Question

I am trying to make a stop watch with NSTimer.

I gave the following code:

 nst_Timer = [NSTimer scheduledTimerWithTimeInterval:0.001 target:self selector:@selector(showTime) userInfo:nil repeats:NO];

and it is not working in milliseconds. It takes more than 1 millisecond.

Answer 1

Don’t use NSTimer that way. NSTimer is normally used to fire a selector at some time interval. It isn’t high precision and isn’t suited to what you want to do.

What you want is a High resolution timer class (using NSDate):

Output:

Total time was: 0.002027 milliseconds
Total time was: 0.000002 seconds
Total time was: 0.000000 minutes

Main:

Timer *timer = [[Timer alloc] init];

[timer startTimer];
// Do some work
[timer stopTimer];

NSLog(@"Total time was: %lf milliseconds", [timer timeElapsedInMilliseconds]);  
NSLog(@"Total time was: %lf seconds", [timer timeElapsedInSeconds]);
NSLog(@"Total time was: %lf minutes", [timer timeElapsedInMinutes]);

Edit: Added methods for -timeElapsedInMilliseconds and -timeElapsedInMinutes

Timer.h:

#import <Foundation/Foundation.h>

@interface Timer : NSObject {
    NSDate *start;
    NSDate *end;
}

- (void) startTimer;
- (void) stopTimer;
- (double) timeElapsedInSeconds;
- (double) timeElapsedInMilliseconds;
- (double) timeElapsedInMinutes;

@end

Timer.m

#import "Timer.h"

@implementation Timer

- (id) init {
    self = [super init];
    if (self != nil) {
        start = nil;
        end = nil;
    }
    return self;
}

- (void) startTimer {
    start = [NSDate date];
}

- (void) stopTimer {
    end = [NSDate date];
}

- (double) timeElapsedInSeconds {
    return [end timeIntervalSinceDate:start];
}

- (double) timeElapsedInMilliseconds {
    return [self timeElapsedInSeconds] * 1000.0f;
}

- (double) timeElapsedInMinutes {
    return [self timeElapsedInSeconds] / 60.0f;
}

@end