How to start a timer from zero in iOS - ios

Question

I have a button on which i have placed a UITapGestureRecognizer. When i tap on that button, i call a method that starts the time.
My question is, i am able to get the timer string on a label. But the timer starts from current date-time, and i want to start the timer always from zero(like a countdown timer). Here below is my code for timer.
-(IBAction)micPressed{
if (gestureRecognizer.state==UIGestureRecognizerStateBegan) {
gestureRecognizer.view.alpha=0.2f;
[label setHidden:NO];
if (!_timer) {
_timer = [NSTimer scheduledTimerWithTimeInterval:0.1f
target:self
selector:#selector(_timerFired:)
userInfo:nil
repeats:YES];
}
}
else{
[label setHidden:YES];
gestureRecognizer.view.alpha=10.2f;
if ([_timer isValid]) {
[_timer invalidate];
}
_timer = nil;
}
}
- (void)_timerFired:(NSTimer *)timer {
NSDateFormatter *dateformatter=[[NSDateFormatter alloc]init];
[dateformatter setDateFormat:#"mm:ss:SSS"];
NSString *dateInStringFormated=[dateformatter stringFromDate:[NSDate dateWithTimeIntervalSinceNow:0]];
NSLog(#"%#",dateInStringFormated);
[label setText:dateInStringFormated];
}
Please can anyone suggest me the solution. Any help is appreciated.

Answer 1

Your code should be like,
NSDateFormatter *dateformatter=[[NSDateFormatter alloc]init];
[dateformatter setDateFormat:#"mm:ss:SSS"];
NSString *dateInStringFormated=[dateformatter stringFromDate:[dateformatter dateFromString:#"00:00:000"]];
NSLog(#"test : %#",dateInStringFormated);
I have just chage [NSDate dateWithTimeIntervalSinceNow:0] with [dateformatter dateFromString:#"00:00:000"].
It will start with zero always.
Update :
I think you want something like timer that update minutes,seconds and milliseconds as i understand your question now. You can achieve it something like,
Schedule timer like,
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:#selector(updateTimer) userInfo:nil repeats:YES];
Now your updateTimer should be like,
-(void)updateTimer{
static double counter = 0;
static int counter2 = 0;
int seconds = (int)counter % 60;
int minutes = ((int)counter / 60) % 60;
NSLog(#"%02d:%02d:%03d",minutes,seconds,counter2); // This should be your labels text that updating continuously
counter = counter + 0.01;
counter2++;
if (counter2 == 100) {
counter2 = 0;
}
}
Hope this will help :)

Answer 2

The problem is you are starting your timer from current time itself. To make a like countdown timer. You need to do the following:
Take an int named Counter and intialize it from 0
Fire your NSTimer and at that time increase the counter
Display the counter value in the UILabel text.
Once your NSTimer stops, again make it to 0.
That's it! This is how you can achieve the desired result.
Code:
int counter = 0;
- (void)_timerFired:(NSTimer *)timer {
counter++;
}
Once NSTimer is invalidate again make it to counter = 0

Answer 3

Remember the time when you have started the timer:
_startDate = [NSDate date];
_Timer = ...
Then use the time interval since the start date in your _timerFired method:
NSDateComponentsFormatter *formatter = [[NSDateComponentsFormatter alloc] init];
NSString *dateInStringFormatted = [formatter stringFromTimeInterval:[[NSDate date] timeIntervalSinceDate:_startDate]];