- (void)startCountDownAction{
//开始倒计时 codebtn 是发送验证码的btn ，也是倒计时的UI
self.codeBttn.enabled = NO;
__block int timeout = 60;
[self.codeBttn setTitle:@"60秒" forState:UIControlStateNormal];
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(), ^{
//倒计时结束
self.codeBttn.enabled = YES;
[self.codeBttn setTitle:@"发送验证码" forState:UIControlStateNormal];
});
}else{
int seconds = timeout % 60;
NSString *strTime = [NSString stringWithFormat:@"%.2d秒",seconds];
dispatch_async(dispatch_get_main_queue(), ^{
[self.codeBttn setTitle:strTime forState:UIControlStateNormal];
});
timeout--;
}
});
dispatch_resume(_timer);
}
原文：http://www.cnblogs.com/wangxiaorui/p/5484565.html