检测 UITableViewCell 何时离开屏幕 [英] Detect when UITableViewCell goes off the screen

问题描述

我正在使用自定义创建的 UITableViewCell 实现丰富的 UITableView，我以一种方式在屏幕上显示它们，但是一旦它们离开屏幕，我想记下这一点，因为它们第二次出现时我会喜欢它们以不同的方式显示.离开屏幕时考虑自动标记为已读".

I'm implementing a rich UITableView with custom created UITableViewCell, I show these on the screen in one fashion, but once they go off the screen I want to take a note of that, since the second time they come on I would like them to get displayed in a different manner. Think auto "mark as read" when going off the screen.

我一直在寻找某种方法来检测单元格何时离开屏幕(被解除分配或出队或等效)，最好在 :UITableViewController 类中快速记下 [indexPath 行]，但是在 :UITableViewCell 中也一样好.

I've been looking for some way to detect when a cell goes off the screen (get's dealloc'ed or dequeued or equivalent), preferably in the :UITableViewController class to make a quick note of the [indexPath row], but in the :UITableViewCell is equally as good.

我无法以任何标准方式做到这一点......计算它出现的次数似乎是不可能的，因为我在桌子上进行了多次 reloadData 调用.

I haven't been able to do this in any standard way ... counting the times it appeared seems out of the question as I do multiple reloadData calls on the table.

有人有什么想法吗?这似乎有点棘手:)

Anyone any ideas? This seems a bit tricky :)

推荐答案

这是一个老问题，但以防万一有人在看，在 iOS6 中，引入了一个新的 UITableViewDelegate 函数来做到这一点:

This is an old question, but in case anyone is looking, in iOS6, a new UITableViewDelegate function was introduced that does just this:

- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath

它在告诉您何时删除单元格方面做得很好，但是，它非常彻底，因此如果您重新加载单元格，即使正在替换的旧单元格也会触发此委托函数.在我的实现中，我只是检查传递的 indexPath 是否仍在数组 tableView.indexPathsForVisibleRows 中.类似的东西:

It does a great job at telling you whenever a cell is removed, however, it is very thorough and thus if you did a reload cell, even the old cell that's being replaced will trigger this delegate function. In my implementation I simply check to see if the indexPath passed is still within the array tableView.indexPathsForVisibleRows. Something like:

- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
    if ([tableView.indexPathsForVisibleRows indexOfObject:indexPath] == NSNotFound)
    {
        // This indeed is an indexPath no longer visible
        // Do something to this non-visible cell...
    }
}

这篇关于检测 UITableViewCell 何时离开屏幕的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！