##Creating a timer with Grand Central Dispatch

At the following is the implementation file of a sample class that shows, how to make a timer with the help of Grand Central Dispatch. The timer fires on a global queue, just change the queue to the main queue or any custom queue and the timer fires on this queue and not on the global queue anymore.

```objc

#import <Foundation/Foundation.h>

@interface SampleClass : NSObject
- (void)startTimer;
- (void)cancelTimer;
@end


#import "SampleClass.h"

dispatch_source_t CreateDispatchTimer(double interval, dispatch_queue_t queue, dispatch_block_t block)
{
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    if (timer)
    {
        dispatch_source_set_timer(timer, dispatch_time(DISPATCH_TIME_NOW, interval * NSEC_PER_SEC), interval * NSEC_PER_SEC, (1ull * NSEC_PER_SEC) / 10);
        dispatch_source_set_event_handler(timer, block);
        dispatch_resume(timer);
    }
    return timer;
}


@implementation SampleClass {
    dispatch_source_t _timer;
}

- (void)startTimer
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    double secondsToFire = 1.000f;

    _timer = CreateDispatchTimer(secondsToFire, queue, ^{
        // Do something
    });
}

- (void)cancelTimer
{
    if (_timer) {
        dispatch_source_cancel(_timer);
        // Remove this if you are on a Deployment Target of iOS6 or OSX 10.8 and above
        dispatch_release(_timer);
        _timer = nil;
    }
}

@end

```