> From: "Albert" <georgealbert@qq.com>
> Cc: "emacs-devel" <emacs-devel@gnu.org>
> Date: Mon, 13 Apr 2020 15:07:19 +0800
> 
> Thanks. I'll try it.

I'm also worried by your use of w32_system_caret_hwnd as the handle of
the window for which to retrieve the input context.
w32_system_caret_hwnd is not guaranteed to be a valid handle if the
system caret is not used, i.e. if w32-use-visible-system-caret is nil
(which is the default).

So perhaps instead of using w32_system_caret_hwnd, you should use the
return value of GetFocus function, similar to what we do elsewhere in
w32_msg_pump.