c# - Detect when none of app windows is active/focused -

how detect when user changes focus multi-window application (alt+tab e.g.).

i want detect when none of app windows active/focused.

first window shown user can work 4 windows(none of these shown dialog).

form has containsfocus property indicates whether form, or 1 of child controls has input focus. can check property open forms detect if application contains focus or not:

var isactive = application.openforms.cast<form>().any(x=>x.containsfocus); 

if want notified of state of application in small periods of time, can use in tick event of timer.