Fix disabled ComboBox BackColor issue.

Fix disabled RichTextBox BackColor issue.

Author: KlausLoeffelmann

src/System.Windows.Forms/PublicAPI.Unshipped.txt

@@ -1,2 +0,0 @@
-override System.Windows.Forms.ComboBox.OnEnabledChanged(System.EventArgs! e) -> void
-override System.Windows.Forms.RichTextBox.OnEnabledChanged(System.EventArgs! e) -> void

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

@@ -1857,11 +1857,8 @@ protected override void Dispose(bool disposing)
                 _autoCompleteCustomSource.CollectionChanged -= OnAutoCompleteCustomSourceChanged;
             }
 
-            if (_stringSource is not null)
-            {
-                _stringSource.ReleaseAutoComplete();
-                _stringSource = null;
-            }
+            _stringSource?.ReleaseAutoComplete();
+            _stringSource = null;
         }
 
         base.Dispose(disposing);
@@ -2400,11 +2397,8 @@ protected override void OnHandleDestroyed(EventArgs e)
             _selectedIndex = SelectedIndex;
         }
 
-        if (_stringSource is not null)
-        {
-            _stringSource.ReleaseAutoComplete();
-            _stringSource = null;
-        }
+        _stringSource?.ReleaseAutoComplete();
+        _stringSource = null;
 
         base.OnHandleDestroyed(e);
     }
@@ -3058,23 +3052,14 @@ protected override void RefreshItem(int index)
     /// </summary>
     private void ReleaseChildWindow()
     {
-        if (_childEdit is not null)
-        {
-            _childEdit.ReleaseHandle();
-            _childEdit = null;
-        }
+        _childEdit?.ReleaseHandle();
+        _childEdit = null;
 
-        if (_childListBox is not null)
-        {
-            _childListBox.ReleaseHandle();
-            _childListBox = null;
-        }
+        _childListBox?.ReleaseHandle();
+        _childListBox = null;
 
-        if (_childDropDown is not null)
-        {
-            _childDropDown.ReleaseHandle();
-            _childDropDown = null;
-        }
+        _childDropDown?.ReleaseHandle();
+        _childDropDown = null;
     }
 
     internal override void ReleaseUiaProvider(HWND handle)
@@ -3692,13 +3677,11 @@ protected override unsafe void WndProc(ref Message m)
 
                 break;
 
-            case PInvokeCore.WM_CTLCOLOREDIT:
-                // Only handle if the ComboBox is disabled
-#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 (IsHandleCreated
-                    && !Enabled
-                    && Application.IsDarkModeEnabled
-                    && DarkModeRequestState is true)
+#pragma warning disable WFO5001
+            case PInvokeCore.WM_CTLCOLORSTATIC:
+
+                HWND hwndChild = (HWND)m.LParamInternal;
+                if (hwndChild == _childEdit?.HWND && Application.IsDarkModeEnabled)
                 {
                     PInvokeCore.SetBkColor(
                         (HDC)m.WParamInternal,
@@ -3709,14 +3692,31 @@ protected override unsafe void WndProc(ref Message m)
                         ColorTranslator.ToWin32(Color.FromArgb(180, 180, 180)));
 
                     m.ResultInternal = (LRESULT)s_darkEditBrush;
+                    return;
                 }
-                else
+
+                // Additional handling for Simple style listbox when disabled
+                if (DropDownStyle == ComboBoxStyle.Simple && Application.IsDarkModeEnabled && !Enabled)
                 {
-                    m.ResultInternal = (LRESULT)(nint)InitializeDCForWmCtlColor((HDC)(nint)m.WParamInternal, m.MsgInternal);
+                    if (hwndChild == _childListBox?.HWND)
+                    {
+                        PInvokeCore.SetBkColor(
+                            (HDC)m.WParamInternal,
+                            ColorTranslator.ToWin32(Color.FromArgb(64, 64, 64)));
+
+                        PInvokeCore.SetTextColor(
+                            (HDC)m.WParamInternal,
+                            ColorTranslator.ToWin32(Color.FromArgb(180, 180, 180)));
+
+                        m.ResultInternal = (LRESULT)s_darkEditBrush;
+                        return;
+                    }
                 }
-#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.
+#pragma warning restore WFO5001
 
                 break;
+
+            case PInvokeCore.WM_CTLCOLOREDIT:
             case PInvokeCore.WM_CTLCOLORLISTBOX:
                 m.ResultInternal = (LRESULT)(nint)InitializeDCForWmCtlColor((HDC)(nint)m.WParamInternal, m.MsgInternal);
                 break;
@@ -3811,6 +3811,29 @@ protected override unsafe void WndProc(ref Message m)
                     using Graphics g = Graphics.FromHdcInternal((IntPtr)dc);
                     FlatComboBoxAdapter.DrawFlatCombo(this, g);
 
+#pragma warning disable WFO5001
+                    // Special handling for disabled DropDownList in dark mode
+                    if (Application.IsDarkModeEnabled && !Enabled && DropDownStyle == ComboBoxStyle.DropDownList)
+                    {
+                        // The text area for DropDownList (excluding the dropdown button)
+                        Rectangle textBounds = ClientRectangle;
+                        textBounds.Width -= SystemInformation.VerticalScrollBarWidth;
+
+                        // Fill the background
+                        using var bgBrush = new SolidBrush(Color.FromArgb(64, 64, 64));
+                        g.FillRectangle(bgBrush, textBounds);
+
+                        // Draw the text
+                        TextRenderer.DrawText(
+                            g,
+                            Text,
+                            Font,
+                            textBounds,
+                            Color.FromArgb(180, 180, 180),
+                            TextFormatFlags.Left | TextFormatFlags.VerticalCenter | TextFormatFlags.EndEllipsis);
+                    }
+#pragma warning restore WFO5001
+
                     return;
                 }
 

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

@@ -1320,14 +1320,9 @@ public override string Text
 
             if (!IsHandleCreated && _textRtf is null)
             {
-                if (_textPlain is not null)
-                {
-                    return _textPlain;
-                }
-                else
-                {
-                    return base.Text;
-                }
+                return _textPlain is not null
+                    ? _textPlain
+                    : base.Text;
             }
             else
             {
@@ -1457,14 +1452,10 @@ public unsafe float ZoomFactor
                 int numerator = 0;
                 int denominator = 0;
                 PInvokeCore.SendMessage(this, PInvokeCore.EM_GETZOOM, (WPARAM)(&numerator), ref denominator);
-                if ((numerator != 0) && (denominator != 0))
-                {
-                    _zoomMultiplier = numerator / ((float)denominator);
-                }
-                else
-                {
-                    _zoomMultiplier = 1.0f;
-                }
+
+                _zoomMultiplier = (numerator != 0) && (denominator != 0)
+                    ? numerator / ((float)denominator)
+                    : 1.0f;
 
                 return _zoomMultiplier;
             }
@@ -2412,24 +2403,6 @@ protected override void OnGotFocus(EventArgs e)
         }
     }
 
-    protected override void OnEnabledChanged(EventArgs e)
-    {
-        base.OnEnabledChanged(e);
-        HandleDarkModeDisabledBackground();
-    }
-
-    private void HandleDarkModeDisabledBackground()
-    {
-#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 (Application.IsDarkModeEnabled
-            && !Enabled
-            && DarkModeRequestState is true)
-        {
-            Invalidate();
-        }
-#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.
-    }
-
     protected override void OnHandleCreated(EventArgs e)
     {
         // base.OnHandleCreated is called somewhere in the middle of this
@@ -2476,8 +2449,6 @@ protected override void OnHandleCreated(EventArgs e)
         // base sets the Text property. It's important to do this *after* setting EM_AUTOUrlDETECT.
         base.OnHandleCreated(e);
 
-        HandleDarkModeDisabledBackground();
-
         // For some reason, we need to set the OleCallback before setting the RTF property.
         UpdateOleCallback();
 
@@ -2706,14 +2677,9 @@ private void SendZoomFactor(float zoom)
             PInvokeCore.SendMessage(this, PInvokeCore.EM_SETZOOM, (WPARAM)numerator, (LPARAM)denominator);
         }
 
-        if (numerator != 0)
-        {
-            _zoomMultiplier = numerator / ((float)denominator);
-        }
-        else
-        {
-            _zoomMultiplier = 1.0f;
-        }
+        _zoomMultiplier = numerator != 0
+            ? numerator / ((float)denominator)
+            : 1.0f;
     }
 
     private unsafe bool SetCharFormat(CFM_MASK mask, CFE_EFFECTS effect, RichTextBoxSelectionAttribute charFormat)
@@ -2907,14 +2873,9 @@ private void StreamIn(Stream data, uint flags)
             // set up structure to do stream operation
             EDITSTREAM es = default;
 
-            if ((flags & PInvoke.SF_UNICODE) != 0)
-            {
-                cookieVal = INPUT | UNICODE;
-            }
-            else
-            {
-                cookieVal = INPUT | ANSI;
-            }
+            cookieVal = (flags & PInvoke.SF_UNICODE) != 0
+                ? INPUT | UNICODE
+                : INPUT | ANSI;
 
             if ((flags & PInvoke.SF_RTF) != 0)
             {
@@ -3461,26 +3422,42 @@ private void WmSetFont(ref Message m)
         InternalSetForeColor(ForeColor);
     }
 
-    protected override void WndProc(ref Message m)
+    protected override unsafe void WndProc(ref Message m)
     {
         switch (m.MsgInternal)
         {
 #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.
             case PInvokeCore.WM_PAINT:
-                if (IsHandleCreated && !Enabled)
+                if (Handle == m.HWND
+                    && !Enabled
+                    && Application.IsDarkModeEnabled)
                 {
-                    if (Application.IsDarkModeEnabled && DarkModeRequestState is true)
-                    {
-                        // If the control is in dark mode, we need to paint the background
-                        // with the dark mode color.
-                        using Graphics g = Graphics.FromHwnd(Handle);
-                        g.Clear(SystemColors.Control);
-                    }
+                    base.WndProc(ref m);
+
+                    // If the control is disabled, we don't want to let the RTF control
+                    // paint anything else. We will paint the background and the text
+                    // ourselves, so we don't want the RTF control to paint the background
+                    // and the text in the foreground color.
+                    using Graphics g = Graphics.FromHwndInternal(Handle);
+
+                    // Paint the background
+                    g.FillRectangle(SystemBrushes.ControlDark, ClientRectangle);
+
+                    // Paint the text
+                    TextRenderer.DrawText(
+                        g,
+                        Text,
+                        Font,
+                        ClientRectangle,
+                        SystemColors.GrayText,
+                        TextFormatFlags.Left | TextFormatFlags.VerticalCenter);
+
+                    return;
                 }
 
                 base.WndProc(ref m);
-                break;
 
+                break;
 #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.
 
             case MessageId.WM_REFLECT_NOTIFY: