#pragma mark - timer
//创建timer 并开启timer
- (void)creatTimer{
    if (!_timer) {
        //保证timer只被开启一次
        _timer = [NSTimer scheduledTimerWithTimeInterval:_time target:self selector:@selector(action_time) userInfo:nil repeats:YES];
    }
}
-(void)action_time{
    [self.scrollView setContentOffset:CGPointMake(2 * swidth, 0) animated:YES];
}
//开启timer
- (void)starTimer{
    _timer.fireDate = [NSDate dateWithTimeIntervalSinceNow:2];//在现在的时间上加2秒，开始。
}
//暂停timer
- (void)pauseTimer{
    _timer.fireDate = [NSDate distantFuture];
}
//停止timer
- (void)stopTimer{
    [_timer invalidate];
    _timer = nil;
}