Question

I wish to create a countdown timer in my app in such a way that I can give a certain duration (like 15 minutes or 15:00) and it starts on an action.

I also need for that countdown timer to take elapsed time duration and total time duration information from an external web service and start the countdown for the remaining time.

This is actually for a quiz application where the user will be presented with a series of questions and the timer will be placed on the question screen (for the whole quiz and not for only one question). The user can set the duration for the quiz and the countdown timer will begin as soon as the user start taking the quiz. There is also a pause functionality where user can pause the test and the information of time elapsed and total time duration will be registered in a web-service. The user can resume the quiz anytime with the countdown timer starting right from the time it was paused (taking this information from the web-service, that is).

Thanks in advance.

PS: To be honest, I had no idea on how to go about it. There was too much of confusion on what format will the time be stored over in the web-service and a lot of other stuff like if the program will go forward after the NSTimer is running in a loop etc. So you know what I mean. Yes, NSTimer does solve the problem as Alex told and provided with a sample code as well.

Answer 1

Look at the docs for NSTimer.

Generally, you would create an NSTimer which calls a method every second, like so:

NSTimer *theTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(tick) userInfo:nil repeats:YES];

Then in tick, you would decrement a variable holding the time remaining, and update a label on the display.

Also, if you want some working sample code, check out my little countdown app on GitHub.