如清除中的拉动添加手势

Question

有人能够正确地做到这一点吗？

这是一个涵盖手势http://www.raywenderlich.com/22174/how-to-make-a-gesture-driven-to-do-list-app-part-33的教程。以下是项目文件：https://github.com/ColinEberhardt/iOS-ClearStyle

它远不如原始的Clear应用程序那么顺畅：

#pragma mark - UIScrollViewDelegate methods

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
// this behaviour starts when a user pulls down while at the top of the table
_pullDownInProgress = scrollView.contentOffset.y <= 0.0f;

if (_pullDownInProgress)
{
    // add our placeholder
    [_tableView insertSubview:_placeholderCell atIndex:0];
}
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
if (_pullDownInProgress && _tableView.scrollView.contentOffset.y <= 0.0f)
{
    // maintain the location of the placeholder
    _placeholderCell.frame = CGRectMake(0, - _tableView.scrollView.contentOffset.y - SHC_ROW_HEIGHT,
                                _tableView.frame.size.width, SHC_ROW_HEIGHT);
    _placeholderCell.label.text = -_tableView.scrollView.contentOffset.y > SHC_ROW_HEIGHT ?
                                                @"Release to Add Item" : @"Pull to Add Item";

    _placeholderCell.alpha = MIN(1.0f, - _tableView.scrollView.contentOffset.y / SHC_ROW_HEIGHT);
}
else
{
    _pullDownInProgress = false;
}
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
// check whether the user pulled down far enough
if (_pullDownInProgress && - _tableView.scrollView.contentOffset.y > SHC_ROW_HEIGHT)
{
    [_tableView.datasource itemAdded];
}

_pullDownInProgress = false;
[_placeholderCell removeFromSuperview];
}

@end