iOS 定时器(发送短信验证)

//倒计时
- (void)startTimer {
__block int timeout = 59;
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_source_t _timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0,queue);
dispatch_source_set_timer(_timer, dispatch_walltime(NULL, 0), 1.0 * NSEC_PER_SEC, 0);
dispatch_source_set_event_handler(_timer, ^{
if (timeout <= 0) {
dispatch_source_cancel(_timer);
dispatch_async(dispatch_get_main_queue(), ^{
UIButton *button = (UIButton *)[self.view viewWithTag:50];
button.alpha = 1.0;
button.userInteractionEnabled = YES;
self.reGetCodeLabel.text = @"59s后重新获取";
});
} else {
int second = timeout % 60;
dispatch_async(dispatch_get_main_queue(), ^{
UIButton *button = (UIButton *)[self.view viewWithTag:50];
button.userInteractionEnabled = NO;
button.alpha = 0.5;
self.reGetCodeLabel.text = [NSString stringWithFormat:@"%ds后重新获取", second];
});
timeout--;
}
});
dispatch_resume(_timer);
}