有时候，滑动视图分页很难伺候

#pragma mark - 手动配置cell居中

- (void)fixCellToCenter {

    //最小滚动距离

    floatdragMiniDistance =SCREEN_WIDTH/20.0f;

    if(_dragStartX-  _dragEndX>= dragMiniDistance) {

        _selectedIndex -= 1;//向右

    }elseif(_dragEndX-  _dragStartX>= dragMiniDistance){

        _selectedIndex += 1;//向左

    }

    NSIntegermaxIndex = [_soreceListViewnumberOfItemsInSection:0] -1;

    _selectedIndex = _selectedIndex <= 0 ? 0 : _selectedIndex;

    _selectedIndex = _selectedIndex >= maxIndex ? maxIndex : _selectedIndex;

    [self scrollToCenter];

}

//滚动到中间

- (void)scrollToCenter {

    [_soreceListView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:_selectedIndex inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];

}

//手指拖动开始

- (void)scrollViewWillBeginDragging:(UIScrollView*)scrollView {

    _dragStartX= scrollView.contentOffset.x;

}

//手指拖动停止

- (void)scrollViewDidEndDragging:(UIScrollView*)scrollView willDecelerate:(BOOL)decelerate {

    _dragEndX= scrollView.contentOffset.x;

    dispatch_async(dispatch_get_main_queue(), ^{

        [self fixCellToCenter];

    });

}