iOS获取验证码倒计时效果

/**重新发送短信的计时*/-(void)fireTimer{ __block int timeout=180; //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    [_changeCodeButton setTitle:@"获取验证码" forState:UIControlStateNormal];    _changeCodeButton.userInteractionEnabled = YES;   });  }else{   int seconds = timeout ;//% 60;   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    //NSLog(@"____%@",strTime);    [UIView beginAnimations:nil context:nil];    [UIView setAnimationDuration:1];    _changeCodeButton.titleLabel.font = [UIFont systemFontOfSize:14];    [_changeCodeButton setTitle:[NSString stringWithFormat:@"(%@s)后重新获取",strTime] forState:UIControlStateNormal];    [UIView commitAnimations];    _changeCodeButton.userInteractionEnabled = NO;   });   timeout--;  } }); dispatch_resume(_timer);}