下面是我的自定义布局类的layoutAttributes方法。对于第0部分，layoutAttributes为零，因此，第一部分标题不会显示。
“layoutAttributedForElementsInRect：0”和“在这里输入”中的“打印”。
对于其余部分，- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSMutableArray *answer = [[super layoutAttributesForElementsInRect:rect] mutableCopy];
UICollectionView *const cv = self.collectionView;
CGPoint const contentOffset = cv.contentOffset;
NSMutableIndexSet *missingSections = [NSMutableIndexSet indexSet];
for (UICollectionViewLayoutAttributes *layoutAttributes in answer)
{
if (layoutAttributes.representedElementCategory == UICollectionElementCategoryCell)
{
[missingSections addIndex:layoutAttributes.indexPath.section];
}
}
for (UICollectionViewLayoutAttributes *layoutAttributes in answer)
{
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader])
{
[missingSections removeIndex:layoutAttributes.indexPath.section];
}
}
[missingSections enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:idx];
NSLog(@"Section in layoutAttributedForElementsInRect: %ld", indexPath.section);
UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
if (layoutAttributes != nil)
{
[answer addObject:layoutAttributes];
}
else
{
NSLog(@"Entered here");
}
}];
for (UICollectionViewLayoutAttributes *layoutAttributes in answer)
{
if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader])
{
NSInteger section = layoutAttributes.indexPath.section;
NSInteger numberOfItemsInSection = [cv numberOfItemsInSection:section];
NSIndexPath *firstCellIndexPath = [NSIndexPath indexPathForItem:0 inSection:section];
NSIndexPath *lastCellIndexPath = [NSIndexPath indexPathForItem:MAX(0, (numberOfItemsInSection - 1)) inSection:section];
NSIndexPath *firstObjectIndexPath = [NSIndexPath indexPathForItem:0 inSection:section];
NSIndexPath *lastObjectIndexPath = [NSIndexPath indexPathForItem:MAX(0, (numberOfItemsInSection - 1)) inSection:section];
UICollectionViewLayoutAttributes *firstObjectAttrs;
UICollectionViewLayoutAttributes *lastObjectAttrs;
if (numberOfItemsInSection > 0)
{
firstObjectAttrs = [self layoutAttributesForItemAtIndexPath:firstObjectIndexPath];
lastObjectAttrs = [self layoutAttributesForItemAtIndexPath:lastObjectIndexPath];
}
else
{
firstObjectAttrs = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader
atIndexPath:firstObjectIndexPath];
lastObjectAttrs = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter
atIndexPath:lastObjectIndexPath];
}
CGFloat headerHeight = CGRectGetHeight(layoutAttributes.frame);
CGPoint origin = layoutAttributes.frame.origin;
origin.y = MIN(
MAX(
contentOffset.y + cv.contentInset.top,
(CGRectGetMinY(firstObjectAttrs.frame) - headerHeight)
),
(CGRectGetMaxY(lastObjectAttrs.frame) - headerHeight)
);
layoutAttributes.zIndex = 1024;
layoutAttributes.frame = (CGRect) {
.origin = origin,
.size = layoutAttributes.frame.size
};
}
}
return answer;
}
不是零。
UICollectionViewDelegate 更新：collectionView:viewForSupplementaryElementOfKind:atIndexPath:方法。
第0节不执行- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
CGSize retval = CGSizeMake(50, 50);
retval.height += 35; retval.width += 35;
return retval;
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
return UIEdgeInsetsMake(10, 15, 10, 15);
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
NSLog(@"Section = %ld", indexPath.section);
UICollectionReusableView *reusableview = nil;
if (kind == UICollectionElementKindSectionHeader)
{
UICollectionReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
UILabel *headerLabel;
headerLabel = [[UILabel alloc]initWithFrame:CGRectMake(120, 10, 100, 30)]
headerLabel.backgroundColor = [UIColor lightGrayColor];
headerLabel.textColor = [UIColor blackColor];
headerLabel.text = @"hello";
[headerView addSubview:headerLabel];
reusableview = headerView;
}
return reusableview;
}
。“Section = 1”是第一个记录的语句。
{{1}}
答案 0 :(得分：1)
第一部分layoutAttributes为零的原因是
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath为此部分返回nil。当标题的大小为0时会发生这种情况。
所以，我认为你错过了委托方法：
collectionView:layout:referenceSizeForHeaderInSection。尝试实现它并确保它为所有部分返回非零值。
让我知道它是如何运作的。