How can i switch window between two GTK+ APP. ?

["godsatan" <godsatan kimo com tw>]

Dear Sirs,

I have 2 GTK+ app. One is main app and another is EMAIL-checker, both have
gtk_main() and designed for different tasks. Recently, i need to combine
these two app. Initially, main app runs first and i want to trigger the
email-checker running later by press some remote controller keys. Here is my
problem. In my system, i don't have mouse and keyboard to choose whick app's
window i want to see. So, how can i swtich window from main to email-cheker
or form email-checker to main? In other words, how can i get the widget or
window id form another app? Please feel free to give me some advise, i need
your help. Thanks a lot!!

Best Regards,
Calvin Chen