GCD定时器

代码：

@interface ViewController ()

@property (nonatomic, strong) dispatch_source_t timer;

@end

@implementation ViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    dispatch_queue_t dispatchQueue = dispatch_get_main_queue();
    // dispatch_source_t本质是一个OC对象
    dispatch_source_t timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, dispatchQueue);
    dispatch_time_t start = DISPATCH_TIME_NOW;
    uint64_t interval = 1 * NSEC_PER_SEC;
    uint64_t leeway = 0 * NSEC_PER_SEC;
    dispatch_source_set_timer(timer, start, interval, leeway);
    dispatch_block_t _Nullable handler = ^void(void) {
        // code...
    };
    dispatch_source_set_event_handler(timer, handler);
    dispatch_resume(timer);
    self.timer = timer;
}

@end