Use focused thread for GetKeyboardLayout

src/ManagedShell.Common/Helpers/KeyboardLayoutHelper.cs

@@ -1,18 +1,51 @@
 using ManagedShell.Common.Structs;
 using ManagedShell.Interop;
+using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Runtime.InteropServices;
+using static ManagedShell.Interop.NativeMethods;
 
 namespace ManagedShell.Common.Helpers
 {
     public static class KeyboardLayoutHelper
     {
+        private static uint GetFocusedThreadId()
+        {
+            var gti = new GUITHREADINFO();
+            gti.cbSize = Marshal.SizeOf(typeof(GUITHREADINFO));
+
+            // Some apps (e.g. Electron/WebView2 apps such as Teams, and WinUI3 apps such as the
+            // modern Notepad) keep their real keyboard focus on a child window that belongs to a
+            // different thread than the top-level foreground window. GetGUIThreadInfo(0, ...)
+            // resolves the true focused window first.
+            // idThread 0 asks for the foreground thread's queue; hwndFocus within it is the
+            // window that truly owns keyboard focus, which may belong to a different thread
+            // than the top-level foreground window itself.
+            if (GetGUIThreadInfo(0, ref gti))
+            {
+                IntPtr focusedWindow = gti.hwndFocus != IntPtr.Zero ? gti.hwndFocus : gti.hwndActive;
+
+                if (focusedWindow != IntPtr.Zero)
+                {
+                    uint focusedThreadId = GetWindowThreadProcessId(focusedWindow, out _);
+
+                    if (focusedThreadId != 0)
+                    {
+                        return focusedThreadId;
+                    }
+                }
+            }
+
+            return GetWindowThreadProcessId(GetForegroundWindow(), out _);
+        }
+
         public static KeyboardLayout GetKeyboardLayout(bool currentThread = false)
         {
             uint threadId = 0;
             if (!currentThread)
-                threadId = NativeMethods.GetWindowThreadProcessId(NativeMethods.GetForegroundWindow(), out _);
+                threadId = GetFocusedThreadId();
             var layout = NativeMethods.GetKeyboardLayout(threadId);
 
             return new KeyboardLayout()
@@ -39,10 +72,10 @@ public static List<KeyboardLayout> GetKeyboardLayoutList()
 
         public static bool SetKeyboardLayout(int layoutId)
         {
-            return NativeMethods.PostMessage(0xffff,
-                (uint) NativeMethods.WM.INPUTLANGCHANGEREQUEST,
+            return PostMessage(0xffff,
+                (uint) WM.INPUTLANGCHANGEREQUEST,
                 0,
-                (long)NativeMethods.LoadKeyboardLayout(layoutId.ToString("x8"), (uint)(NativeMethods.KLF.SUBSTITUTE_OK | NativeMethods.KLF.ACTIVATE)));
+                (long)LoadKeyboardLayout(layoutId.ToString("x8"), (uint)(KLF.SUBSTITUTE_OK | KLF.ACTIVATE)));
         }
     }
 }

src/ManagedShell.Interop/NativeMethods.User32.cs

@@ -3857,5 +3857,22 @@ public struct DEV_BROADCAST_HANDLE
 
         [DllImport(User32_DllName)]
         public static extern bool UnregisterDeviceNotification(IntPtr handle);
+
+        [StructLayout(LayoutKind.Sequential)]
+        public struct GUITHREADINFO
+        {
+            public int cbSize;
+            public uint flags;
+            public IntPtr hwndActive;
+            public IntPtr hwndFocus;
+            public IntPtr hwndCapture;
+            public IntPtr hwndMenuOwner;
+            public IntPtr hwndMoveSize;
+            public IntPtr hwndCaret;
+            public Rect rcCaret;
+        }
+
+        [DllImport(User32_DllName, SetLastError = true)]
+        public static extern bool GetGUIThreadInfo(uint idThread, ref GUITHREADINFO lpgui);
     }
 }