如何在iOS中从零开始计时

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

The problem is you are starting your timer from current time itself. To make a like countdown timer. You need to do the following:

1. Take an int named Counter and intialize it from 0
2. Fire your NSTimer and at that time increase the counter
3. Display the counter value in the UILabel text.
4. 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 2

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 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]];