Question

我正在编写一个应用程序，它利用UICollectionView在CollectionView Cells中显示一些内容。使用捏合手势，需要重新加载集合视图。我能够根据捏合手势处理内容的变化。现在，在捏手势START上，集合视图需要重新加载并滚动到特定索引。为此，我调用了这样的函数：

[tempCollectionView reloadData];

[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(scrollToItem)  userInfo:nil repeats:YES];

[OR]
[self performSelector:@selector(scrollToItem) withObject:nil afterDelay:0.0];

- (void) scrollToItem 
{
    if (m_selectedCellIndex == -1) 
    {
        NSLog(@"cell return");
        return;
    }

    NSIndexPath *iPath = [NSIndexPath indexPathForItem:m_selectedCellIndex inSection:0];
    [tempLocalFilesCollectionView scrollToItemAtIndexPath:iPath atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:NO];

    LocalFilesCollectionViewCell *cell = (LocalFilesCollectionViewCell *) [m_tempLocalFilesCollectionView cellForItemAtIndexPath: iPath];
    if (cell) 
    {
        CGPoint p = [tempCollectionView convertPoint: cell.center fromView: tempCollectionView];
        NSLog(@"center: %f, %f,  %f, %f", cell.center.x, cell.center.y, p.x, p.y);
    }
    else 
    {
        NSLog(@"Not found");
    }
}

但滚动不起作用。它崩溃时出现错误“尝试滚动到无效索引路径”。很明显，tempCollectionView没有准备好滚动任何单元格。

重新加载完成后如何滚动到索引路径？任何帮助都会很棒!!

Answer 1

试试这个

BOOL _viewDidLayoutSubviewsForTheFirstTime = YES;

- (void)viewDidLoad
{
  [super viewDidLoad];
  _viewDidLayoutSubviewsForTheFirstTime = YES;
}

- (void)viewDidLayoutSubviews
{
  [super viewDidLayoutSubviews];
  // Only scroll when the view is rendered for the first time
  if (_viewDidLayoutSubviewsForTheFirstTime) {
    _viewDidLayoutSubviewsForTheFirstTime = NO;
    // Calling collectionViewContentSize forces the UICollectionViewLayout to actually render the layout
    [self.collectionView.collectionViewLayout collectionViewContentSize];
    // Now you can scroll to your desired indexPath or contentOffset
    [self.collectionView scrollToItemAtIndexPath:yourDesiredIndexPath atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:NO];
  }
}

希望它对某人有帮助

Answer 2

到目前为止，我发现的最佳解决方案是像这样使用CATransaction：

CATransaction.begin()
CATransaction.setCompletionBlock {
    collectionView.scrollToItem(...)
}

collectionView.reloadData()

CATransaction.commit()

Answer 3

如果要滚动垂直

，可以尝试此异步代码

dispatch_async(dispatch_get_main_queue(), ^{
    [_yourCollectionView reloadData];
    [_yourCollectionView reloadInputViews];
    [_yourCollectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:5 inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredVertically animated:YES];
});

并替换为

[_yourCollectionView scrollToItemAtIndexPath:[NSIndexPath indexPathForRow:5 inSection:0] atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];

如果您希望滚动视图滚动水平

将 indexPathForRow 和 inSection 的数量替换为您要滚动到的行号，并记住 NSIndexPath UITableView < / strong>和 UICollectionView 通常附带 inSection 引用Convert NSInteger to NSIndexpath

重新加载并滚动到特定的集合视图单元格

3 个答案: