ios - 你如何垂直对齐 UICollectionView 中的 UICollectionViewCells？

Question

我在水平滚动上有不同高度的单元格，UICollectionView它似乎垂直地均匀分布单元格，在单元格之间留下空白空间，我想将它们顶部对齐并在每列的底部有可变的空白空间。

Answer 1

我扩展了提供给我的 UICollectionView 的 UICollectionViewFlowLayout。以下覆盖对我有用。

#import "TopAlignedCollectionViewFlowLayout.h"

const NSInteger kVerticalSpacing = 10;

@implementation TopAlignedCollectionViewFlowLayout

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
    NSArray* attributesToReturn = [super layoutAttributesForElementsInRect:rect];
    for (UICollectionViewLayoutAttributes* attributes in attributesToReturn) {
        if (nil == attributes.representedElementKind) {
            NSIndexPath* indexPath = attributes.indexPath;
            attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
        }
    }
    return attributesToReturn;
}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes* currentItemAttributes =
    [super layoutAttributesForItemAtIndexPath:indexPath];
    UIEdgeInsets sectionInset = [(UICollectionViewFlowLayout *)self.collectionView.collectionViewLayout sectionInset];
    if (indexPath.item == 0) { 
        CGRect frame = currentItemAttributes.frame;
        frame.origin.y = sectionInset.top;
        currentItemAttributes.frame = frame;

        return currentItemAttributes;
    }
    NSIndexPath* previousIndexPath = [NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section];
    CGRect previousFrame = [self layoutAttributesForItemAtIndexPath:previousIndexPath].frame;
    CGFloat previousFrameRightPoint = previousFrame.origin.y + previousFrame.size.height + kVerticalSpacing;
    CGRect currentFrame = currentItemAttributes.frame;
    CGRect strecthedCurrentFrame = CGRectMake(currentFrame.origin.x,
                                              0,
                                              currentFrame.size.width,
                                              self.collectionView.frame.size.height
                                              );
    if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) {
        CGRect frame = currentItemAttributes.frame;
        frame.origin.y = frame.origin.y = sectionInset.top;
        currentItemAttributes.frame = frame;
        return currentItemAttributes;
    }
    CGRect frame = currentItemAttributes.frame;
    frame.origin.y = previousFrameRightPoint;
    currentItemAttributes.frame = frame;
    return currentItemAttributes;
}

@end

Answer 2

我将此移植到 Xamarin/MonoTouch 用于我的项目，并认为它可能有用

public class TopAlignedCollectionViewFlowLayout : UICollectionViewFlowLayout
{
    const int VerticalSpacing = 10;

    public override UICollectionViewLayoutAttributes[] LayoutAttributesForElementsInRect(RectangleF rect)
    {
        var attributesToReturn = base.LayoutAttributesForElementsInRect(rect);
        foreach (UICollectionViewLayoutAttributes attributes in attributesToReturn)
        {
            if (attributes.RepresentedElementKind == null)
            {
                var indexPath = attributes.IndexPath;
                attributes.Frame = this.LayoutAttributesForItem(indexPath).Frame;
            }
        }
        return attributesToReturn;
    }

    public override UICollectionViewLayoutAttributes LayoutAttributesForItem(NSIndexPath indexPath)
    {
        var currentItemAttributes = base.LayoutAttributesForItem(indexPath);
        UIEdgeInsets sectionInset = ((UICollectionViewFlowLayout) this.CollectionView.CollectionViewLayout).SectionInset;

        if (indexPath.Item == 0)
        {
            var frame1 = currentItemAttributes.Frame;
            frame1.Y = sectionInset.Top;
            currentItemAttributes.Frame = frame1;

            return currentItemAttributes;
        }

        var previousIndexPath = NSIndexPath.FromItemSection(indexPath.Item - 1, indexPath.Section);
        var previousFrame = this.LayoutAttributesForItem(previousIndexPath).Frame;
        var previousFrameRightPoint = previousFrame.Y + previousFrame.Size.Height + VerticalSpacing;
        var currentFrame = currentItemAttributes.Frame;
        var strecthedCurrentFrame = new RectangleF(currentFrame.X, 0, currentFrame.Size.Width, this.CollectionView.Frame.Size.Height);
        if (!previousFrame.IntersectsWith(strecthedCurrentFrame))
        {
            var frame = currentItemAttributes.Frame;
            frame.Y = frame.Y = sectionInset.Top;
            currentItemAttributes.Frame = frame;
            return currentItemAttributes;
        }
        RectangleF frame2 = currentItemAttributes.Frame;
        frame2.Y = previousFrameRightPoint;
        currentItemAttributes.Frame = frame2;
        return currentItemAttributes;
    }

}

Answer 3

我想你正在使用 UICollectionViewFlowLayout 来布局你的单元格。我不认为你可以用流布局来做到这一点。您可能必须编写 UICollectionViewLayout 的自定义子类来对齐每个单元格的顶部边缘。

这不是一个非常漂亮的解决方案，但是如何强制所有单元格大小相同并在单元格中设置约束以将内容与顶部对齐？这可以模拟您想要的外观，而无需继承 UICollectionViewLayout。