From e9b745d1257cfcc1112f3d6ace6266cf02ea1d67 Mon Sep 17 00:00:00 2001
From: John Popovici <john@reincubate.com>
Date: Tue, 17 Jun 2025 17:00:55 +0300
Subject: [PATCH] Added event to forward HwndProc to avoid adding additional
 hooks and timing issues.

---
 .../Controls/TitleBar/HwndProcEventArgs.cs    | 33 +++++++++++++++++++
 src/Wpf.Ui/Controls/TitleBar/TitleBar.cs      | 11 +++++++
 2 files changed, 44 insertions(+)
 create mode 100644 src/Wpf.Ui/Controls/TitleBar/HwndProcEventArgs.cs

diff --git a/src/Wpf.Ui/Controls/TitleBar/HwndProcEventArgs.cs b/src/Wpf.Ui/Controls/TitleBar/HwndProcEventArgs.cs
new file mode 100644
index 000000000..dab7a6d14
--- /dev/null
+++ b/src/Wpf.Ui/Controls/TitleBar/HwndProcEventArgs.cs
@@ -0,0 +1,33 @@
+// This Source Code Form is subject to the terms of the MIT License.
+// If a copy of the MIT was not distributed with this file, You can obtain one at https://opensource.org/licenses/MIT.
+// Copyright (C) Leszek Pomianowski and WPF UI Contributors.
+// All Rights Reserved.
+
+// ReSharper disable once CheckNamespace
+namespace Wpf.Ui.Controls;
+
+public class HwndProcEventArgs : EventArgs
+{
+    public bool Handled { get; set; }
+
+    public IntPtr? ReturnValue { get; set; }
+
+    public bool IsMouseOverDetectedHeaderContent { get; }
+
+    public IntPtr HWND { get; }
+
+    public int Message { get; }
+
+    public IntPtr WParam { get; }
+
+    public IntPtr LParam { get; }
+
+    internal HwndProcEventArgs(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, bool isMouseOverDetectedHeaderContent)
+    {
+        HWND = hwnd;
+        Message = msg;
+        WParam = wParam;
+        LParam = lParam;
+        IsMouseOverDetectedHeaderContent = isMouseOverDetectedHeaderContent;
+    }
+}
diff --git a/src/Wpf.Ui/Controls/TitleBar/TitleBar.cs b/src/Wpf.Ui/Controls/TitleBar/TitleBar.cs
index 471ba3bfc..98dfd845e 100644
--- a/src/Wpf.Ui/Controls/TitleBar/TitleBar.cs
+++ b/src/Wpf.Ui/Controls/TitleBar/TitleBar.cs
@@ -37,6 +37,8 @@ public class TitleBar : System.Windows.Controls.Control, IThemeControl
 
     private DependencyObject? _parentWindow;
 
+    public event EventHandler<HwndProcEventArgs>? WndProcInvoked;
+
     /// <summary>Identifies the <see cref="ApplicationTheme"/> dependency property.</summary>
     public static readonly DependencyProperty ApplicationThemeProperty = DependencyProperty.Register(
         nameof(ApplicationTheme),
@@ -682,6 +684,15 @@ or User32.WM.NCLBUTTONUP
             }
         }
 
+        var e = new HwndProcEventArgs(hwnd, msg, wParam, lParam, isMouseOverHeaderContent);
+        WndProcInvoked?.Invoke(this, e);
+
+        if (e.ReturnValue != null)
+        {
+            handled = e.Handled;
+            return e.ReturnValue ?? IntPtr.Zero;
+        }
+
         switch (message)
         {
             case User32.WM.NCHITTEST when CloseWindowByDoubleClickOnIcon && _icon.IsMouseOverElement(lParam):