Question

I need to create a Timer that counts down from a string I get from the server. the string outputs total seconds left.

I am using this code – it calculates the initial number time right and it counts down but the minutes are the problem.

EDIT – Every real minute the minute calculation goes up by one. But I don’t understand why it is doing this.

-(void)showTimmer:(id) sender {

//get total amount of seconds

NSString *timeRaw =  [ArrayFromServer objectAtIndex:1];
NSArray *timeArr = [timeRaw componentsSeparatedByString:@","];
timetoInt =  [timeArr objectAtIndex:0];
int time1 = [timetoInt intValue];

//set the second countdown

NSDate* now = [NSDate date];    
NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *dateComponents = [gregorian components:(NSSecondCalendarUnit) fromDate:now];

NSInteger seconds = time1 - [dateComponents second];

[gregorian release];

// do the hours days maths

int hour = (seconds / 3600 );
seconds -= hour * 3600;
int minute = (seconds / 60 );
seconds -= minute * 60;
int second = seconds;

//set the labels

countdownLabel.text = [NSString stringWithFormat:@"%02dH %02dM %02ds", hour, minute, second];

Answer 1

You’re using your pliers to drive a screw. The seconds method of an NSDateComponents gives you what you would see on a clock if you looked at the second hand at the time represented by your NSDate. For example, as I type this, it’s UTC Saturday March 26, 2011, 02:52:04. If I got [NSDate date], turned it into an NSDateComponents and asked that for its seconds, I’d get “4”. If I did it again in a second, I’d get “5”, and when the minute clicked over, I’d get “59”, then “0”.

You can verify this for yourself; put this in your timer method:

NSInteger dcSecond = [dateComponents second];
NSLog(@"%d", dcSecond);

So every time the minute of the actual clock ticks over, your calculation of the remaining time:

NSInteger seconds = time1 - [dateComponents second];

subtracts 0 from time1 and gives you back time1. That’s why you’re having the problem.

The way* to fix it is to dump the calendar stuff and use CFAbsoluteTimeGetCurrent(). First, put the start time in your timer’s userInfo (or in an ivar if you prefer):

[NSTimer scheduledTimer...
        // The function returns CFAbsoluteTime, which is a
        // typedef'd double but you're already working with
        // integers, so use a cast
             userInfo:[NSNumber numberWithInteger:(NSInteger)CFAbsoluteTimeGetCurrent()]
                ...];

Then change your calculation of the remaining time (the variable you call seconds:

NSInteger startTime = [[timer userInfo] integerValue];
NSInteger currTime = (NSInteger)CFAbsoluteTimeGetCurrent();
NSInteger elapsedTime = currTime - startTime;
NSInteger duration = time1 - startTime;
//NSInteger seconds = time1 - [dateComponents second];
NSInteger remaining =  duration - elapsedTime;

int hour = remaining / 3600;
...

---

*: Well, one way, but I think probably the best.