问题描述
给定一个在任何给定时间带有单个可见单元格的 UITableView，如何在滚动表格视图时确定哪个单元格最?
Given a UITableView with a single visible cell at any given time, how can I determine which cell is most in view while the table view is being scrolled?
我知道我可以通过这样做获得一组可见的单元格:
I know I can get an array of visible cells by doing this:
NSArray *paths = [tableView indexPathsForVisibleRows];
然后通过执行以下操作获取最后一个单元格(或第一个，或其他):
And then get the last cell (or first, or whatever) by doing:
UITableViewCell* cell = (UITableViewCell*)[tableView cellForRowAtIndexPath:[paths lastObject]];
但是如何比较所有可见的单元格并确定它们中的哪一个最能看到?
But how to I compare all the visible cells and determine which of them is most in view?
推荐答案
算法根据返回的路径数而有所不同:
The algorithm is different depending on how many paths you get back:
- 如果只有一条路径，那就是那里最明显的单元格
- 如果存在三个或更多路径，则中间的任何单元格(即除第一个和最后一个单元格之外的所有单元格)同样可见
- 如果正好有两个单元格，则在它们的父视图中找到分隔这两个单元格的线的位置，并计算两个距离 - 顶部到中间和中间到底部.如果从上到中更大，则顶部单元格最明显.如果中间到底部更大，则第二个单元格更明显.否则，两个单元格同样可见.
- If there is only one path, that's the most visible cell right there
- If there are three or more paths, any of the cells in the middle (i.e. all cells except the first and the last ones) are equally visible
- If there are exactly two cells, find the position of the line that separates the two in their parent view, and compute two distances - top-to-middle and middle-to-bottom. If top-to-middle is greater, then the top cell is most visible. If middle-to-bottom is greater, then the second cell is more visible. Otherwise, the two cells are equally visible.
中点位置是第二个单元格的底部.顶部和底部位置是表格视图的顶部和底部.
Midpoint position is the bottom of the second cell. Top and bottom positions are the top and bottom of the table view.
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