ios - UICollectionViewFlowLayout 忽略不同高度项目的部分插图 - 错误还是预期？

Question

我正在使用 UICollectionViewFlowLayout 并想像下面那样应用部分插图。我所有的元素都具有相同的宽度但高度不同。当同一部分中的项目高度相同时，插图有效，但当它们在同一部分中的高度不同时，则无效。这是此布局的预期行为吗？我是否需要子类化并定制一个或缺少某些东西？

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {

    UIEdgeInsets insets = UIEdgeInsetsZero;

    CGFloat big = 30;
    CGFloat small = 10;

    if (section < 5) {
        insets = UIEdgeInsetsMake(0, big, 0, small);
    } else {
        insets = UIEdgeInsetsMake(0, small, 0, big);
    }

    return insets;
}

Answer 1

出于某种原因，如果您每行有一个项目，UICollectionViewFlowLayout 具有将单元格居中的行为。它会忽略插入的部分。

您可以通过覆盖 UICollectionViewFlowLayout 并更改以下两个方法来解决此问题:

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes *attribute = [super layoutAttributesForItemAtIndexPath:indexPath];

    [self fixLayoutAttributeInsets:attribute];

    return attribute;
}

和

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray *results = [super layoutAttributesForElementsInRect:rect];

    for (UICollectionViewLayoutAttributes *attribute in results)
    {
        [self fixLayoutAttributeInsets:attribute];
    }

    return results;
}

魔法:

- (void)fixLayoutAttributeInsets:(UICollectionViewLayoutAttributes *)attribute
{
    if ([attribute representedElementKind])
    { //nil means it is a cell, we do not want to change the headers/footers, etc
        return;
    }

    //Get the correct section insets
    UIEdgeInsets sectionInsets;

    if ([[[self collectionView] delegate] respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)])
    {
        sectionInsets = [(id<UICollectionViewDelegateFlowLayout>)[[self collectionView] delegate] collectionView:[self collectionView] layout:self insetForSectionAtIndex:[[attribute indexPath] section]];
    }
    else
    {
        sectionInsets = [self sectionInset];
    }

    //Adjust the x position of the view, the size should be correct or else do more stuff here
    CGRect frame = [attribute frame];

    frame.origin.x = sectionInsets.left;

    [attribute setFrame:frame];
}

如果您在一行中有多个单元格，则此解决方案不起作用(也不需要)，因此您应该使用 bool 值或任何您喜欢的方式检查这种情况...这只是此场景的一个简单示例