如何在 ObjectiveC 中编写计时器

不要那样用NSTimer.NSTimer通常用于在某个时间间隔触发 Select 器.它的精度不高，不适合你想做的事情.

你想要的是High resolution timer级(使用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:增加了-timeElapsedInMilliseconds和-timeElapsedInMinutes的方法

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