What recipient should be specified for the WM_INPUTLANGCHANGEREQUEST message?

Question

C++ / C#

In my layout switcher, I encountered the problem of switching layouts in Skype (judging by the reviews, this is not the only program in which this behavior is observed). The problem is rather strange: if there is only one letter in the message box, everything works as it should, otherwise the WM_INPUTLANGCHANGEREQUEST message is not processed. Message sending code:

public static void SetNextKeyboardLayout()
    {
        IntPtr hWnd = GetForegroundWindow();
        uint processId;
        uint activeThreadId = GetWindowThreadProcessId(hWnd, out processId);
        uint currentThreadId = GetCurrentThreadId();

        AttachThreadInput(activeThreadId, currentThreadId, true);
        IntPtr focusedHandle = GetFocus();
        AttachThreadInput(activeThreadId, currentThreadId, false);

        PostMessage(focusedHandle == IntPtr.Zero ? hWnd : focusedHandle, WM_INPUTLANGCHANGEREQUEST, INPUTLANGCHANGE_FORWARD, HKL_NEXT);
    }

focusedHandle was made for WPF applications, without this piece the layout does not switch in them. I suspect that I am incorrectly specifying the recipient of the message. It's just that GetForegroundWindow() doesn't work, nor does any combination of GetParentWindow(). Where should this message be sent?

Answer 1

In my switch, I use this piece of code (collected from the world by thread)

void function()
{
  var threadInfo = new WinAPI.GUITHREADINFO();
  threadInfo.cbSize = Marshal.SizeOf(threadInfo);
  WinAPI.GetGUIThreadInfo(0, ref threadInfo);

  IntPtr hWnd = (threadInfo.hwndFocus != IntPtr.Zero) ? threadInfo.hwndFocus : threadInfo.hwndActive;
  WinAPI.PostMessage(hWnd, WinAPI.WM_INPUTLANGCHANGEREQUEST, WinAPI.WM_INPUTLANGCHANGE_SYSCHARSET, (int)_seconLayot);
}

where WinAPI is just a class with described structures and Dll imports. I don't have any issues with switching.