NSMutableDictionary with NSTimers - objective-c

Question

There are several recipes in my CoreData. Every recipe has attributes prepHour and prepMin. I would like by tapping to button Start Timer start countdown timer. But there can be several timers (for example for each recipe) which must work simultaneously
I selected this way (may be it's wrong):
For timers I used singleton Timers.
By tapping to my Start Timer I call method with parameters (name, prepHour, prepMin)
My startTimer method creates timer and puts it to NSMutableDictionary
Calling method:
[[Timers sharedTimers] startTimer:self.recipe.name startTimer:self.recipe.prepHour startTimer:self.recipe.prepMin];
In Timers singleton:
- (void)startTimer:(NSString *)timerName startTimer:(NSNumber *)hVal startTimer:(NSNumber *)mVal
{
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:60.0f target:self selector:#selector(tick:) userInfo:nil repeats:YES];
if ([timer isValid]) {
NSArray *array = [NSArray arrayWithObjects: timer, hVal, mVal, nil];
if (_timerDict == NULL) {
_timerDict = [[NSMutableDictionary alloc] init];
}
[_timerDict setObject:array forKey:timerName];
NSLog(#"%#", _timerDict);
}
}
- (void)stopTimer:(NSString *)timerName
{
NSArray *array = [_timerDict objectForKey:timerName];
NSTimer *timer = [array objectAtIndex:0];
if ([timer isValid]) {
[timer invalidate];
[_timerDict removeObjectForKey:timerName];
}
}
- (void)tick:(NSString *)timerName
{
NSArray *array = [_timerDict objectForKey:timerName];
//NSTimer *timer = [array objectAtIndex:0];
NSInteger hVal = [[array objectAtIndex:1] integerValue];
NSInteger mVal = [[array objectAtIndex:2] integerValue];
NSInteger sVal = 0;
How should I use tick method for each timer? I would like each timer call this method with own parameters (timer, prepHour, prepMin)

Answer 1

This may be a matter of taste, but I don't use timers to remember an expiration time, I use them to pulse at a frequency. For your app, I'd use one timer at the lowest common denominator frequency, like one second. Instead of a singleton, I have a single timer, that the app delegate can invalidate and restart.
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(tick:) userInfo:nil repeats:YES];
Then keep each expiration as one property on each recipe. For example:
- (IBAction)pressedStartButtonForRecipeA:(id)sender {
// this is a NSDate * property
self.recipeADone = [NSDate dateWithTimeIntervalSinceNow:90*60]; // ninety minutes
}
- (void)tick:(NSTimer *)timer {
NSDate *now = [NSDate date];
NSTimeInterval secondsUntilAIsDone = [self.recipeADone timeIntervalSinceDate:now];
if (secondsUntilAIsDone <= 0.0) {
// update UI to say that A is done
} else {
// update UI to reduce countdown
}
// and so on for all recipes
}

Answer 2

This sounds like a poor use of a singleton. I would have…well, one timer per timer if you want to go with this design. Alternatively, you could have one timer and just calculate the offset from each timer's start when it ticks. (Which approach makes sense depends on your particular app. I'd usually go with the second, but YMMV.)
Also, timers do not pass an NSString to their callback; they pass themselves. To allow the callback to get some information from the timer, you can set the info its the timer's userInfo dictionary.