如何确定 UICollectionView flowLayout 中单元格之间的间距

我有一个带有流布局的 UICollectionView，每个单元格都是一个正方形。如何确定每行中每个单元格之间的间距？我似乎找不到合适的设置。我看到集合视图的 nib 文件上有一个最小间距属性，但我将其设置为 0 并且单元格甚至不粘在一起。

还有其他想法吗？

更新：这个答案的 Swift 版本：https://github.com/fanpyi/UICollectionViewLeftAlignedLayout-Swift https://github.com/fanpyi/UICollectionViewLeftAlignedLayout-Swift

Taking @matt 的领导 https://stackoverflow.com/a/13258495/250190我修改了他的代码以确保项目始终左对齐。我发现，如果一个项目本身位于一行，它将以流布局为中心。我做了以下更改来解决这个问题。

仅当单元格宽度不同时才会发生这种情况，这可能会导致如下所示的布局。由于以下行为，最后一行始终左对齐UICollectionViewFlowLayout，问题在于除最后一项之外的任何行中单独存在的项目。

通过@matt的代码我看到了。

在该示例中，我们看到如果单元格最终单独在线上，则单元格会居中。下面的代码确保您的集合视图看起来像这样。

#import "CWDLeftAlignedCollectionViewFlowLayout.h"

const NSInteger kMaxCellSpacing = 9;

@implementation CWDLeftAlignedCollectionViewFlowLayout

- (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];

    CGRect currentFrame = currentItemAttributes.frame;

    if (indexPath.item == 0) { // first item of section
        currentFrame.origin.x = sectionInset.left; // first item of the section should always be left aligned
        currentItemAttributes.frame = currentFrame;

        return currentItemAttributes;
    }

    NSIndexPath* previousIndexPath = [NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section];
    CGRect previousFrame = [self layoutAttributesForItemAtIndexPath:previousIndexPath].frame;
    CGFloat previousFrameRightPoint = CGRectGetMaxX(previousFrame) + kMaxCellSpacing;

    CGRect strecthedCurrentFrame = CGRectMake(0,
                                              currentFrame.origin.y,
                                              self.collectionView.frame.size.width,
                                              currentFrame.size.height);

    if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) { // if current item is the first item on the line
        // the approach here is to take the current frame, left align it to the edge of the view
        // then stretch it the width of the collection view, if it intersects with the previous frame then that means it
        // is on the same line, otherwise it is on it's own new line
        currentFrame.origin.x = sectionInset.left; // first item on the line should always be left aligned
        currentItemAttributes.frame = currentFrame;
        return currentItemAttributes;
    }

    currentFrame.origin.x = previousFrameRightPoint;
    currentItemAttributes.frame = currentFrame;
    return currentItemAttributes;
}

@end