问题
I am not planning to send this app to AppStore. It's just an experimental app. So, I am not worried about AppStore approval/rejection.
I am looking for a way, how I can determine
a) What is the current foreground app (my app will be in the background at that moment. I may use audio player or voip for this)
b) Detect when new application became foreground app
回答1:
It looks like this question has this answer for mine question. how to determine which apps are background and which app is foreground on iOS by application id
It boils down to SBFrontmostApplicationDisplayIdentifier private API
来源：https://stackoverflow.com/questions/11299957/is-there-a-private-api-to-be-able-to-detect-what-is-current-foreground-app-on-io