GCD timer定时器

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); //每秒执行

dispatch_source_set_event_handler(timer, ^{

//@"倒计时结束，关闭"

dispatch_source_cancel(timer);

dispatch_async(dispatch_get_main_queue(), ^{

if (second >= 0) { 

[_getNumBtn setTitle:[NSString stringWithFormat:@"(%ld)重发验证码",second] forState:UIControlStateNormal]; second—; 

} else {

//这句话必须写否则会出问题 dispatch_source_cancel(timer); [_getNumBtn setTitle:@"获取验证码" forState:UIControlStateNormal]; 

}

});

});

dispatch_resume(timer);