How to Create a count up timer in iOS - ios

Question

I have this code:
NSDate *now = [NSDate date];
static NSDateFormatter *dateFormatter;
if (!dateFormatter) {
dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = #"h:mm:ss";
}
recordStatusLabel.text = [dateFormatter stringFromDate:now];
NSLog(#"Time now: %#", [dateFormatter stringFromDate:now]);
that counts the current time. How can i change it to start in this format?
00:00:00 (hours:minutes:seconds)
from a NSString variable:
Example: i got this value for my variable
NSString * time = #"02:16:23";
then the counter will continue the count to:
02:16:24
.
.
.
02:20:13

Answer 1

Create an instance of NSTimer class and set time for event fire 1 second with repeat option YES. In the event handling update your label with current time. When your functionality is complete, invalidate the timer to stop firing events.
Here is the code to create instance of NSTimer class:
NSTimer *countUpTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self
selector:#selector(countUpTimerFired:) userInfo:nil repeats:YES];
Here is the method for event handling:
- (void)countUpTimerFired:(id)sender {
dispatch_async(dispatch_get_main_queue(), ^{
recordStatusLabel.text = [dateFormatter stringFromDate:[NSDate date]];
});
}
Keep of dateFormatter and countUpTimer as class variables.
This is the simple approach to achieve your required functionality as you are starting your time from current device time; So you won't be requiring extra efforts to get value from label, incrementing the value and then converting back to string.
EDIT:
If you want to start the counter from anyother time value or from a string, you can keep a integer variable to keep the value of time in seconds. Then increment the value when timer event gets called (every second) and then converting that integer to time string.
Here's the code for initial value:
NSString *timeString = recordStatusLabel.text; //contains a string in time format like #"2:16:23" or #"00:00:00" or current time or any other value.
NSArray *timeComponents = [timeString componentsSeparatedByString:#":"];
int timeInSeconds = [timeComponents[0] intValue]*3600 + [timeComponents[1] intValue]*60 + [timeComponents[2] intValue];
in the event handling of timer:
- (void)countUpTimerFired:(id)sender {
timeInSeconds++;
int hours = timeInSeconds/3600;
int minutes = (timeInSeconds%3600)/60;
int seconds = timeInSeconds%60;
dispatch_async(dispatch_get_main_queue(), ^{
[recordStatusLabel setText:[NSString stringWithFormat:#"%d:%02d:%02d", hours, minutes, seconds]];
});
}

Answer 2

Since you are dealing with a timer which the fastest value is the second, then to achieve performance you just fire a timer which repeats every second.
Declare your instance variables
#implementation Yourclass {
NSDate *startDate;
NSTimer *yourTimer;
NSString *myTime;
}
When you click a button to start timer
-(IBAction)startTimer:(id)sender {
startDate = [NSDate date];
yourTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(timeHandler:) userInfo:nil repeats:YES];
[yourTimer fire];
}
Implement your method which is the handler method of timer
-(void)timeHandler:(NSTimer *)myTimer {
//Difference between dates in seconds
NSTimeInterval elapsedTime = [startDate timeIntervalSinceNow];
//Divide by 3600 to get the hours
NSInteger hours = elapsedTime/3600;
//Divide by 60 to get the minutes
NSInteger minutes = elapsedTime/60;
NSInteger seconds = elapsedTime;
myTime = [NSString stringWithFormat:#"%i:%i:%i",hours, minutes, seconds];
// update the label
recordStatusLabel.text = myTime;
}