Merge pull request #6597 from AvaloniaUI/fixes/6592-win32-alt-f10

Win32: Fix handling of subsequent keypress after Alt/F10

src/Windows/Avalonia.Win32/Interop/UnmanagedMethods.cs

@@ -808,6 +808,31 @@ namespace Avalonia.Win32.Interop
             MNC_SELECT = 3
         }
 
+        public enum SysCommands
+        {
+            SC_SIZE = 0xF000,
+            SC_MOVE = 0xF010,
+            SC_MINIMIZE = 0xF020,
+            SC_MAXIMIZE = 0xF030,
+            SC_NEXTWINDOW = 0xF040,
+            SC_PREVWINDOW = 0xF050,
+            SC_CLOSE = 0xF060,
+            SC_VSCROLL = 0xF070,
+            SC_HSCROLL = 0xF080,
+            SC_MOUSEMENU = 0xF090,
+            SC_KEYMENU = 0xF100,
+            SC_ARRANGE = 0xF110,
+            SC_RESTORE = 0xF120,
+            SC_TASKLIST = 0xF130,
+            SC_SCREENSAVE = 0xF140,
+            SC_HOTKEY = 0xF150,
+            SC_DEFAULT = 0xF160,
+            SC_MONITORPOWER = 0xF170,
+            SC_CONTEXTHELP = 0xF180,
+            SC_SEPARATOR = 0xF00F,
+            SCF_ISSECURE = 0x00000001,
+        }
+
         [StructLayout(LayoutKind.Sequential)]
         public struct RGBQUAD
         {

src/Windows/Avalonia.Win32/WindowImpl.AppWndProc.cs

@@ -123,6 +123,12 @@ namespace Avalonia.Win32
                         break;
                     }
 
+                case WindowsMessage.WM_SYSCOMMAND:
+                    // Disable system handling of Alt/F10 menu keys.
+                    if ((SysCommands)wParam == SysCommands.SC_KEYMENU && HighWord(ToInt32(lParam)) <= 0)
+                        return IntPtr.Zero;
+                    break;
+
                 case WindowsMessage.WM_MENUCHAR:
                     {
                         // mute the system beep