How i can know which android apps are currently connected through internet.?

[BibekKumar]

I have used many apps like onavo,my data manager etc.they don't have ability to show live data usage by apps. some apps are using internet in background like gmail and widget of yahoo news, drippler and many others even i don't open it.thats why i want to know which android apps are currently connected through internet and how much data they are eating.