iOS开发～获取验证码倒计时实现

@property(strong,nonatomic)UIButton *againBtn;

//获取验证码按钮
self.againBtn = [[UIButton alloc]initWithFrame:CGRectMake(SCREEN_WIDTH*2/3-35, 0, SCREEN_WIDTH/3+20, 50)];
   [_againBtn addTarget:self action:@selector(againBtn:) forControlEvents:UIControlEventTouchUpInside];
   self.againBtn.userInteractionEnabled = NO;
   [self messageTime];
   [_againBtn setTitleColor:ALLTextColor forState:0];
   [self.contentView addSubview:_againBtn];

- (void)againBtn:(UIButton *)sender{
   //倒计时函数
   [self messageTime];
}

- (void)messageTime {   __block int timeout=60; //倒计时时间
   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, ^{
       if(timeout<=0){ //倒计时结束，关闭
           dispatch_source_cancel(_timer);
           dispatch_async(dispatch_get_main_queue(), ^{
               //设置界面的按钮显示 根据自己需求设置
               [self.againBtn setTitle:@"发送验证码" forState:UIControlStateNormal];
               [_againBtn setTitleColor:[UIColor blackColor] forState:0];
               self.againBtn.userInteractionEnabled = YES;
           });
       }else{
           int seconds = timeout % 61;
           NSString *strTime = [NSString stringWithFormat:@"%.2d", seconds];
           dispatch_async(dispatch_get_main_queue(), ^{
               //设置界面的按钮显示 根据自己需求设置
               [UIView beginAnimations:nil context:nil];
               [UIView setAnimationDuration:1];
               [self.againBtn setTitle:[NSString stringWithFormat:@"(%@)重新发送",strTime] forState:UIControlStateNormal];
               [_againBtn setTitleColor:ALLTextColor forState:0];
               //To do
               [UIView commitAnimations];
               self.againBtn.userInteractionEnabled = NO;
           });
           timeout--;
       }
   });
   dispatch_resume(_timer);
   
}