PaintLayerForeground = 2;
@@ -9207,9 +9208,12 @@ internal virtual void RecreateHandleCore()
 
             bool focused = ContainsFocus;
 
-            Debug.WriteLineIf(CoreSwitches.PerfTrack.Enabled, $"RecreateHandle: {GetType().FullName} [Text={Text}]");
+            Debug.WriteLineIf(
+                CoreSwitches.PerfTrack.Enabled,
+                $"RecreateHandle: {GetType().FullName} [Text={Text}]");
 
             bool created = GetState(States.Created);
+
             if (GetState(States.TrackingMouseEvent))
             {
                 SetState(States.MouseEnterPending, true);
@@ -9232,9 +9236,11 @@ internal virtual void RecreateHandleCore()
                 if (ChildControls is { } children && children.Count > 0)
                 {
                     controlSnapshot = new Control[children.Count];
+
                     for (int i = 0; i < children.Count; i++)
                     {
                         Control childControl = children[i];
+
                         if (childControl is not null && childControl.IsHandleCreated)
                         {
                             // SetParent to parking window
@@ -9294,6 +9300,7 @@ internal virtual void RecreateHandleCore()
                     for (int i = 0; i < controlSnapshot.Length; i++)
                     {
                         Control? childControl = controlSnapshot[i];
+
                         if (childControl is not null && childControl.IsHandleCreated)
                         {
                             // Re-parent the control.

src/System.Windows.Forms/System/Windows/Forms/Controls/TabControl/TabControl.cs

@@ -72,6 +72,7 @@ public partial class TabControl : Control
     private bool _skipUpdateSize;
 
     private ToolTipBuffer _toolTipBuffer;
+    private bool _suspendDarkModeChange;
 
     /// <summary>
     ///  Constructs a TabBase object, usually as the base class for a TabStrip or TabControl.
@@ -154,7 +155,10 @@ public TabAppearance Appearance
                 SourceGenerated.EnumValidator.Validate(value);
 
                 _appearance = value;
+
+                _suspendDarkModeChange = true;
                 RecreateHandle();
+                ApplyDarkModeOnDemand();
 
                 // Fire OnStyleChanged(EventArgs.Empty) here since we are no longer calling UpdateStyles( ) but always reCreating the Handle.
                 OnStyleChanged(EventArgs.Empty);
@@ -1245,6 +1249,7 @@ protected override void OnHandleCreated(EventArgs e)
         base.OnHandleCreated(e);
         _cachedDisplayRect = Rectangle.Empty;
         ApplyItemSize();
+
         if (_imageList is not null)
         {
             PInvokeCore.SendMessage(this, PInvoke.TCM_SETIMAGELIST, 0, _imageList.Handle);
@@ -1290,7 +1295,22 @@ protected override void OnHandleCreated(EventArgs e)
         }
 
         UpdateTabSelection(false);
+        ApplyDarkModeOnDemand();
+    }
+
+#pragma warning disable WFO5001
+    private void ApplyDarkModeOnDemand()
+    {
+        // We need to avoid to apply the DarkMode theme twice on handle recreate.
+        if (!_suspendDarkModeChange && Application.IsDarkModeEnabled)
+        {
+            PInvoke.SetWindowTheme(HWND, null, $"{DarkModeIdentifier}::{BannerContainerThemeIdentifier}");
+            PInvokeCore.EnumChildWindows(this, StyleChildren);
+        }
+
+        _suspendDarkModeChange = false;
     }
+#pragma warning restore WFO5001
 
     protected override void OnHandleDestroyed(EventArgs e)
     {
@@ -1554,6 +1574,8 @@ internal override void RecreateHandleCore()
             TabPages.Add(tabPages[i]);
         }
 
+        ApplyDarkModeOnDemand();
+
         try
         {
             SetState(State.FromCreateHandles, true);
@@ -1772,6 +1794,10 @@ private bool ShouldSerializeItemSize()
         return !_padding.Equals(s_defaultPaddingPoint);
     }
 
+    private BOOL StyleChildren(HWND handle) =>
+        PInvoke.SetWindowTheme(handle, $"{DarkModeIdentifier}_{ExplorerThemeIdentifier}", null)
+            .Succeeded;
+
     /// <summary>
     ///  Returns a string representation for this control.
     /// </summary>
@@ -1809,6 +1835,7 @@ protected void UpdateTabSelection(bool updateFocus)
 
             // make current panel invisible
             TabPage[] tabPages = GetTabPages();
+
             if (index != -1)
             {
                 // Changing the bounds of the TabPage during scaling
@@ -1890,6 +1917,7 @@ protected override void OnStyleChanged(EventArgs e)
     {
         base.OnStyleChanged(e);
         _cachedDisplayRect = Rectangle.Empty;
+
         UpdateTabSelection(false);
     }