Objective-C, Displaying an NSTimer activated by a UIButton - objective-c

Question

I'm working on a project for school that includes a set of buttons that create NStimers used as a countdown timer. Ideally, the time would display as the title of the UIButton that started the timer.
So far I have only been able make this work if when setting the display of the time I refer to a specific instance of a UIButton rather than a somehow passing a UIButton argument.
I also have declared "time" NSString that holds the current displayed value calculated by the NSTimer. This is not how the final implementation should be, and I only have it set up like this just to have it partially working.
Code for one of the buttons:
b1 = [[UIButton alloc]
initWithFrame:CGRectMake(neutral.frame.size.width * 0.56, neutral.frame.size.height * 0.18, neutral.frame.size.height * 0.64, neutral.frame.size.height * 0.64)];
[b1.titleLabel setFont:[UIFont fontWithName:#"Helvetica-Bold" size:35.0]];
[b1 setBackgroundImage: forState:UIControlStateNormal];
Method called from button press action:
-(void)buttonClicked:(id)sender
{
//do stuff
timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(timerFired) userInfo:[NSNumber numberWithInt:t] repeats:YES]; }
NSTimer timer fired method:
-(void)timerFired
{
if((curMin>0 || curSec>=0) && curMin>=0)
{
if(curSec==0)
{
curMin-=1;
curSec=59;
}
else if(curSec>0)
{
curSec-=1;
}
if(curMin>-1)
{
time = [NSString stringWithFormat: #"%d%#%02d",curMin,#":",curSec];
[b1 setTitle:time forState:UIControlStateNormal];
}
}
else
{
[b1 setTitle: nil forState:UIControlStateNormal];
[timer invalidate];
}
}
I hope that was clear enough as to what I am trying to accomplish. I am somewhat surprised that I haven't been able to find anything to walk me through this. I am flexible to changing how exactly this works. All that really matters is that each button can start a unique countdown timer.
I'm sure that this code is sloppy, but Objective C is relatively new to me so any help at all would be appreciated.

Answer 1

Don't store time as minutes/seconds, just use seconds, as all that greater than 60 logic is really tedious isn't it.
I've chosen to call the instance variable _secondsLeft so I will know what it means when I look at the code in 6 months time:
-(void)timerFired
{
NSString *formatted = #"";
if (secondsLeft > 0)
{
secondsLeft--;
formatted = [NSString stringWithFormat:#"%d:%02d", (secondsLeft / 60), (secondsLeft % 60)];
} else {
[timer invalidate];
}
[b1 setTitle:formatted forState:UIControlStateNormal];
}