ios开发之倒计时实现的两种方法

secondsCountDown = 60;//60秒倒计时
 countDownTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timeFireMethod) userInfo:nil repeats:YES];
-(void)timeFireMethod{
    secondsCountDown--;
    if(secondsCountDown==0){
      [countDownTimer invalidate];
    }
}

__block int timeout=300; //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_release(_timer);
        dispatch_async(dispatch_get_main_queue(), ^{
    //设置界面的按钮显示 根据自己需求设置
            。。。。。。。。
        });
    }else{
        int minutes = timeout / 60;
        int seconds = timeout % 60;
        NSString *strTime = [NSString stringWithFormat:@"%d分%.2d秒后重新获取验证码",minutes, seconds];
        dispatch_async(dispatch_get_main_queue(), ^{
            //设置界面的按钮显示 根据自己需求设置
    。。。。。。。。
        });
        timeout--;
 
    }
});
dispatch_resume(_timer);