Question

我有一个UICollectionView。它水平滚动，只有一行项目，行为类似于分页UIScrollView。我正在制作Safari选项卡选项卡的内容，因此您仍然可以看到每个项目的边缘。我只有一个部分。

如果我删除的项目不是最后一项，那么一切都按预期工作，一个新项目从右侧滑入。

如果我删除了最后一项，那么集合视图的滚动位置会跳转到第N-1项（不能平滑地设置动画），然后我会看到第N项（我删除的项）淡出。

此行为与我所做的自定义布局无关，因为即使我将其切换为使用普通流布局也会发生这种情况。我正在删除这些项目：

[self.tabCollectionView deleteItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:index inSection:0]]];

还有其他人经历过这个吗？它是UICollectionView中的错误，是否有解决方法？

Answer 1

我设法使用标准UICollectionViewFlowLayout让我的实施工作。我不得不手动创建动画。

首先，我使用基本动画导致已删除的单元格淡出：

- (void)tappedCloseButtonOnCell:(ScreenCell *)cell {

    // We don't want to close our last screen.
    if ([self screenCount] == 1u) {
        return;
    }

    [UIView animateWithDuration:UINavigationControllerHideShowBarDuration
                     animations:^{
                         // Fade out the cell.
                         cell.alpha = 0.0f;
                     }
                     completion:^(BOOL finished) {

                         NSIndexPath *indexPath = [self.collectionView indexPathForCell:cell];
                         UIViewController *screen = [self viewControllerAtIndex:indexPath.item];

                         [self removeScreen:screen animated:YES];
                     }];
}

接下来，我使集合视图滚动到上一个单元格。一旦我滚动到所需的单元格，我删除已删除的单元格。

- (void)removeScreen:(UIViewController *)screen animated:(BOOL)animated {

    NSParameterAssert(screen);

    NSInteger index = [[self.viewControllerDictionaries valueForKeyPath:kViewControllerKey] indexOfObject:screen];

    if (index == NSNotFound) {
        return;
    }

    [screen willMoveToParentViewController:nil];

    if (animated) {

        dispatch_time_t popTime = DISPATCH_TIME_NOW;
        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:index
                                                 inSection:0];

        // Disables user interaction to make sure the user can't interact with
        // the collection view during the time between when the scroll animation
        // ends and the deleted cell is removed.
        [self.collectionView setUserInteractionEnabled:NO];

        // Scrolls to the previous item, if one exists. If we are at the first
        // item, we just let the next screen slide in from the right.
        if (index > 0) {
            popTime = dispatch_time(DISPATCH_TIME_NOW, 0.5 * NSEC_PER_SEC);
            NSIndexPath *targetIndexPath = [NSIndexPath indexPathForItem:index - 1
                                                  inSection:0];
            [self.collectionView scrollToItemAtIndexPath:targetIndexPath
                                        atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally
                                                animated:YES];
        }

        // Uses dispatch_after since -scrollToItemAtIndexPath:atScrollPosition:animated:
        // doesn't have a completion block.
        dispatch_after(popTime, dispatch_get_main_queue(), ^{

            [self.collectionView performBatchUpdates:^{
                [self.viewControllerDictionaries removeObjectAtIndex:index];
                [self.collectionView deleteItemsAtIndexPaths:@[indexPath]];
                [screen removeFromParentViewController];
                [self.collectionView setUserInteractionEnabled:YES];
            } completion:NULL];
        });

    } else {
        [self.viewControllerDictionaries removeObjectAtIndex:index];
        [self.collectionView reloadData];
        [screen removeFromParentViewController];
    }

    self.addPageButton.enabled = YES;
    [self postScreenChangeNotification];
}

唯一有问题的部分是dispatch_after()。不幸的是，-scrollToItemAtIndexPath:atScrollPosition:animated:没有完成块，所以我不得不模拟它。为了避免计时问题，我禁用了用户交互。这可以防止用户在删除单元格之前与集合视图进行交互。

我需要注意的另一件事是由于细胞重用，我必须将细胞的alpha重置为1。

我希望这可以帮助您使用Safari风格的标签选择器。我知道你的实现与我的不同，我希望我的解决方案也适合你。

Answer 2

我知道这已经有了答案，但是我以稍微不同的方式实现了这一点，在设定的间隔后不需要调度。

在删除方法中，您需要检查以确定是否删除了最后一项。如果是，请拨打以下电话：

if(self.selection == self.assets.count-1 && self.selection != 0){
    isDeleting = YES;
    [collection scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:self.selection-1 inSection:0] atScrollPosition:UICollectionViewScrollPositionLeft animated:YES];
}

假设选择是您要删除的所选项目。这将滚动到它左侧的项目。请注意if语句检查这不是唯一的项目。如果是，那么调用就会崩溃，因为没有-1行。

然后，您可以实现以下方法，该方法在滚动动画完成时调用。我只是在deleteObjectInCollection方法中将isDeleting设置为no，这一切似乎都有效。

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView{
    if(isDeleting){
        [self deleteObjectInCollection];
    }
}

我希望这会有所帮助。

Answer 3

这是另一个解决方案（targetIndexPath是要删除的单元格的indexPath）。这段代码可以简单地放在removeCellAtIndexPath：（NSIndexPath *）targetIndexPath方法中，你已经完成了（假设我从代码到公共代码的修改是正确的，否则请问我，我会尽力帮助）。

// (Here it's assumed that self.collectionView.collectionViewLayout has been assigned a UICollectionViewFlowLayout before; note the word "FLOW" in that class name) 
UICollectionViewFlowLayout* layout = (UICollectionViewFlowLayout*) self.collectionView.collectionViewLayout;

// Find index path of the last cell in collection view:
NSIndexPath* lastIndexPath = [self lastItemIndexPath];

// Extend content area temporarily to fill out space left by the last row after deletion, if last row is visible:
BOOL lastRowWasVisible = NO;
if ([self.collectionView icn_cellAtIndexPathIsVisible:lastIndexPath]) {

    lastRowWasVisible = YES;

    // Adapt section spacing to temporarily fill out the space potentially left after removing last cell:
    CGFloat cellWithLineSpacingHeight = 79.0f + 8.0f; // Height of my cell + one line spacing
    layout.sectionInset = UIEdgeInsetsMake(0.0f, 0.0f, cellWithLineSpacingHeight, 0.0f);
}

// Remove the cell:
[self.collectionView performBatchUpdates:^{

    [self.collectionView deleteItemsAtIndexPaths:[NSArray arrayWithObject:targetIndexPath]];

} completion:^(BOOL finished) {

    // Only scroll if we had the last row visible:
    if (lastRowWasVisible) {

        NSIndexPath* lastItemIndexPath = [self lastItemIndexPath];

        // Run a custom scroll animation for two reasons; 1. that way we can reset the insets when animation is finished, and 2. using the "animated:YES" option lags here for some reason:
        [UIView animateWithDuration:0.3f animations:^{
            [self.collectionView scrollToItemAtIndexPath:prevItemIndexPath atScrollPosition:UICollectionViewScrollPositionBottom animated:NO];
        } completion:^(BOOL finished) {

            // Reset the space placeholder once having scrolled away from it:
            layout.sectionInset = UIEdgeInsetsMake(0.0f, 0.0f, 0.0f, 0.0f);
        }];
    }
}];

icn_cellAtIndexPathIsVisible：方法只是UICollectionView上的一个类别：

- (BOOL) icn_cellAtIndexPathIsVisible:(NSIndexPath*)indexPath {

    BOOL __block wasVisible = NO;
    [self.indexPathsForVisibleItems enumerateObjectsUsingBlock:^(NSIndexPath* ip, NSUInteger idx, BOOL *stop) {

        if ([ip isEqual:indexPath]) {

            wasVisible = YES;
            *stop = YES;
        }
    }];

    return wasVisible;
}

<强>更新这仅适用于一个部分。

Answer 4

一个便宜的解决方案是添加另一个0px单元格作为最后一个单元格，永远不会删除它。

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if let detail = segue.destinationViewController as!  detailSkinsViewController {
           detail.skinNameLabel = self.skin
           if (self.skin == "AK47 | Wasteland Rebel") {
              detail.skinImg.image = UIImage(named: "s495fn")
           }
      }
}

Answer 5

我遇到了类似的问题，单行横向滚动图像集合视图。当我删除用于设置集合视图的代码时，问题就消失了contentSize它似乎自动处理了这个问题。

不是特别冗长的答案，但我希望它有所帮助。

Answer 6

这将有效：

collectionView.collectionViewLayout.invalidateLayout()

collectionView.layoutIfNeeded()

UICollectionView水平滚动，删除最后一项，动画不起作用

6 个答案: