我试图修改UICollectionViewFlowLayout(垂直滚动),以便将每个节标题放在该节的所有项目的左侧(而不是在顶部,这是默认值).
也就是说,这是默认行为:
……这就是我想要的:
所以我将UICollectionViewFlowLayout子类化:
override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard let attributesToReturn = super.layoutAttributesForElementsInRect(rect) else {
return nil
}
// Copy to avoid the dreadded "Cached frame mismatch" runtime warning:
var copiedAttributes = [UICollectionViewLayoutAttributes]()
for attribute in attributesToReturn {
copiedAttributes.append(attribute.copy() as! UICollectionViewLayoutAttributes)
}
for attributes in copiedAttributes {
if let kind = attributes.representedElementKind {
// Non nil: It is a supplementary View
if kind == UICollectionElementKindSectionHeader {
// HEADER
var frame = attributes.frame
frame.origin.y = frame.origin.y + frame.size.height
frame.size.width = sectionInset.left
attributes.frame = frame
}
}
else{
// Nil: It is an item
}
}
return copiedAttributes
}
另外,为了好的衡量(?),我采用了协议UICollectionViewDelegateFlowLayout并实现了这个方法(虽然不清楚什么是优先的.然后,故事板文件中有设置,但那些似乎被运行时对应物覆盖):
func collectionView(
collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
referenceSizeForHeaderInSection section: Int) -> CGSize {
let left = (collectionViewLayout as! UICollectionViewFlowLayout).sectionInset.left
return CGSizeMake(left, 1)
}
…并且我成功地将标题降低到其部分的第一行;但是,标头最初占用的空间保持打开状态:
…我唯一可以做到的方法是将标题视图高度设置为1,将“剪辑子视图”设置为false,以便显示标签(如果我将高度设置为0,则不绘制标签),但这绝对不是最优雅的解决方案(并且可能会在-say-iOS 9.2中破解)
也就是说,标题的实际高度链接到各部分之间的垂直空间:我不能将空间设置为零,同时将标题视图保持在合理的大小以便显示.
也许我也应该将所有部分项目向上移动(与我的标题高度相同),以填补空洞?
最佳答案
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSArray *originalAttributes = [super layoutAttributesForElementsInRect:rect];
NSMutableArray *allAttributes = [NSMutableArray new];
for (UICollectionViewLayoutAttributes* attributes in originalAttributes) {
[allAttributes addObject:[attributes copy]];
}
for (UICollectionViewLayoutAttributes *attributes in allAttributes) {
NSString *kind = attributes.representedElementKind;
if (kind == UICollectionElementKindSectionHeader) {
CGRect frame = attributes.frame;
UICollectionViewLayoutAttributes *cellAttrs = [super layoutAttributesForItemAtIndexPath:attributes.indexPath];
frame.origin.x = frame.origin.x;
frame.size.height = self.sectionInset.top;
frame.size.width = cellAttrs.frame.size.width;
attributes.frame = frame;
}
}
return allAttributes;
}