iphone - How to call Web service Continuously in ios -

i have ios app.

in have multi user account.so multiple user can login.

when 1 user see other user profile , if user online want notify him.

i can't how implement it.

if have continuously check flag value on server if has checked profile or how can handle it?

remote notifications way it. logic on when , has notified can handled @ server.

you may have seen lots of apps asking permissions send notification. downside being if user denies permission.

polling client side can 1 of methods can used , require client of computation.

so in all, call got take considering building.