您还必须注意浮动部分的平面样式与没有浮动部分的分组样式之间的区别.

我做了一个支持这个计算的类别：

@interface UITableView (VisibleSections)
 
// Returns an array of NSNumbers of the current visible section indexes
- (NSArray *)indexesOfVisibleSections;
// Returns an array of UITableViewHeaderFooterView objects of the current visible section headers
- (NSArray *)visibleSections;
 
@end
 
@implementation UITableView (VisibleSections)
 
- (NSArray *)indexesOfVisibleSections {
    // Note: We can't just use indexPathsForVisibleRows,since it won't return index paths for empty sections.
    NSMutableArray *visibleSectionIndexes = [NSMutableArray arrayWithCapacity:self.numberOfSections];
    for (int i = 0; i < self.numberOfSections; i++) {
        CGRect headerRect;
        // In plain style,the section headers are floating on the top,so the section header is visible if any part of the section's rect is still visible.
        // In grouped style,the section headers are not floating,so the section header is only visible if it's actualy rect is visible.
        if (self.style == UITableViewStylePlain) {
            headerRect = [self rectForSection:i];
        } else {
            headerRect = [self rectForHeaderInSection:i];
        }
        // The "visible part" of the tableView is based on the content offset and the tableView's size.
        CGRect visiblePartOfTableView = CGRectMake(self.contentOffset.x,self.contentOffset.y,self.bounds.size.width,self.bounds.size.height);
        if (CGRectIntersectsRect(visiblePartOfTableView,headerRect)) {
            [visibleSectionIndexes addObject:@(i)];
        }
    }
    return visibleSectionIndexes;
}
 
- (NSArray *)visibleSections {
    NSMutableArray *visibleSects = [NSMutableArray arrayWithCapacity:self.numberOfSections];
    for (NSNumber *sectionIndex in self.indexesOfVisibleSections) {
        UITableViewHeaderFooterView *sectionHeader = [self headerViewForSection:sectionIndex.intValue];
        [visibleSects addObject:sectionHeader];
    }
 
    return visibleSects;
}
 
@end