上面vojtech-vrbka的解决方案是正确的，但它会触发一个警告:

警告:UICollectionViewFlowLayout缓存的帧不匹配索引路径-缓存值:这可能是因为流布局子类layout是修改UICollectionViewFlowLayout返回的属性而没有复制它们

下面的代码应该修复它:

class CustomViewFlowLayout : UICollectionViewFlowLayout {

   let cellSpacing:CGFloat = 4

   override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
       let original = super.layoutAttributesForElementsInRect(rect)

       if let original = original {
           let attributes = NSArray.init(array: original, copyItems: true) as! [UICollectionViewLayoutAttributes]

           for (index, attribute) in attributes.enumerate() {
                if index == 0 { continue }
                let prevLayoutAttributes = attributes[index - 1]
                let origin = CGRectGetMaxX(prevLayoutAttributes.frame)
                if(origin + cellSpacing + attribute.frame.size.width < self.collectionViewContentSize().width) {
                    attribute.frame.origin.x = origin + cellSpacing
                }
            }
            return attributes
       }
       return nil
   }
}

试试下面的代码，确保每个项目之间的间距为5px:

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

    return UIEdgeInsetsMake(0, 0, 0, 5); // top, left, bottom, right
}

- (CGFloat)collectionView:(UICollectionView *) collectionView
                   layout:(UICollectionViewLayout *) collectionViewLayout
  minimumInteritemSpacingForSectionAtIndex:(NSInteger) section {    
    return 5.0;
}

使用水平流布局，我也得到了10点之间的单元格间距。为了移除间距，我需要将minimumlinespespaces和minimumInterItemSpacing设置为零。

UICollectionViewFlowLayout *flow = [[UICollectionViewFlowLayout alloc] init];
flow.itemSize = CGSizeMake(cellWidth, cellHeight);
flow.scrollDirection = UICollectionViewScrollDirectionHorizontal;
flow.minimumInteritemSpacing = 0;
flow.minimumLineSpacing = 0;

此外，如果所有单元格大小相同，直接在流布局上设置属性比使用委托方法更简单、更有效。

最流行的答案的Swift版本。单元格之间的空格将等于cellSpacing。

class CustomViewFlowLayout : UICollectionViewFlowLayout {

    let cellSpacing:CGFloat = 4

    override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
        if let attributes = super.layoutAttributesForElementsInRect(rect) {
        for (index, attribute) in attributes.enumerate() {
                if index == 0 { continue }
                let prevLayoutAttributes = attributes[index - 1]
                let origin = CGRectGetMaxX(prevLayoutAttributes.frame)
                if(origin + cellSpacing + attribute.frame.size.width < self.collectionViewContentSize().width) {
                    attribute.frame.origin.x = origin + cellSpacing
                }
            }
            return attributes
        }
        return nil
    }
}

投票的答案(以及快速版本)有一个小问题:右边会有一个很大的空格。

这是因为流布局是定制的，以使单元格间距精确，具有浮动左行为。

我的解决方案是操纵部分插入，使部分是对齐中心，但间距是完全指定的。

在下面的截图中，项目/行间距正好是8pt，而左右插入部分将大于8pt(使其居中对齐):

这样的Swift代码:

private let minItemSpacing: CGFloat = 8
private let itemWidth: CGFloat      = 100
private let headerHeight: CGFloat   = 32

override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    // Create our custom flow layout that evenly space out the items, and have them in the center
    let layout = UICollectionViewFlowLayout()
    layout.itemSize = CGSize(width: itemWidth, height: itemWidth)
    layout.minimumInteritemSpacing = minItemSpacing
    layout.minimumLineSpacing = minItemSpacing
    layout.headerReferenceSize = CGSize(width: 0, height: headerHeight)

    // Find n, where n is the number of item that can fit into the collection view
    var n: CGFloat = 1
    let containerWidth = collectionView.bounds.width
    while true {
        let nextN = n + 1
        let totalWidth = (nextN*itemWidth) + (nextN-1)*minItemSpacing
        if totalWidth > containerWidth {
            break
        } else {
            n = nextN
        }
    }

    // Calculate the section inset for left and right. 
    // Setting this section inset will manipulate the items such that they will all be aligned horizontally center.
    let inset = max(minItemSpacing, floor( (containerWidth - (n*itemWidth) - (n-1)*minItemSpacing) / 2 ) )
    layout.sectionInset = UIEdgeInsets(top: minItemSpacing, left: inset, bottom: minItemSpacing, right: inset)

    collectionView.collectionViewLayout = layout
}

间距的简单代码

let layout = collectionView.collectionViewLayout as! UICollectionViewFlowLayout
layout.minimumInteritemSpacing = 10 // Some float value