在swift中使用UICollectionView粘性标头

问题描述：

我正在尝试创建一个粘性补充标头，它始终保持在顶部并且不会响应滚动事件。到目前为止我发现的解决方案仍然对bounch滚动做出反应并使用自定义flowlayout进行修复，这可能也是我的问题的解决方案。

I'm trying to create a sticky supplementary header, which stays in top all the time and wont response to scrolling events. The solutions I found so far still react on bounch scrolling and are fixed using a custom flowlayout, which will probably be the fix for mine issue as well.

我想要的原因这样，标题是在其他地方使用，应该是可重用的。我希望这可以通过这种方式解决，我不必创建一个单独的视图。

The reason I want it this way, is that the header is used on other places and should be reusable. I'm hoping this could be solved this way and I don't have to create a separated view.

正如我在Swift中这样做的，它会很棒在Swift中有一个例子。

As I'm doing this in Swift, it would be great to have an example in Swift.

答

我找到的最终解决方案：

使用此自定义流布局可以修复此粘性标题：

Using this custom flow layout it was possible to fix this sticky header:

class StickyHeaderCollectionViewFlowLayout: UICollectionViewFlowLayout {

    override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {

        var superAttributes: [UICollectionViewLayoutAttributes]? = super.layoutAttributesForElementsInRect(rect) as? [UICollectionViewLayoutAttributes]

        if superAttributes == nil {
            // If superAttributes couldn't cast, return
            return super.layoutAttributesForElementsInRect(rect)
        }

        let contentOffset = collectionView!.contentOffset
        var missingSections = NSMutableIndexSet()

        for layoutAttributes in superAttributes! {
            if (layoutAttributes.representedElementCategory == .Cell) {
                if let indexPath = layoutAttributes.indexPath {
                    missingSections.addIndex(layoutAttributes.indexPath.section)
                }
            }
        }

        for layoutAttributes in superAttributes! {
            if let representedElementKind = layoutAttributes.representedElementKind {
                if representedElementKind == UICollectionElementKindSectionHeader {
                    if let indexPath = layoutAttributes.indexPath {
                        missingSections.removeIndex(indexPath.section)
                    }
                }
            }
        }

        missingSections.enumerateIndexesUsingBlock { idx, stop in
            let indexPath = NSIndexPath(forItem: 0, inSection: idx)
            if let layoutAttributes = self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: indexPath) {
                superAttributes!.append(layoutAttributes)
            }
        }

        for layoutAttributes in superAttributes! {
            if let representedElementKind = layoutAttributes.representedElementKind {
                if representedElementKind == UICollectionElementKindSectionHeader {
                    let section = layoutAttributes.indexPath!.section
                    let numberOfItemsInSection = collectionView!.numberOfItemsInSection(section)

                    let firstCellIndexPath = NSIndexPath(forItem: 0, inSection: section)!
                    let lastCellIndexPath = NSIndexPath(forItem: max(0, (numberOfItemsInSection - 1)), inSection: section)!


                    let (firstCellAttributes: UICollectionViewLayoutAttributes, lastCellAttributes: UICollectionViewLayoutAttributes) = {
                        if (self.collectionView!.numberOfItemsInSection(section) > 0) {
                            return (
                                self.layoutAttributesForItemAtIndexPath(firstCellIndexPath),
                                self.layoutAttributesForItemAtIndexPath(lastCellIndexPath))
                        } else {
                            return (
                                self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionHeader, atIndexPath: firstCellIndexPath),
                                self.layoutAttributesForSupplementaryViewOfKind(UICollectionElementKindSectionFooter, atIndexPath: lastCellIndexPath))
                        }
                        }()

                    let headerHeight = CGRectGetHeight(layoutAttributes.frame)
                    var origin = layoutAttributes.frame.origin

                    origin.y = min(contentOffset.y, (CGRectGetMaxY(lastCellAttributes.frame) - headerHeight))
                    // Uncomment this line for normal behaviour:
                    // origin.y = min(max(contentOffset.y, (CGRectGetMinY(firstCellAttributes.frame) - headerHeight)), (CGRectGetMaxY(lastCellAttributes.frame) - headerHeight))

                    layoutAttributes.zIndex = 1024
                    layoutAttributes.frame = CGRect(origin: origin, size: layoutAttributes.frame.size)
                }
            }
        }

        return superAttributes
    }

    override func shouldInvalidateLayoutForBoundsChange(newBounds: CGRect) -> Bool {
        return true
    }

}

要像传统一样创建标题粘贴的布局，请更改此行：

To create a layout where the headers are sticky like traditional, change this line:

origin.y = min(contentOffset.y, (CGRectGetMaxY(lastCellAttrs.frame) - headerHeight))

到此行：

origin.y = min(max(contentOffset.y, (CGRectGetMinY(firstCellAttrs.frame) - headerHeight)), (CGRectGetMaxY(lastCellAttrs.frame) - headerHeight))

希望这对其他人有用！

更新

更新以修复崩溃（感谢Robert Atkins！）和Swift 1.2的一些更新

Updated to fix a crash (thanks to Robert Atkins!) and some updates to Swift 1.2

tvOS& iOS 9

tvOS和iOS 9引入了属性 sectionHeadersPinToVisibleBounds 可以使用

tvOS and iOS 9 introduced the property sectionHeadersPinToVisibleBounds which can be used

在swift中使用UICollectionView粘性标头

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