Hi,
Currently, JUCE apps can be notified about suspended states with JUCEApplicationBase::suspended(), which is called once the app is already suspended. Some operating systems, like iOS, allow apps to be notified a moment before they become inactive; see the UIKit documentation here.
Would it be possible to interface iOS’s applicationWillResignActive in JUCE? Perhaps by adding a virtual method called JUCEApplicationBase::aboutToSuspend()?
I can see JUCE already uses applicationWillResignActive in juce_Windowing_ios.mm for managing internal callbacks so I think implementation wouldn’t be very trivial.