How Do I write a Timer in Objective-C? - iphone

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