CollectionView上的headerView滞留问题

最新推荐文章于 2024-04-06 09:45:08 发布

原创最新推荐文章于 2024-04-06 09:45:08 发布 · 1.2k 阅读

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本文详细介绍了如何在UICollectionView中实现类似于UITableView的HeaderView滞留功能。通过继承UICollectionViewFlowLayout类并覆盖特定方法，开发者可以控制HeaderView的行为，确保其在滚动过程中保持可见。此教程将指导您完成关键步骤，包括创建自定义布局类、覆盖方法以及调整HeaderView的位置。

CollectionView上的HeaderView默认是不会想tableView一样滞留的，若想滞留，则进行一下操作：

1. 创建类，继承 UICollectionViewFlowLayout

2. 在类中拷贝一下两个方法，即可

- (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];
        
        UICollectionViewLayoutAttributes *layoutAttributes = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
        
        [answer addObject:layoutAttributes];
        
    }];
    
    for (UICollectionViewLayoutAttributes *layoutAttributes in answer) {
        
        if ([layoutAttributes.representedElementKind isEqualToString:UICollectionElementKindSectionHeader]) {
            
            NSInteger section = layoutAttributes.indexPath.section;
            NSInteger numberOfItemsInSection = [cv numberOfItemsInSection: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;
    
}

- (BOOL) shouldInvalidateLayoutForBoundsChange:(CGRect)newBound {

    return YES;
    
}