UiTableView 标题没有消失 [英] UiTableView header not disappearing

问题描述

我有一个 UITableView 配置为普通样式，所以我可以将标题视图卡在表格顶部，直到另一个标题将其拉走.

I have a UITableView configured as plain style so I can have the header views stuck on the top of the table until another header pulls it away.

问题是:如果我有一个标题卡在屏幕顶部，并且我以编程方式滚动到表格的另一部分(该标题根本不应该出现在那里)，则 UIView 不会被关闭.IE.如果我再次滚动到表格的那部分，表格的那部分上就会看到那个标题的影子.

The problem is: If I have a header stuck on the top of the screen, and I programmatically scroll to another part of the table (where that header should not appear at all), that UIView will not be dismissed. I.e. if I scroll again to that part of the table, a ghost of that header will be visible on that part of the table.

我已经实现了方法 - (void)tableView:(UITableView *)tableView didEndDisplayingHeaderView:(nonnull UIView *)view forSection:(NSInteger)section 以了解发生了什么.我发现如果我手动滚动直到标题被拉离屏幕，这个委托就会被调用.但是如果我以编程方式滚动，则不会调用委托.

I've implemented the method - (void)tableView:(UITableView *)tableView didEndDisplayingHeaderView:(nonnull UIView *)view forSection:(NSInteger)section to understand what is happening. I found that if I manually scroll until a header is pull away of the screen, this delegate is called. But if I scroll programmatically, the delegate is not called.

顺便说一下，我尝试使用两种不同的方法以编程方式滚动，问题是一样的.

By the way, I tried scrolling programmatically using two different methods, and the problem is the same.

- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated;
- (void)scrollToRowAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UITableViewScrollPosition)scrollPosition animated:(BOOL)animated;

我可以想象的一种解决方法是实现 - (void)scrollViewDidScroll:(UIScrollView *)scrollView;，过滤可见屏幕之外的所有标题视图，并将它们从超级视图中删除.我可能可以让它工作，但我想知道是否有其他更好的解决方案.

One workaround that I can imagine is implementing - (void)scrollViewDidScroll:(UIScrollView *)scrollView;, filtering all the header views that are outside the visible screen, and removing them from superview. I can probably make it work, but I would like to know if there is any other better solution.

如果我调用 - (void)setContentOffset:(CGPoint)contentOffset animation:(BOOL)animated; 和 animation = YES，错误不会发生.我可以使用这个解决方案，但在某些情况下我真的希望在没有动画的情况下滚动.

If I call - (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated; with animated = YES, the bug does not happen. I can go with this solution, but I really would like in some cases to scroll without animation.

推荐答案

TL;DR

不要在beginUpdates 和endUpdates 之间显式滚动表格视图.

Do NOT explicitly scroll the table view between beginUpdates and endUpdates.

说明

我使用 NSFetchedResultsController 来填充表格.这些是我对 NSFetchedResultsControllerDelegate 的一些方法的实现.

I'm using NSFetchedResultsController to populate the table. These are my implementations for some of the methods of NSFetchedResultsControllerDelegate.

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [_conversationTableView beginUpdates];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [_conversationTableView endUpdates];
}

问题是 endUpdates 进行了一系列调用，最终调用了我的方法 [self scrollToBottom] (实际上这是一个非常丑陋的代码).顾名思义，这个方法调用 - (void)setContentOffset:(CGPoint)contentOffset animation:(BOOL)animated; 将表格视图滚动到表格底部.

The problem is that endUpdates was making a chain of calls that ended calling my method [self scrollToBottom] (which was a very ugly code actually). This method, as the name says, calls - (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated; to scroll the table view to the bottom of the table.

在 beginUpdates - endUpdates 期间显式滚动表格是我整个问题的罪魁祸首.

The explicit scrolling of the table during a beginUpdates - endUpdates was the culprit of my whole problem.

解决方案

仅在完成 ​​endUpdates 后滚动表格视图.

Scrolling the table view only after finishing endUpdates.

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    [_conversationTableView beginUpdates];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    [_conversationTableView endUpdates];

    [self scrollToBottom];
}

旁注

这也解决了滚动时表格视图有时闪烁的问题.

This also fixed a problem where the table view was sometimes flickering when scrolling.

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