Question

I am writing an onscreen keyboard and would like to redraw my layout as soon as keyboard layout is changed.

Currently I call:

GetKeyboardLayout(GetWindowThreadProcessId(GetForegroundWindow(), NULL));

on every key press to find out if the layout has changed. It does not work if user changes the layout by mouse, until key is pressed.

I would like to know if there is any way to get notified
when the keyboard layout of the current foreground window is changed,
so I can redraw my layout as soon as the change happens.

Answer 1

There is a way …

First you need to register your application to capture foreground window changes:
Use SetWinEventHook with EVENT_SYSTEM_FOREGROUND (and WINEVENT_OUTOFCONTEXT as it’s .NET) for that.

If that happens: Use your GetKeyboardLayout solution for getting the current layout of that window.

Then use a local Windows Hook (you’re probably using it low-level-globally for key captures) with WH_CALLWNDPROC and the thread of the new foreground window.
Listen to WM_INPUTLANGCHANGE messages to that window to receive changes to the layout.
(You may want to unhook/rehook after another foreground change)