ios - Store a value for "total number of time spent" in iPhone app -

ios - Store a value for "total number of time spent" in iPhone app -

i developing iphone application stores total time spent @ activity. allow user press button start activity , stop. how can store value keeps adding time spent on activity overall in form of hours, minutes , seconds? (in core info or otherwise). example: can shown

total time spent in week: 08:12:05 mean user spent 8 hours, 12 minutes , 5 seconds on particular activity.

nsdate unable it. looked @ nstimer kind of opposite of i'm looking for. i'm not thorough api ios there can work with?

i store nsdates start , stop time, every time user starts activity. time spent can derived these dates -timeintervalsincedate:.

ios sqlite core-data nsdate